Hello- I have a 2000 Blazer with 123,000 miles. It currently has very low power. I cannot get any acceleration out of it. The exhaust sounds like the engine is running against itself. I have been struggling with this for a year now. I do most of my own work.
At first I thought the exhaust was plugged. Midas put on a new convertor and muffler. No change. The plugs, wires, cap and rotor are new.
I then broke down and took it to a dealer. They said the exhaust is plugged. I took it back to Midas. Put a 2nd convertor and muffler on.
No change.
Tried to go on vacation pulling a smal camper- Problem got worse. Had another GM dealer look at it - could not determine problem.
No check engine light.
Since then I have-
Installed new intake gaskets
New fuel filter
New fuel pump
New timing chain
Tried a used ignition module,coil,and fuel injection spider.
All of these did nothing. The fuel spider actually made it worse.
I have had it hooked up to a Snap On computer. All the sensors appear to be doing what they are supposed to.
The problem is in the timing. At idle it is 20 BTDC. Try to throttle up and it starts to advance but when the engine hits around 3000 rpm the timing retards to less than 10. The timing is not advancing like it should. The knock sensor and MAP sensors are both creating the proper voltage signal to the ECM. Shop floor no load RPM's rarely get over 3500. When they do the timing is not retarding as far. What else can affect timing?
This is my first posting. I have been able to try other ideas that I have seen posted here on this web sight.
Thank you for reading.

Check engine vacuum at idle and at 2K rpm and post back vacuum readings.
What were the camshaft retard readings on the scanner?
How is the fuel pressure?

If you ever find the cause, PLEASE make sure to post the fix. I also have a 2000 Blazer (125,000 miles) that suffers from relatively low power despite more-or-less everything being new AC Delco parts, good oil and fuel pressure and no codes whatsoever. I can live with mine, but I know the power is not nearly what it should be, and I wouldn't even try to tow with it. I have been monitoring the board for quite a while now, and it seems that there is some problem peculiar to 2000 Blazers that causes this problem -- although I've never seen a solution. Whenever I have seen a "low power" post with no other problems, more often than not it seems to involve a 2000. A somewhat odd sidenote -- a little while after I replaced my lower intake gasket, I ran a quart of block flushing solvent in the crankcase for the recommended number of minutes, drained it and put in fresh oil and filter. During the test drive, it rode like I had installed a supercharger on the vehicle -- the increase in power was beyond incredible -- it seemed even better than when I bought it new. After that, the power gradually decreased over a few hundred miles and went back to "normal" since then, which was over a year ago. I've always changed the oil and filter every 3000 miles from new, so I assumed it was not a general sludge problem. I don't know what any of this means (is there some offending senser that the block flush temporarily cleaned?), or whether it could be related to the problem you are having. But anyway, good luck finding your problem.

Did you have the problem before you installed new intake gaskets?

Yes.

Check engine vacuum at idle and at 2K rpm and post back vacuum readings.
What were the camshaft retard readings on the scanner?
How is the fuel pressure? Thank you for responding.

I do not have a vacuum gauge. The MAP readings on the scanner are
10.7" HG at idle
1.36 V at idle
8.9" HG at 2000 RPM
1.0 V at 2000 RPM
As long as the MAP sensor is good these readings should be accurate. Should this be confirmed with a gauge connected directly to the manifold?
Camshaft retard is at -11 degrees both at idle and 2000 rpm.
Fuel psi is 60 psi peaking at 65. I installed a new fuel pump and inline filter. The reading had been 55 psi. The new pump made no change at all in the power.
I work in parts at a medium duty GM dealer. Some of the techs at work thinks it is the injectors. They test good on the scanner. I realize this only checks them electronically. It would not detect a bad spray pattern or uneven fuel delivery. I tried a used fuel injector spider but who knows how long it had sit or how many miles were on it. I may try a new one this weekend. Has anyone changed them and how many miles did you have on the truck? Did you gain power?

Thank you for responding. The problem did exist before I changed the intake manifold gaskets. Even though I could not find an exhaust leak( by spraying carb cleaner around manifold) I was at wits end. The old gaskets looked good coming off. The new ones did not make it better.
I have been working this problem fo a long time. I am starting to suspect the injectors more and more. (see other reply) I have a friend with a 2000 Blazer with this same problem. A lot of people I talk to though say this 4.3 L is a good little powerful engine. Mine used to be.

>>Has anyone changed them and how many miles did you have on the truck? Did you gain power?<<

I replaced the OEM spider in my 2000 (currently 125,000 miles) with the recommended replacement GM unit about 10 months ago. My old unit's pressure regulator was leaking down causing hard starts. It solved the hard starting problem, but did nothing whatsoever to improve the low power problem. I am thinking about replacing the Oxygen sensors (mine have never been replaced) even though I am getting no codes and it passes emissions easily. Have you tried replacing your O2 sensors?

Thank you for responding.

I do not have a vacuum gauge. The MAP readings on the scanner are
10.7" HG at idle
1.36 V at idle
8.9" HG at 2000 RPM
1.0 V at 2000 RPM
As long as the MAP sensor is good these readings should be accurate. Should this be confirmed with a gauge connected directly to the manifold?
Camshaft retard is at -11 degrees both at idle and 2000 rpm.
Fuel psi is 60 psi peaking at 65. I installed a new fuel pump and inline filter. The reading had been 55 psi. The new pump made no change at all in the power.
I work in parts at a medium duty GM dealer. Some of the techs at work thinks it is the injectors. They test good on the scanner. I realize this only checks them electronically. It would not detect a bad spray pattern or uneven fuel delivery. I tried a used fuel injector spider but who knows how long it had sit or how many miles were on it. I may try a new one this weekend. Has anyone changed them and how many miles did you have on the truck? Did you gain power?

The vacuum gauge check test for restricted exhaust system.
You can pickup a vacuum gauge at parts place or tool dealer cheap.
One of the first and cheapest test tools made.

Yor camshaft retard reading/setting is bad.
You need to bring it in as close to 0 degress as you can.
Shoulds not be over -2 or + 2 degrees at the most.

If the no adjustable dist and off 11 degres you may have to remove dist and turn the dist gear a half turn to get it back in.
Rebuilt or exchange dist sometimes the gear not timed/set right.
A half turn will change it around 10 to 12 degrees.
http://files.automotiveforums.com/gallery/showphoto.php?photo=51302

Unless you are on top of a mountain 10 in hg maf sensor reading is not good.
What is you sea level altitude?
Do you have any fuel trim short or long term readings?

In. hg at 2000 ft should be around 28 in. hg and 29 at 1000 ft.

Yor camshaft retard reading/setting is bad.
You need to bring it in as close to 0 degress as you can.
Shoulds not be over -2 or + 2 degrees at the most.

