Our Community is 940,000 Strong. Join Us.


P0300 Codes Got Me


Gabe25
03-31-2008, 02:21 AM
OK, I’m running into a little trouble. Here is the trouble. The almighty P0300 code (Multi-Miss Fire). Here’s what was done.”97” S-10 Blazer, 4.3 Vortec “W” motor. Lower In-take manifold gasket leaking anti-freeze. Radiator pressure test shows 16lbs. After 10 min. drops down to 9lbs. Motor running great. So, I decide to replace the lower in-take manifold gasket this weekend. Toke apart in the in-take and replaced gasket. Waited 24 hours for RTV to set. Mean time I decided to inspect the fuel injector and found that the fuel regulator is leaking, so I went ahead and replaced that as well. Now the 24 hours are up. I started her up and she is missing really bad. Sounds like I’m running a full race cam inside. Which I’m not. Anyway, I went and re-check the distributor to ensure the base line is properly set. No1 DTC full compression stroke. Everything is lined up. Harmonic balancer, timing mark and rotor. Try resetting the distributor one tooth advance and one tooth retard. Both ways no start. I was thinking maybe the harmonic balancer might of shifted. No such luck. So, I went ahead and replace Cap, Rotor, Plugs, and Wires. AC Delco of course. Still no luck. Oh ya, I forgot me mention that I tested the fuel pressure prior to replacing the tune up parts. It was 63 psi and dropped to 57 psi after 20 mins. Fuel pressure remained at 60 psi while the motor was running. Anyway, Still getting the P0300 code and missing bad. Checked EGR valve for carbon. Checked all vacuum lines for leaks. All OK. Checked fuel pulse with noid light. Test OK. Still nothing. Starts and runs rough, still pulling P0300 Codes.

What I’m thinking is the fuel injector housing is crack on the inside and needs to replace the whole assembly.

Any body have any ideas????

MT-2500
03-31-2008, 08:28 AM
I would check the camshaft retard setting.
If over -3 or +3 degrees it can stir up a missfire.
You may need a good engine capable scanner to check and set it.
Also a good scannner will read out what cylinder/cylinders are missing or how many times.
If just one cylinder missing it helps narrow it down.

Fuel pressure does not point to a injector or housing leak.

Can you feel a miss on the road?
Good hot blue spark out of coil and to all plugs?

Gabe25
03-31-2008, 11:32 AM
MT, Thanks. I Checked coil and end of plug wires, and got good blue spark. The scanner that I have is a Auto X-Ray 5000. I'll need to check and see if its able to test the camshaft retard settings. I'm in the office and I everything is at home. So I'll look at when I get home. As far as the miss. Its pretty bad. Like I said earlier. Motor sounds like I'm running a full race Cam on idel. Drove around the block and pretty much no power. Motor feels like starving for gas.

MT-2500
03-31-2008, 12:02 PM
You are welcome and double check the plug wire firing order.
or remove one plug wire at a time to find missing cylinders.
Good luck and let us know how it goes.
MT

Gabe25
03-31-2008, 01:54 PM
MT, I just was wondering about the cam shaft positioning sensor inside the distributor. Could this be causing my trouble? I just throwing ideas around in my head.

MT-2500
03-31-2008, 07:23 PM
MT, I just was wondering about the cam shaft positioning sensor inside the distributor. Could this be causing my trouble? I just throwing ideas around in my head.

It should set a code.
I had one go bad but it had a code and camshaft retard setting wws way off around 35-45 degrees.
Try running a cylinder balance test or remove one plug wire at a time and see if any cyylinders are dead /missing.
Good Luck
MT

Gabe25
03-31-2008, 10:11 PM
It should set a code.
I had one go bad but it had a code and camshaft retard setting wws way off around 35-45 degrees.
Try running a cylinder balance test or remove one plug wire at a time and see if any cyylinders are dead /missing.
Good Luck
MT
MT, OK I pulled one plug wire at a time and each time it ran worst. Re-checked firing order, and thought I had No. 1 & No.3 cross, but no chance. Working on getting a good scannner that will read out what cylinder/cylinders are missing. Although it seems like none of the cylinders are missing. Will update later.

MT-2500
04-01-2008, 10:53 AM
Double check for vacuum leaks and you might try pluging the egr valve port at intake.
Good luck and let us know how it does.
MT

Gabe25
04-01-2008, 11:59 AM
Double check for vacuum leaks and you might try pluging the egr valve port at intake.
Good luck and let us know how it does.
MT
OK, I sprayed all the vacuum lines with carb cleaner and pulled the ERG and rechecked and cleaned. All looks good, no leaks and no carbon. Plunger move freely. I'll be bring home a Snap-No engine Diag tester tonight and run a complete diagnostic. I should be able to take over my on board computer and pull complete graphs of everything. We'll see what happens.