If the no adjustable dist and off 11 degres you may have to remove dist and turn the dist gear a half turn to get it back in.
Rebuilt or exchange dist sometimes the gear not timed/set right.
A half turn will change it around 10 to 12 degrees.
http://files.automotiveforums.com/gallery/showphoto.php?photo=51302

This IS a big problem, you may have found your problem. My opinion, you need to get this figured out. Follow MT instructions, half turn and get it dialed in to the proper settings and go from there.

Hello- No, I have not tried to replace the O2 sensor. They have passed and are fluxuating like they should. With the reply concerning the cam retard it looks like I beeter look at the distributor again. (see other replies) Thanks for your response.

The distributor is fixed. I have taken it out but I was very careful to put it back in where it came out. I will investigate further though. The GM tech that worked on it earlier this summer told me about a reference point on the dist. There is a small 6 and 8 cast into the housing of the dist. On a 6 cyl with #1 at TDC the rotor should point at the 6- likewise on an 8 cyl.
Thanks for your reply.
According to the local airport we are at 597 feet above sea level.

I have removed the distributor but was aware of engine position and TDC. I will inspect the drive gear. Could it be wore out? I tried a used dist. out of an engine that had blown. Now that I've typed this it makes me wonder it the dist. was bad in this engine and he just drove it till it blew!

Thanks for the bulletin. That is very helpful. I am confident that the exhaust is not restricted.
The original dist. is in the truck now. I started having this problem before I removed it. I remove it to try a different cam position sensor.
Thanks for your reply- I've got some things to check out.

You should be reading about 29.5 -29.4

Give it a good cleaning with MAF sensor cleaner and reset PCM and see what it reads.
Good luck
MT

I bought a vacuum gauge today. Vacuum readings taken at the brake booster vacuum hose port is 19" at idle and 20" at 2000 RPM. The needle is very steady. Goes to 0 and then up to 25" before resting at 19" when the throttle is snapped. The scanner still reads 10.7 though. I did try to clean it. It did not improve any. Is this an indication that the MAP sensor is bad?
I have not checked the cam reference points yet.

I have trim readings as follows
ST Trim 1 121
ST Trim 1 % -5%
LT Trim 1 120
LT Trim 1 % -6%
ST Trim 2 120
ST Trim 2 % -6
LT Trim 2 120
LT Trim 2 % -6%
At the risk of show what my lack of knowledge is - What do these reading show?
I also question the MAP reading which is 10.7. There is another reading which is called BARO. This reading is 29" Hg. What is BARO?
Thank you.

Baro is the allitude from seal level.
29.0 is 1000 ft above seal level
The Baro reading comes from Mass air flow sensor.
MAP is engine vacuum.
It comes from map sensor.
It should read the engne vacuum.
18-20 HG no load on engine.
Full load or thottle snap it will drop way down.
If only reading 10 and actual engine vacuum is 18-20 range.
Check vacuum to it and if ok check or replace MAP sensor.
MT

I installed new MAP sensor no change. I put gauge in same hole as sensor and read 19 Hg. I think I read the scanner tool wrong. The difference between the MAP readout and the MAF read out is 19. That is my vacuum.

I installed a new distributor. No change in power but the cam retard is now 0 degrees. I found 2 timing hash marks on the balancer. At first I thought the timing was off one tooth. When I lined up the first mark the old dist. was off. I installed the new one dead on the referece point. Truck would not start!! Went back to other point and truck started. Cam retard is 0 but perfrmance is still poor.
When a go into hard accel from stop the RPM maxs out at around 3000, vehicle speed is 40-45 with the engine misfiring, pinging and knocking. ADV is around 10-12. Knock sensor reading is fluctuating like it is trying to advance timing. If I accelerate gradually I eventually get to 55, the engine is quiet but is laboring. Timing is between 10-15 degrees.
Help!!!

Have you tried changing the mass air flow sensor? I've been doing a lot of reading and that may be my next step. The scanner I use indicates it is reading air but it may be sending a misleading signal to the ECM. Let me know if you have.
Thanks.

After you try all that, I installed a OFF ROAD MSD with a MSD coil and MSD plug wires. This made a very larger noticable difference.
I also use Royal Purple oil with a K&N oil filter. Believe it or not this oil works just as it claims. I have tried every highend oil and it is the only one where you can feel how smooth is runs and see yourself spending less on gas.

I also use a Helix throttle body spacer with a K&N air filter.
Have fun.
Vern

Have you tried changing the mass air flow sensor? I've been doing a lot of reading and that may be my next step. The scanner I use indicates it is reading air but it may be sending a misleading signal to the ECM. Let me know if you have.
Thanks.

No, mine is original, and has never thrown a code.

No, mine is original, and has never thrown a code.

Mine has not thrown a code either. I found the same symptoms on another website forum. I think he said his didn't code either. It had around 120,000 miles on it. I did try to clean it. No change. I'll keep this thread posted as to what I do next.

Baro is the allitude from seal level.
29.0 is 1000 ft above seal level
The Baro reading comes from Mass air flow sensor.
MAP is engine vacuum.
It comes from map sensor.
It should read the engne vacuum.
18-20 HG no load on engine.
Full load or thottle snap it will drop way down.
If only reading 10 and actual engine vacuum is 18-20 range.
Check vacuum to it and if ok check or replace MAP sensor.
MT

I think my next step is a MAF sensor. I read another forum with the same performance symptoms as mine. It checks out OK and doesn't throw a code. It reads 6.5 MHz at idle. My info says spec is 5-7. Will a MAF sensor cause the timing to retard? I also notice that during hard acceration it will only get up to about 35 MPH, one of the O2 sensors reads lean while the other reads rich. This does not change till I let off the accelerator and slowly get up to 55. When I do the O2 sensor fluxuate like they should.

I think my next step is a MAF sensor. I read another forum with the same performance symptoms as mine. It checks out OK and doesn't throw a code. It reads 6.5 MHz at idle. My info says spec is 5-7. Will a MAF sensor cause the timing to retard? I also notice that during hard acceration it will only get up to about 35 MPH, one of the O2 sensors reads lean while the other reads rich. This does not change till I let off the accelerator and slowly get up to 55. When I do the O2 sensor fluxuate like they should.


MAF does not change timing.

It controls fuel mix.

If fuel mix is off the scanner will read heavy + or - on long terms fuel trims.
What is long and short term fuel mix?

MAF does not change timing.

It controls fuel mix.

If fuel mix is off the scanner will read heavy + or - on long terms fuel trims.
What is long and short term fuel mix? Thank you for responding

Readings are as follows
ST trim 1 fluxuates between 126-129. The % fluxuates between 0 and -2%
LT Trim 1 reads a steady 112 with the % at -12 and holding
ST trim 2 fluxuates between 127-129 with the % between -1 - +2%
LT Trim 2 reads a steady 113 with the % at 12% and holding.

My check engine light came on yesterday. I checked the codes this morning
I have
p0300 Misfire
p0101 Mass air out of range
p0143
p0131

I accidently cleared the codes before reading what the last 2 meant.
Does the P0101 indicate I have a bad MAF sensor?
Thank you




Thanks for your help.

MAF does not change timing.

It controls fuel mix.

If fuel mix is off the scanner will read heavy + or - on long terms fuel trims.
What is long and short term fuel mix?

I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings

Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%

I was tryng to accelerate. Engine was runninig very rough with very little power. Do any of these readings help in telling what is wrong. I have not tried a MAF sensor yet. Since it has a code now I'm thinking that this may be the problem. It still does not explain why the timing changes.

I too have the same sluggish acceleration problem along with low MPG. At least in my opinion it is low MPG. This is a new vehicle to me so I only have one average MPG reading based on a half tank of gas - 14.5 MPG. However, to be fair this is based on city driving, in sweltering heat 90 to 100 degrees, with the auto temp set at 78. Is 14.5 MPG normal under those conditions? We just put $1800 into general maintenance repairs that included new spark plugs and wires, fuel filter and alignment with tire rotation and balance. We also made some other maintenance repairs, but they would not have any affect on sluggish acceleration or MPG. I have read the other posts but I have no computer readings to compare the performance. There are no codes showing or trouble lights on that would indicate that there is a problem. Is this poor performance or normal for the 2000 Bravada?

I too have the same sluggish acceleration problem along with low MPG. At least in my opinion it is low MPG. This is a new vehicle to me so I only have one average MPG reading based on a half tank of gas - 14.5 MPG. However, to be fair this is based on city driving, in sweltering heat 90 to 100 degrees, with the auto temp set at 78. Is 14.5 MPG normal under those conditions? We just put $1800 into general maintenance repairs that included new spark plugs and wires, fuel filter and alignment with tire rotation and balance. We also made some other maintenance repairs, but they would not have any affect on sluggish acceleration or MPG. I have read the other posts but I have no computer readings to compare the performance. There are no codes showing or trouble lights on that would indicate that there is a problem. Is this poor performance or normal for the 2000 Bravada?


Welcome to AF
If you have a problem on yours it is best to start a new thread and some one will help.
Two different problems on on post gets confusing.:grinyes:

http://www.automotiveforums.com/vbulletin/showthread.php?p=4820845#post4820845

http://www.automotiveforums.com/vbulletin/newthread.php?do=newthread&f=2072

But I would check it on a long highway drive to get a good idea of the actual fuel mileage.
And go by how many gallons it takes to fill it back up after starting with a full tank.
Just gauge reading is not a very good way to judge mileage.
MT

I too have the same sluggish acceleration problem along with low MPG. At least in my opinion it is low MPG. This is a new vehicle to me so I only have one average MPG reading based on a half tank of gas - 14.5 MPG. However, to be fair this is based on city driving, in sweltering heat 90 to 100 degrees, with the auto temp set at 78. Is 14.5 MPG normal under those conditions? We just put $1800 into general maintenance repairs that included new spark plugs and wires, fuel filter and alignment with tire rotation and balance. We also made some other maintenance repairs, but they would not have any affect on sluggish acceleration or MPG. I have read the other posts but I have no computer readings to compare the performance. There are no codes showing or trouble lights on that would indicate that there is a problem. Is this poor performance or normal for the 2000 Bravada?

I'm new here too. The problem I am having is bad enough that the vehicle is nearly unsafe to drive. When I put the pedal to the floor it will not speed up. I have to very gradually accelerate. I drive like the is an egg on the pedal.
Now I know I shouldn't floor it every time I go somewhere. The engine is not creating any power though. The best mileage I got was on a long interstate run. It can get up to around 20-22 depending on how fast and how loaded. That was when everything was working good. Keep reading you may see some other ideas.

K&N air filters are a known problem when used on vehicles with MAF sensors. The MAF sensor uses two "wires" and a heated wire for sensing purposes. The oil from the air filter coats the "wires" in the MAF sensor causing incorrect readings. Carefully clean the sensor "wires" with a spray type brake cleaning solvent. Brake cleaner leaves no residue, carb cleaner does.

Have you checked fuel pressure and leakdown?

K&N air filters are a known problem when used on vehicles with MAF sensors. The MAF sensor uses two "wires" and a heated wire for sensing purposes. The oil from the air filter coats the "wires" in the MAF sensor causing incorrect readings. Carefully clean the sensor "wires" with a spray type brake cleaning solvent. Brake cleaner leaves no residue, carb cleaner does.

Have you checked fuel pressure and leakdown?

Yes fuel pressure is good, it runs 60-65 psi. I do not have a K&N filter. I have replace the fuel pressure module, fuel pump, and filter. I have also tried cleaning the MAF wires. All of this has not improved my problem. As stated earlier the timing seems to be the main issue. At idle it is 20 degrees BTDC. At 3000 rmp it is 10 degrees.

Sorry to hear you haven't found your problem yet. My thoughts keep going back to what I mentioned about my 2000 Blazer in my response to your original post:

"I ran a quart of block flushing solvent in the crankcase for the recommended number of minutes, drained it and put in fresh oil and filter. During the test drive, it rode like I had installed a supercharger on the vehicle -- the increase in power was beyond incredible -- it seemed even better than when I bought it new. After that, the power gradually decreased over a few hundred miles and went back to "normal" since then, which was over a year ago. I've always changed the oil and filter every 3000 miles from new, so I assumed it was not a general sludge problem. I don't know what any of this means (is there some offending senser that the block flush temporarily cleaned?), or whether it could be related to the problem you are having."

If you are willing to take the risk (as I did) of using block flush in a high mileage engine (I did it because some coolant had leaked into my crankcase from the bad lower intake gasket), it would be interesting to see if you experience the same dramatic, albeit temporary, power boost that I experienced. Of course, if it does drastically improve your power as it did mine, it still doesn't exactly explain the cause of the problem. As a side note, I have never used a K&N air filter either -- my Blazer has been 100% stock from new and has always been properly maintained on or ahead of schedule. I don't remember the particular brand of flush I used, but I bought it at Autozone and it was in an old-fashioned 1 quart metal oil can -- the kind they sold oil in before they came out with plastic bottles with screw-off caps. Good luck.

Yes fuel pressure is good, it runs 60-65 psi. I do not have a K&N filter. I have replace the fuel pressure module, fuel pump, and filter. I have also tried cleaning the MAF wires. All of this has not improved my problem. As stated earlier the timing seems to be the main issue. At idle it is 20 degrees BTDC. At 3000 rmp it is 10 degrees.

Timing is not adjustable.
The VCM controls timing.
Did you ever get the camshaft retard setting set right.
What is it reading?

Timing is not adjustable.
The VCM controls timing.
Did you ever get the camshaft retard setting set right.
What is it reading?
Yes, I replaced the distributor with a new cam position sensor. The cam retard reading is now 0 degrees. There where 2 marks on the harmonic balancer. I have marked the one with paint, that gives me the reading of 0 cam retard. The fuel trim readings are in previous replies if you still need that info. thank you.