Gabe25
04-02-2008, 12:18 PM
Still on going. Got home to late after after picking up the engine diag scanner. Then again I think it mite of been to many Crown Royals on the rock that made it to late. Anyway, I hope to finish this saga sometime today. Will keep you posted.

MT-2500
04-02-2008, 01:03 PM
Good luck and let us know how it goes.

Gabe25
04-02-2008, 09:58 PM
OK, Just finished the testing. The scanner is coming up with misfiring in cyliners 4 & 5 at about 30%. Now I'm total lost. I tried looking in my manuals on how to trouble shoot this type of trouble and found nothing. Are there any words of wisdom out there.

16th hippy
04-02-2008, 11:21 PM
while you were spraying the vacuum lines and such, did you happen to spray the intake around those areas? might have a gasket leak there too. sounds fishy having misfires on both banks. just a thought.

MT-2500
04-03-2008, 01:14 PM
A couple of things to check.
If you still have the scanner try the injector balance test.
Also check the injector plugin on top of intake and make sure it is pushed on and locked down good.

Cylinders 4 and 5 are right next to each other in the firing order.
Look the new dist cap over good and double check camshaft retard setting.

Also on 96-97 4.3 engines there is a tsb on o2 sensor wiring that can cause missfire or misfire codes and or 02 sensor codes.
Check the wiring and plug in for moisture or green stuff.
The moisture can get into the wiring at the starter area/plugin to the 02 sensor wiring.
TSB no. 77-65-12 april 97
Good luck
MT

Gabe25
04-03-2008, 03:24 PM
A couple of things to check.
If you still have the scanner try the injector balance test.
Also check the injector plugin on top of intake and make sure it is pushed on and locked down good.

Cylinders 4 and 5 are right next to each other in the firing order.
Look the new dist cap over good and double check camshaft retard setting.

Also on 96-97 4.3 engines there is a tsb on o2 sensor wiring that can cause missfire or misfire codes and or 02 sensor codes.
Check the wiring and plug in for moisture or green stuff.
The moisture can get into the wiring at the starter area/plugin to the 02 sensor wiring.
TSB no. 77-65-12 april 97
Good luck
MT
MT. When I scaned last night. I ensured that I do a complete total diag on everything. That included the injector balance test. I when as far as shuting down one injector at a time to see if there was any difference in the idle. Of course after each shut down I needed to restart the motor. I did a spark plug swap out to see if the misfiring cylinders would move. Plug 1 to 4 and Plug 2 to 5. No such luck. Still misfire in cylinders 4 & 5. Will continue again after work. Thanks for all your help. I'll keep you posted.

MT-2500
04-03-2008, 05:01 PM
Some place in the snapon scanner there is a injector balance test you can do with engine off and with a fuel pressure gauge hooked up to watch how much fuel pressure dropem with injector on a certain amount of time.

On The 02 sensor wiring tsb I posted I had only one blazer that done it.
It had a dead miss on one cylinder.
That I finaly got out by moving the wiring around and switching and unpluging and pluging back up 02 sensors.
If you can find the wiring plug in on the 02 sensor wiring harness you might try unpluging it and see if miss goes away.
Not sure that is your problem but I had one that done it big time.
Drove me ragged trying to find it.
If you want the TSB on it e mail me and I will pdf it to you.
Good luck.
MT

MT-2500
04-03-2008, 05:01 PM
Some place in the snapon scanner there is a injector balance test you can do with engine off and with a fuel pressure gauge hooked up to watch how much fuel pressure dropem with injector on a certain amount of time.

On The 02 sensor wiring tsb I posted I had only one blazer that done it.
It had a dead miss on one cylinder.
That I finaly got out by moving the wiring around and switching and unpluging and pluging back up 02 sensors.
If you can find the wiring plug in on the 02 sensor wiring harness you might try unpluging it and see if miss goes away.
Not sure that is your problem but I had one that done it big time.
Drove me ragged trying to find it.
If you want the TSB on it e mail me and I will pdf it to you.
Good luck.
MT

Gabe25
04-04-2008, 12:24 PM
Thanks MT, Got the serive Bulletin. I tried the fuel balance test with the pressure gauge, but had to stop. My pressure gauge decided to spring a leak. It was old so I'll pick up a new one today and continue. Anyway, Tried spraying carb cleaner around the upper Plenum looking for possible cracks. Still nothing. I drained the gas and replaced it with fresh gas and bleed the fuel lines, and still nothing. This blazer is my sons and I was thinking mybe he bought some bad gas. It was just a thought. Anyway, I'll continue again tonight after work and hope to get her running by this weekend. Will let you know. Thanks again.