Sorry to hear you haven't found your problem yet. My thoughts keep going back to what I mentioned about my 2000 Blazer in my response to your original post:

"I ran a quart of block flushing solvent in the crankcase for the recommended number of minutes, drained it and put in fresh oil and filter. During the test drive, it rode like I had installed a supercharger on the vehicle -- the increase in power was beyond incredible -- it seemed even better than when I bought it new. After that, the power gradually decreased over a few hundred miles and went back to "normal" since then, which was over a year ago. I've always changed the oil and filter every 3000 miles from new, so I assumed it was not a general sludge problem. I don't know what any of this means (is there some offending senser that the block flush temporarily cleaned?), or whether it could be related to the problem you are having."

If you are willing to take the risk (as I did) of using block flush in a high mileage engine (I did it because some coolant had leaked into my crankcase from the bad lower intake gasket), it would be interesting to see if you experience the same dramatic, albeit temporary, power boost that I experienced. Of course, if it does drastically improve your power as it did mine, it still doesn't exactly explain the cause of the problem. As a side note, I have never used a K&N air filter either -- my Blazer has been 100% stock from new and has always been properly maintained on or ahead of schedule. I don't remember the particular brand of flush I used, but I bought it at Autozone and it was in an old-fashioned 1 quart metal oil can -- the kind they sold oil in before they came out with plastic bottles with screw-off caps. Good luck.

I have seen oil flush before. I'm not due for an oil change for awhile but I may try it. I have nothing to loose. Thanks and keep reading this thread.

Yes, I replaced the distributor with a new cam position sensor. The cam retard reading is now 0 degrees. There where 2 marks on the harmonic balancer. I have marked the one with paint, that gives me the reading of 0 cam retard. The fuel trim readings are in previous replies if you still need that info. thank you.

The cam retard has to be set with a good engine capable scanner.
The timing marks on crank has nothing to do with camshaft retard.
Camshaft retard is the position the rotor fires the plugs wires.
Say no to a engine flush pitch it in the trash can.
Many engine have been killed with engine flush crap.:grinyes:
MT

The cam retard has to be set with a good engine capable scanner.
The timing marks on crank has nothing to do with camshaft retard.
Camshaft retard is the position the rotor fires the plugs wires.
Say no to a engine flush pitch it in the trash can.
Many engine have been killed with engine flush crap.:grinyes:
MT

I was useing the marks on the balancer to determine where TDC was and check the reference point of the distributor. You had indicated in an earlier post were the rotor should be pointing. I had lined up the mark on the balance with the notch in the timing cover. At first the rotor was not correct. When I moved it to correct it- the engine would not start. Thats when I found two marks. I went ahead and installed a rebuilt distributor. The screw holes for the cap holddown were stripped out. I lined it up with the mark that I thought was correct. The engine started right up and the cam retard readout was 0. I do not know how cam shaft retard is set with the scanner. If it is currently reading 0 it should be OK. Right?
thank you.

The actual engine timing is set and controlled by the crankshaft senor and VCM.
The engine timing is not adjustable.

Setting the dist or camshaft retard is the pointing the rotor to fire direct on the plug wire terminal.

Camshaft retard is not checked or set with a timing light or timing marks.
You need a good engine capable scanner that will read out the camshaft retard.
It will read out it in - or + degrees and only updates the reading with engine running over 1K rpm.
Turn the dist so the camshaft retard setting in the scanner reads as close to zero degrees as you can get it or 1-2 degrees - or +.

If the setting is over 3 degrees off it can give some engine running problems and even misfire.
If rotor is not centered on plug wire it will also increase spark and burn plugs and wire from hot spark and long term piston melt down.



Some are a pain to set as some dist are not adjustable and some rebuilt dist gears are put on a half turn off.

The cam retard has to be set with a good engine capable scanner.
The timing marks on crank has nothing to do with camshaft retard.
Camshaft retard is the position the rotor fires the plugs wires.
Say no to a engine flush pitch it in the trash can.
Many engine have been killed with engine flush crap.:grinyes:
MT

I'm a little confused. I used the marks on the balancer as a reference to install the new distributor. The cam retard now reads 0 degrees on the scanner. Does it still need to be set? I was borrowing a Snap-On scanner. I am unsure of the model but it would do everything you needed it to. Are the fuel trim readings I posted out of spec?
Thank you.

I'm a little confused. I used the marks on the balancer as a reference to install the new distributor. The cam retard now reads 0 degrees on the scanner. Does it still need to be set? I was borrowing a Snap-On scanner. I am unsure of the model but it would do everything you needed it to. Are the fuel trim readings I posted out of spec?
Thank you.

If it reads 0 degrees on a scanner you are set to go. Right on the money.

Clear codes and drive and recheck the fuel trims and for any codes coming back.
The lower the fuel trims the better.
Post back after re driving.
MT

If it reads 0 degrees on a scanner you are set to go. Right on the money.

Clear codes and drive and recheck the fuel trims and for any codes coming back.
The lower the fuel trims the better.
Post back after re driving.
MT

I have cleared the codes.
What would lower trim codes read. I do not know what would be considered high. Are these readings high?

Readings are as follows
ST trim 1 fluxuates between 126-129. The % fluxuates between 0 and -2%
LT Trim 1 reads a steady 112 with the % at -12 and holding
ST trim 2 fluxuates between 127-129 with the % between -1 - +2%
LT Trim 2 reads a steady 113 with the % at 12% and holding.

Truck still has no power and the timing is still retarding to around 10 degrees at 3000 RPM.

In a previous post , after I installed the new distributor, I recorded a MAF sensor code. If these fuel trim readings are out of spec, should I change the MAF sensor? I have already tried cleaning it. I may try 1 more time though.

Thank you for your input.

I have cleared the codes.
What would lower trim codes read. I do not know what would be considered high. Are these readings high?

Readings are as follows
ST trim 1 fluxuates between 126-129. The % fluxuates between 0 and -2%
LT Trim 1 reads a steady 112 with the % at -12 and holding
ST trim 2 fluxuates between 127-129 with the % between -1 - +2%
LT Trim 2 reads a steady 113 with the % at 12% and holding.

Truck still has no power and the timing is still retarding to around 10 degrees at 3000 RPM.

In a previous post , after I installed the new distributor, I recorded a MAF sensor code. If these fuel trim readings are out of spec, should I change the MAF sensor? I have already tried cleaning it. I may try 1 more time though.

Thank you for your input.

Fuel trims is way off.
If one side is way + and other side is way -.
One side is rich and one side is way lean.
MT

I been here before!
My problem was the MAF.
id floor the truck ,and it felt like i was pulling a house not on wheels.
to check it: unplug the MAF and drive,if the MAF is bad you will feel the HUGE power gain,if the MAF isnt bad you wont feel any difference.
Unplug it and go for a ride.:smokin:
CS

Please forgive my ignorance, but what is the MAF, where is it, and how do I unhook it?

MASS AIR FLOW METER or SENSOR.
Its called both....
Its located just behind the air box on the air intake hose 1 clip 3 wires.
There should be 2 sets of wires 1 has 2 wires the other has 3.
CS

Thanks so much, it did seem to increase the power. Since disconnecting the MAF my check engine soon light has come on. I have reconnected the MAF, but can't get the light to go off. How do I reset it?

Thanks so much, it did seem to increase the power. Since disconnecting the MAF my check engine soon light has come on. I have reconnected the MAF, but can't get the light to go off. How do I reset it?

you can pull the + battery cable for a few minutes,that will reset the computer.
I ran with my light on for ages.
Glad it helped

I been here before!
My problem was the MAF.
id floor the truck ,and it felt like i was pulling a house not on wheels.
to check it: unplug the MAF and drive,if the MAF is bad you will feel the HUGE power gain,if the MAF isnt bad you wont feel any difference.
Unplug it and go for a ride.:smokin:
CS

I have tried unplugging the MAF sensor. I gain RPMs and that is it. I do not get any more HP. On the shop floor no load with sensor plugged in, I get about 3500 rpm. Unplugged it will redline. Take it out on the road it still struggles to get up to and maintain 55 MPH. The only difference I see is that the tranny shifts harder. The engine is not creating any torque.

If you read previous post, the timing retards back to around 10 degrees at 3000 RPM. It should be advancing. I'm beginning to think I have two items causing this problem.

Keep reading and I will post more results as I get them.

Thanks so much, it did seem to increase the power. Since disconnecting the MAF my check engine soon light has come on. I have reconnected the MAF, but can't get the light to go off. How do I reset it?

I have read other post where owners have cleaned the MAF sensor. You have to remove the component and use a cleaning solvent that you can buy at a parts store. Tell them what you are trying to clean so that you will get the right stuff. There are 3 wires inside the air tube of the MAF sensor. They are very fragile- but you should be able to spray the wires and improve your performance, if they are dirty. After 100,000 miles they may have a film on them. They are VERY sensitive to dirt.
Good luck.

Fuel trims is way off.
If one side is way + and other side is way -.
One side is rich and one side is way lean.
MT

Ok- It would appear then I also have a fuel problem along with a timining problem. Does the MAF sensor affect fuel trim? If not what does? Could it be the VCM throwing in the wrong amount of fuel of have I got bad injectors? If the fuel mixture is off, could it affect another sensor, which would tell the VCM to retard the timing? From reading the other post would you agree that changing out the MAF sensor might be a good place to start? I have tried cleaning it and it does not help. If I unplug it, I gain in RPM on the shop floor with no load. On the test drive though it still has very poor performance and low power. The transmission seems to shift harder also. It would appear to me I may have to replace either a MAF sensor, the injectors, a VCM or possibly a crank position sensor. Do you think I might be on the right track?

Thank you.

Ok- It would appear then I also have a fuel problem along with a timining problem. Does the MAF sensor affect fuel trim? If not what does? Could it be the VCM throwing in the wrong amount of fuel of have I got bad injectors? If the fuel mixture is off, could it affect another sensor, which would tell the VCM to retard the timing? From reading the other post would you agree that changing out the MAF sensor might be a good place to start? I have tried cleaning it and it does not help. If I unplug it, I gain in RPM on the shop floor with no load. On the test drive though it still has very poor performance and low power. The transmission seems to shift harder also. It would appear to me I may have to replace either a MAF sensor, the injectors, a VCM or possibly a crank position sensor. Do you think I might be on the right track?

Thank you.


Uneven fuel trim leads to problems with one side rich or lean.
Maf sensor should make both side high or low.
Run a cylinder balance or injector balance test.

I have had it hooked up to a Snap On computer. All the sensors appear to be doing what they are supposed to.
The problem is in the timing. At idle it is 20 BTDC. Try to throttle up and it starts to advance but when the engine hits around 3000 rpm the timing retards to less than 10. The timing is not advancing like it should. The knock sensor and MAP sensors are both creating the proper voltage signal to the ECM. Shop floor no load RPM's rarely get over 3500. When they do the timing is not retarding as far. What else can affect timing?
This is my first posting. I have been able to try other ideas that I have seen posted here on this web sight.
Thank you for reading.

I’ve read your problem and replies to your problem and I’m going to try to put in my 2 cents from my drag racing days.

When you say that your cam was retarded 10 degrees and now it’s close to zero in your other replies are you talking about your actual crank to camshaft timing, or are you talking about your ignition timing? I have to ask that because I’m not aware of any way to change the crank to camshaft timing without pulling the timing chain and either getting an offset crank key or triple-keyed crank sprocket.
Assuming that you are referring to ignition timing, if you are only getting 10 degrees total timing above 3000 RPM I don’t see how your motor could pull above 3500 RPM. I can take my drag race motor which can normally see 7000 to 8000 rpm and set the total timing to 10 degrees and it will not wing past 3500 RPM either. (Normally most naturally aspirated motors like somewhere in the neighborhood of 38 degrees of total timing from 3000 rpm and up, retarding a few degrees as you start getting above 6000 rpm or so)
I hooked my scanner up to my ’98 Chevy Blazer (which has pretty decent acceleration and mileage) and took it down the highway to see what kind of timing it was getting and it would go all the way up to 41 degrees total timing on the long flat stretches of highway backing down to 20 or so timing when it starts going up a grade.
If there’s no factory way to fix the timing you may need to look into an aftermarket performance programmer similar to the Jet – 15015 programmers available through places like Summit Racing as well as your local auto parts store, you can set different timing curves among other things with that.
Again I’m not saying that this is your only problem, but I could probably make most motors run with similar characteristics to yours (computer controlled or not) by simply backing the total timing down to 10 degrees, so if it was my motor that’s the first thing I would be worried about.

I’ve read your problem and replies to your problem and I’m going to try to put in my 2 cents from my drag racing days.

When you say that your cam was retarded 10 degrees and now it’s close to zero in your other replies are you talking about your actual crank to camshaft timing, or are you talking about your ignition timing? I have to ask that because I’m not aware of any way to change the crank to camshaft timing without pulling the timing chain and either getting an offset crank key or triple-keyed crank sprocket.
Assuming that you are referring to ignition timing, if you are only getting 10 degrees total timing above 3000 RPM I don’t see how your motor could pull above 3500 RPM. I can take my drag race motor which can normally see 7000 to 8000 rpm and set the total timing to 10 degrees and it will not wing past 3500 RPM either. (Normally most naturally aspirated motors like somewhere in the neighborhood of 38 degrees of total timing from 3000 rpm and up, retarding a few degrees as you start getting above 6000 rpm or so)
I hooked my scanner up to my ’98 Chevy Blazer (which has pretty decent acceleration and mileage) and took it down the highway to see what kind of timing it was getting and it would go all the way up to 41 degrees total timing on the long flat stretches of highway backing down to 20 or so timing when it starts going up a grade.
If there’s no factory way to fix the timing you may need to look into an aftermarket performance programmer similar to the Jet – 15015 programmers available through places like Summit Racing as well as your local auto parts store, you can set different timing curves among other things with that.
Again I’m not saying that this is your only problem, but I could probably make most motors run with similar characteristics to yours (computer controlled or not) by simply backing the total timing down to 10 degrees, so if it was my motor that’s the first thing I would be worried about.