Gabe25
04-06-2008, 10:43 PM
OK completed the fuel injector balance test with my new fuel pressure gauge and everything tested OK on all the injectors. :banghead: Now, I remember before reading somewhere that someone was having trouble with there idle and it turned out to be a ground strap from the firewall to the engine. Anybody heard anything like that. This trouble has really got me thinking. :screwy:

Gabe25
04-08-2008, 03:43 AM
OK, the saga continues. So far I’ve replaced the following:
1. Lower Plenum Gasket Set (Leaking Water)
2. Spark Plugs ( Burning OK)
3. Cap (Little Worn)
4. Rotor (Small Carbon)
5. Wires (Uneven Resistance)
6. Cam Positioning Sensor
7. Coil (Weak Reading)
8. Injector Fuel Regulator (Leaking)

Testing performed:
1. Fuel Pressure.(62psi)
2. Leak Down 20 mins. (59psi)
3. Fuel injector Balance test. (All passed)
4. Fuel Pulse test. (All passed)
5. Cylinder Compression Test (All even)
6. Blue spark at end of plug wire
7. Triple check #1 is TDC
8. Distributor set on #6, Firing order #1.

Trouble is still there. P0300 Code. Multi Cylinder Missfire. Cylinders 4 & 5. I had one more thing to check. O2 Sensor, which I’ll be testing tomorrow. Does any body out there have any ideas. I’m kind of running out of them.

MT-2500
04-08-2008, 11:02 AM
Gabe
Just a few things I casn think of to recheck or check.
Did you set the camshaft retard setting on the scanner?
Does scanner show lean fuel trims?
Can you feel a dead miss on the road?
Does pulling no 4 or 5 plug wire affect it any?
Have you double checked the injector plug in?
Liked locked down good and tight?
Is it getting injector pulse on 4 and 5 cylinders?
Does unpluging mass air flow sensor make any difference?
Good luck
And hang in there.
MT

Gabe25
04-08-2008, 02:27 PM
MT, Thanks for the ideas. Here is the answer:

Did you set the camshaft retard setting on the scanner?
Yes
Does scanner show lean fuel trims?
Yes
Can you feel a dead miss on the road?
Yes
Does pulling no 4 or 5 plug wire affect it any?
Yes
Have you double checked the injector plug in?
Yes
Liked locked down good and tight?
Yes
Is it getting injector pulse on 4 and 5 cylinders?
Yes
Does unpluging mass air flow sensor make any difference?
No: When pulled. Only Error code for Mass Flow comes up. Reinstall and error clears

Gabe25
04-09-2008, 01:28 AM
MT, Do you know what the voltage reading should be on the injector pulse? I cleaned the MAF screen wires. They were full of carbon, but no change on misfire. Still searching.

16th hippy
04-09-2008, 03:07 AM
one side is constant power(battery voltage). not sure if it grounds when vehicle is off/not running.

the other is the ground controlled by PCM/ECM to fire it.

MT-2500
04-09-2008, 08:56 AM
MT, Do you know what the voltage reading should be on the injector pulse? I cleaned the MAF screen wires. They were full of carbon, but no change on misfire. Still searching.

As 16th said.
One side is 12 volt positive key on.

They trigger off of a ground side pluse.
The PCM controls the ground pulses the ground signal width engine running or cranking.
The pulse width sometimes can be read on scanner.
You will need a lab scope to measure the pulse width.
MT

Gabe25
04-12-2008, 03:30 AM
The Final Chapter comes to an end. This has to be one for the books. After going through all of this testing. It comes down to fuel injector 4 & 5 tubes are pluged. Gas was being restricted. I was going to attempt to open them up and clean them out, while removing it from the lower Plenum. Injector tube number one broke. With that, I just said the hell with and picked up a new CPI Unit. Slamed it in and my son is smiling.
MT & 16th. In Hawaii we say Much Mahalo for everything. Which means Thank You Very Much for all of your help. Have a great Weekend. I know I will. Off to the Beach.

MT-2500
04-12-2008, 08:26 AM
You are welcome and thanks for posting back how it went.
Glad all is well and fixed.
Enjoy the beach.
We may get some snow today here in Mo. USA.
Good luck
MT

Add your comment to this topic!