Thanks for your response.
I do not fully understand cam retard. It has to do with the cam postion sensor in the distributor. It "reads" how musch wear is on the chain, telling the ECM where the cam is. Then the ECM can adjust ignition timining if needed. The performance of where my cam retard used to be VS being a 0 now is no difference.

The ignition timing is where I have the problem. I have to find out why my timing goes to 10 degrees at 3500. It is not creating power at all. Everything I have left to try is too expensive to just "try it and see". I think it will be one of the following, ECM, injectors, or a MAF sensor.

MT-2500 suggested a injector balance test. I hope to be able to do that soon. I borrowed the scanner I had and took it back.

Keep reading I hope to solve this soon.

The ignition timing is where I have the problem. I have to find out why my timing goes to 10 degrees at 3500. It is not creating power at all. Everything I have left to try is too expensive to just "try it and see". I think it will be one of the following, ECM, injectors, or a MAF sensor.

MT-2500 suggested a injector balance test. I hope to be able to do that soon. I borrowed the scanner I had and took it back.

Keep reading I hope to solve this soon.

The Injector balance test is a good idea also, if you've got a dead or weak cylinder that could also be the problem.
I noticed that AJT1961 in his reply noted that his 2000 Blazer was also low on power and he noticed a few other posts from other people with 2000 Blazers with the same "low power" problem and that's what got me to wondering if for some reason GM has a glitch in the 2000 programs for the Blazers that doesn't control the timing like it should.
It would be interesting if maybe another thread could be started and see if the other people with the low power 2000's (or any other years) could moniter their timing curves and post what they're seeing on the scanners as they drive down the highway or around town.

the cam timing is fine the -number comes from dist gear wear. the cam position sensor is in the dist so it tells the comp that the cam and crank is out of time when the dist gear is at fault. With it being out by just 11 a new gear should bring it close to 0 gm allows -2to +3 if it is to far out it can cause arcing in the cap because the coil will fire before it reaches the post in the dist cap. which can cause cross fire and this making the engine miss the comp only reads the timing when the rpms are raised above 2400rpm I think its 2400

Check the ignition control module.

the cam timing is fine the -number comes from dist gear wear. the cam position sensor is in the dist so it tells the comp that the cam and crank is out of time when the dist gear is at fault. With it being out by just 11 a new gear should bring it close to 0 gm allows -2to +3 if it is to far out it can cause arcing in the cap because the coil will fire before it reaches the post in the dist cap. which can cause cross fire and this making the engine miss the comp only reads the timing when the rpms are raised above 2400rpm I think its 2400

Thank you for the explanation.

Check the ignition control module.

I tried a different one and the old one was tested when it was in the shop. No difference.

Hey there everyone-
I was unable to do an injector balance test. From some of the techs I talked to and the miles on the vehicle I went ahead and replaced the injector "spider " assy. i came away with a very slight improvement.
I hooked it up to a scanner and the timing still retards. I work at a medium duty GMC dealer. I was able to look up on the computer, per VIN, a module located inside the VCM. It is called a Knock sensor module, p/n 16208961. If this is bad- would it cause the timing to retard?
Let me know if you have ever seen this problem.
Thanks

Hey there everyone-
I was unable to do an injector balance test. From some of the techs I talked to and the miles on the vehicle I went ahead and replaced the injector "spider " assy. i came away with a very slight improvement.
I hooked it up to a scanner and the timing still retards. I work at a medium duty GMC dealer. I was able to look up on the computer, per VIN, a module located inside the VCM. It is called a Knock sensor module, p/n 16208961. If this is bad- would it cause the timing to retard?
Let me know if you have ever seen this problem.
Thanks

That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.

The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.

But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.

Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT

That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.

The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.

But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.

Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT

I will have to check on tsb's. I finally found a knock sensor located at the back of the engine. The parts breakdown lists 2 but illustrates 1. The one I found is next to the oil pressure sensor just to the left of the distributor. The fuel supply and return pass right over it. Its is going to be difficult to even unplug. I can see it and even touch it but I cant disconnect it. Do you know where the second one is at?

The only reason I havnt looked at it before is when I checked it with the scanner the voltage fluctuated indicating it was working. If it runs great with it unplugged, do I need a new sensor or module? Other than a new computer that's the only thing that retards the timing, I think. I'll checkthe crank sensor sometime also. I'm taking it easy this weekend though. I'll check it next week. Have a good Labor Day Weekend!!

The check engine light came on over the weekend. I have a code P0420 for a catalyst efficiency low on bank 1.
I also have a code P0304 misfire on number 4.
The code P0420 is what has me concerned. What would cause a this code?

The check engine light came on over the weekend. I have a code P0420 for a catalyst efficiency low on bank 1.
I also have a code P0304 misfire on number 4.
The code P0420 is what has me concerned. What would cause a this code?

420 and 430 codes can be caused by engine running problems.
Fix missfire and engine running problems first.
Then clear codes and see if 420 or any other codes come back.
MT

That thing is giving you a fit.:grinyes:
The knock sensor module picks up the knock sensor signal and can and should retard the timing if a knock is present.
You might try and unplug the knock sensor and see what it does.
Check actual engine timing with a timing light and see if it matches the VCM/pcm readings.

The VCM gets it timing reference from the crankskaft sensor.
You might want to check it real close to.
If you have a lab scope it works goos on checking sensors.

But also remember the camshaft retard setting has nothing to do with the actual engine timing.
It only centers the dist rotor to fire direct on the plug wire terminal.


Is there any VCM reflashes out for your truck or tsb on it?
Good luck.
MT

It was so much work just to get to the knock sensor to even try to unplug it,I went ahead and replaced the knock sensor. it did not make any difference. I have checked for TSB's. I found one that has something to do with a transmission pressure switch. It bassically states that if the pressure is out of spec - to call the tech hotline. I just don't see how it has anything to do the tranny. Setting in neutral or park it still runs poorly.

I've been told that if the cranksensor was bad, it would have a hard start or no start condition. It starts good.
Thanks.

i would start looking at the computer if you can find a another blazer or jimmy with the same year and drive train you could try the comp out of that if you can find and owner one willing to help you

also your readings from the scanner with the throtel at 59% eng load should be higher than 25% i think the comp uses the maf senser to no the eng load
MAF gm/sec 43.68 seems high for only 25% load

I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings

Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%

also your readings from the scanner with the throtel at 59% eng load should be higher than 25% i think the comp uses the maf senser to no the eng load
MAF gm/sec 43.68 seems high for only 25% load

I threw a code today coming home. P0101 Mass Air circuit out of range.
I did a freeze frame on the scanner and received the following readings

Eng. load 25%
Coolant 149
ST Trim 185
ST trim % 44.5
LT Trim 138
LT Trim % 7.8
ST Trim 2 % -24.2
LT Trim 2 % 0
MAP 29.3
RPM 2306
Veh spd 52 mph
MAF gm/sec 43.68
TPS 59%

Do you know if the Eng. load affects the ignition timing? I have changed the MAP sensor and the knock sensor. The only other thing that I know of that controls the timing is the computer.

It was so much work just to get to the knock sensor to even try to unplug it,I went ahead and replaced the knock sensor. it did not make any difference. I have checked for TSB's. I found one that has something to do with a transmission pressure switch. It bassically states that if the pressure is out of spec - to call the tech hotline. I just don't see how it has anything to do the tranny. Setting in neutral or park it still runs poorly.

I've been told that if the cranksensor was bad, it would have a hard start or no start condition. It starts good.
Thanks.

I've changed the knock sensor- no change. Wht about the knock module in the VCM? If it has failed - will it retard it too much? If I remove it will the engine run? If it does and runs good- that might be my problem. Can the VCM be checked out somehow? I don't know of anything else that is making the timing retard so much.
Thanks

with a scanner with live data drive and see what your knock retard is and what your ignition advance is. it should advance as far as 45 degrees at times at least thats what mine does and it runs real strong. also watch what it does when you first hit the gas you really should not see any retard i have a live data scan gauge and the only time i see it retard in the timing is when towing and pulling a hill and it starts to ping on gas post back wat you record. also have you checked your tps

with a scanner with live data drive and see what your knock retard is and what your ignition advance is. it should advance as far as 45 degrees at times at least thats what mine does and it runs real strong. also watch what it does when you first hit the gas you really should not see any retard i have a live data scan gauge and the only time i see it retard in the timing is when towing and pulling a hill and it starts to ping on gas post back wat you record. also have you checked your tps

The scanner I had, I was borrowing. I have since returned it. I have never seen it advance more than 25 degrees. The timing retards to around 10 degrees with the TPS at 100%, RPM around 3000-3500. The engine is trying to get more RPM but it is missing and running rough because of the timing. I tried a new knock module(located inside the VCM), MAF sensor and an air temp sensor in the air intake. NO CHANGE!!!:banghead: I talked with a GM tech who really thought it was the MAF. He thought it was leaning out the mixture too much, this would cause a ping, so it retards the timing. All this leads to low power.
I've had it to two dealers. One was wrong. The other looked at it for 3 or 4 hours. When he told me whatever it is it wont be fixed today I told him to stop what youre doing. I cant afford that kind of comment. I work at a heavy duty truck dealer so I know about diesels and am mechanically inclined. I can do research and install parts myself. This has got me though:banghead:.

with a scanner with live data drive and see what your knock retard is and what your ignition advance is. it should advance as far as 45 degrees at times at least thats what mine does and it runs real strong. also watch what it does when you first hit the gas you really should not see any retard i have a live data scan gauge and the only time i see it retard in the timing is when towing and pulling a hill and it starts to ping on gas post back wat you record. also have you checked your tps

While I had the scanner the TPS reading did change smoothly as I moved the pedal. Don't think I havn't thought about changing it though. This thing has got a ghost I cannot figure out.

When it's fixed I'll post what was wrong.

Thanks for reply

I must have missed something... What year is the truck? That will make a difference, since the ECM/PCM would be different, and the control scheme would be different.

I must have missed something... What year is the truck? That will make a difference, since the ECM/PCM would be different, and the control scheme would be different.

It is a 2000. This thread has been going all summer. I hope that the first entries are still up for others to read. It has all the info at the beginning. I have a poor acceleration - low power problem. The ignition timing is retarding instead of advancing. I'm running out of sensors to replace.

I know the timing cannot be adjusted. The distributor is bolted down. It cannot be turned. If a new cam postition sensor is installed, or even any of the other sensors, does the VCM have to be programmed to the new sensor? Does the VCM need to "know" a new sensor has been installed?

Has the problem been found and fixed for this project yet. I am having the same problem and would like to know what the final diagnosis was.

Ive been reading this thread ever since the beggining did you finally take some C4 to it :icon16: or did you get it up and running, im haveing the same sort of prob on my 93 4.3 blazer and am curious to know if you found the answer thanks :smokin:

Has the problem been found and fixed for this project yet. I am having the same problem and would like to know what the final diagnosis was.

No I have not found the problem yet. I did take it to a recommended shop. He hooked it up and relearned the computor for me. He stated that since I had replaced the cam sensor the computor didn't know that. After doing so he ran checks on all the electronics. All the sensors are doing what they are supposed to be doing. He could not check the ECM. i'm down to an ECM. I've been busy and it's getting me around so I havn't been able to do much. I'm going to recheck the compression. It doesn't burn any oil so I think the engine is good mechanically. Sorry it's been so long to get a fix. Thanks for reading.

Ive been reading this thread ever since the beggining did you finally take some C4 to it :icon16: or did you get it up and running, im haveing the same sort of prob on my 93 4.3 blazer and am curious to know if you found the answer thanks :smokin:

It has been a long frustrating summer:banghead: Read previous post for a quick summary. I'm going to recheck compression and probably take it in to a dealer. I've been to 2 dealers and 3 ASE shops. No one can figure it out.runaround
I am the kind of person that will not give up though. I've got too much into it to get rid of it. Body wise the truck is in excellent shape. Thanks for reading and I'll keep everyone posted when I find the solution.

No I have not found the problem yet. I did take it to a recommended shop. He hooked it up and relearned the computor for me. He stated that since I had replaced the cam sensor the computor didn't know that. After doing so he ran checks on all the electronics. All the sensors are doing what they are supposed to be doing. He could not check the ECM. i'm down to an ECM. I've been busy and it's getting me around so I havn't been able to do much. I'm going to recheck the compression. It doesn't burn any oil so I think the engine is good mechanically. Sorry it's been so long to get a fix. Thanks for reading.

That is where I am at. I have checked everything except the ECM. Like you, mine gets me around town. It just drinks the gas though.

I have been reading this for awhile and I really feel bad for you. I am the same, I just can't stop if something is not right, I just keep going and going at it too. I would probably go nuts if I had your situation though, probably would have the engine apart in my garage by now though....

This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.

Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.

If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.

Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.

I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.

How is the truck's charging system? Is the charge/output where its suppose to be?

Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!

I have been reading this for awhile and I really feel bad for you. I am the same, I just can't stop if something is not right, I just keep going and going at it too. I would probably go nuts if I had your situation though, probably would have the engine apart in my garage by now though....

This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.

Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.

If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.

Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.

I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.

How is the truck's charging system? Is the charge/output where its suppose to be?

Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!

Thank you for responding. I have had the truck checked electronically to see if I have a bad sensor. The tech told me that all the sensors are working properly. When I asked about the PCM he couldn't test it.

I did a compression test today. I tested 4 out of the 6. They all had 170 psi. Is that good? I hope that things will slow down for me after the beginning of the year so that I can get it figured out.

I finally found the problem!!!!! The y pipe is double walled. The inner pipe was coming apart on the right bank. I took it to a GM dealer. When he showed it to me he said that it had him stumped. When he removed th O2 sensor on the right side he noticed something inside the pipe. That's when he saw the inside pipe had collapsed!! You cannot see this from the outside. I would imagine most Blazers have this design.

Thank you to all who followed this thread and made suggestions!

If you ever find the cause, PLEASE make sure to post the fix. I also have a 2000 Blazer (125,000 miles) that suffers from relatively low power despite more-or-less everything being new AC Delco parts, good oil and fuel pressure and no codes whatsoever. I can live with mine, but I know the power is not nearly what it should be, and I wouldn't even try to tow with it. I have been monitoring the board for quite a while now, and it seems that there is some problem peculiar to 2000 Blazers that causes this problem -- although I've never seen a solution. Whenever I have seen a "low power" post with no other problems, more often than not it seems to involve a 2000. A somewhat odd sidenote -- a little while after I replaced my lower intake gasket, I ran a quart of block flushing solvent in the crankcase for the recommended number of minutes, drained it and put in fresh oil and filter. During the test drive, it rode like I had installed a supercharger on the vehicle -- the increase in power was beyond incredible -- it seemed even better than when I bought it new. After that, the power gradually decreased over a few hundred miles and went back to "normal" since then, which was over a year ago. I've always changed the oil and filter every 3000 miles from new, so I assumed it was not a general sludge problem. I don't know what any of this means (is there some offending senser that the block flush temporarily cleaned?), or whether it could be related to the problem you are having. But anyway, good luck finding your problem.

I know it took a LONG time to fix it but I finally found my problem. The y pipe is double walled. The inner pipe was coming apart on the right side. I took it to a GM shop and the only way he found it was when he remove the O2 sensor on the right side. He notice something inside the pipe. It was the inside wall fallen out of place and plugging the exhaust. Midas put on a new y pipe for $300.00. Runs like a madman now!!! It is so good to have it running again.!! I hope you get this thread so that you can get you Y pipe checked. Good luck

I too have the same sluggish acceleration problem along with low MPG. At least in my opinion it is low MPG. This is a new vehicle to me so I only have one average MPG reading based on a half tank of gas - 14.5 MPG. However, to be fair this is based on city driving, in sweltering heat 90 to 100 degrees, with the auto temp set at 78. Is 14.5 MPG normal under those conditions? We just put $1800 into general maintenance repairs that included new spark plugs and wires, fuel filter and alignment with tire rotation and balance. We also made some other maintenance repairs, but they would not have any affect on sluggish acceleration or MPG. I have read the other posts but I have no computer readings to compare the performance. There are no codes showing or trouble lights on that would indicate that there is a problem. Is this poor performance or normal for the 2000 Bravada?

Hey- it took a long time but I found my low power problem The Y pipe for the exhaust was coming apart on the inside. It is double walled. It could not be detected by a visual inspection.
The only way it was found was when the technician remove the O2 sensor and found the inner pipe coming apart.

I have been reading this for awhile and I really feel bad for you. I am the same, I just can't stop if something is not right, I just keep going and going at it too. I would probably go nuts if I had your situation though, probably would have the engine apart in my garage by now though....

This has got me thinking two ways, either its running lean/weak as a result of somthing(exhaust restriction), or its a pcm problem. I have a couple of questions, first have you done a compression test on the engine? I'd say you have to make sure you have a good mechanical engine first. Second how is fuel pressure throughout the driving range, have you ever hooked a guage and ran it while your driving. Is it keeping pressure under load? If that checks out, the biggest thing that keeps coming back to me is still a restriced exhaust. I had a similar issue a long time ago with a montana. The vaccuum readings looked good at idle, engine reved alright when on the hoist and in idle, but when you go drive it, it would have no power at all. Engine compression was good, everything looked alright on the scanner but still a no go. I decided to pull the exhaust off, and there it was - restriced exhaust was it, even after a vaccuum guage was on it too. one thing I don't remember on this though was the timing, I don't remember if it had brought the timing back like that.

Timing curve strategies are programmed in the computer. If the engine is timed properly, meaning the timing chain is installed in properly, the distributer is dialed in properly and camshaft timing is within the acceptable threshold, then the engine in general should not be the cause of your problems. It is important the engine is dialed in or you'll just be chasing problems that are not there.

If your ignition system is operating properly, meaning its producing a strong, blue spark at all cylinders, then that pretty much rules the ignition system out too. The ignition system creates spark, the timing of the system is controlled by the PCM as a result of other feedback the system is recieving.

Now what controls timing in itself. Timing is pre-programmed within the PCM, given certain feedback the PCM is reciving as a result of sensor feedback. System load , fuel curve feedback from the 02's, engine temperature etc, all contribute and are calculated by the PCM to achieve the optimum timing stratgies for the engine. Of course feedback is recieved constantly and timing is adjust instantly. Do you notice any difference when the engine is cold as opposed to when its warm? The reason I am asking this is when system is in open loop as opposed to closed loop is there any noticable difference.

I personally cannot see the knock sensors as the issue, because if there was something wrong it would have thrown a fault code and your SES light would be on, assuming of course, you PCM is operating properly.

How is the truck's charging system? Is the charge/output where its suppose to be?

Again assuming a good mechanical, properly dialed in engine, I would probably be chasing the PCM and I would still be looking at an exhaust restriction. Good Luck, and hope you find it soon!

I finally found the cause to my low power. The Y pipe is doubled walled and the inner pipe was coming apart on the right side. The only way the tech found it was when he remove the O2 sensor - he noticed the metal inside the pipe wasn't as it should be. Midas put on a new pipe and it runs great. I bet that this desgn is used on a lot of Blazers. When the exhaust is restricted check more than just the muffler and Cat. Evne if the pipe looks ok on the outside - the inside could still be collapsed.

That is where I am at. I have checked everything except the ECM. Like you, mine gets me around town. It just drinks the gas though.

Read the rest of the thread and check you Y pipe if you are still having problems.

Thats great you got it figured out! Many would have given up on it a long time ago. Internal Y-pipe was restricting it, thats interesting. I knew it sounded like a restriction. Also, more importantly, thanks for posting the solution. At least you can enjoy driving it again...

Thanks for posting back how it went.
Glad you found the problem.
And a good tech that knowed what he was doing.
I have not run to that problem for a long time.
But it goes back to the basic testing to find something like that.
Not many check engine lights or scanners show much there.
Only a good engine capable scanner may have showed a problem wit the 02 sensor.
In your first post we asked for vacuum gauge readings that would have showed a exhaust system restriction.

Good Luck
MT