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4.3 CPI Stalls in gear


Sinful7
11-11-2007, 07:44 PM
-'92 Bravada, 4.3 CPI (W), idles fine, but dies shifting to drive.

-New trans.
-Newer motor.
-New CPI spider.
-New ign, incl. ign module.
-New exhaust (downpipe back, incl cat, not O2 sensor).
-Stalls when I shift into RD12.
-Runs when I'm in P/N.
-Vacuum leaks tested by blocking the intake with my hand. Engine stalled as it should.
-Will maintain idle in gear if I depress the accelerator.
-Will maintain idle in P/N when A/C and Alternator are loaded.

I've searched all over and have seen this complaint a lot, but all threads lack real resolution. I'm considering the IAC and the TCC, but the testing procedures listed in the FSM are a bit convoluted and I already gave myself a 120kV shock testing IAC operation per the FSM, so I'm not too certain it knows what it's talking about, lol!

TIA

blazes9395
11-11-2007, 07:59 PM
Does it stall right away, or does it chug and stall. It could be either of those two things you mention, it could be an EGR valve. Was the timing ever dialed in when the engine was replaced? Was the base idle ever been tampered with?

Sinful7
11-11-2007, 08:44 PM
Does it stall right away, or does it chug and stall. It could be either of those two things you mention, it could be an EGR valve. Was the timing ever dialed in when the engine was replaced? Was the base idle ever been tampered with?

Here's the whole story:
I was driving at hwy speeds when suddenly my motor died. Towed the truck home and replaced the ign module. Truck started, but died in gear. Went out and bought a new car that night, but this problem has plagued me for a year, lol.

The car stalls almost immediately. RPM's drop, leading to a stall without hesitiation. Timing is properly adjusted (unplugging the timing advance plug before setting). Adjustment of timing +/- results in no net effect. Base idle has never been adjusted, though I've been tempted to twist the screw a tad to see what happens!

The problem initially resembled a failed ign module, but I think the original cause of the motor dying was a combination of the ignition and some other issue.

The emissions controls have 216,514 miles on them, except the PCV.

old_master
11-11-2007, 08:51 PM
Fuel delivery is critical on CPI systems. Check the fuel filter, fuel pressure, and check for excessive leakdown. Post your results.

Sinful7
11-11-2007, 09:22 PM
Fuel delivery is critical on CPI systems. Check the fuel filter, fuel pressure, and check for excessive leakdown. Post your results.

Leakdown is minimal. Pressure is 60PSI and holds steady after shutdown. Fuel pump, inline and in-tank filter are new and clean (less than 10,000 on each). The vehicles displays no indication of fuel delivery problems (no surging, no rough idle, no smell, no [new] discoloration in the the plenum. Idle exhaust output may be a little rich, it's tough to tell because the vehicle is backed into the garage. Also the exhaust smell may be exacerbated by an idle problem.

Tomorrow I'll remove and clean the EGR and post results. I will also try to remove the TPS and see if it's sticking or in need of cleaning.

The fact that it dies without hesitation when put into gear leads me away from fuel problems. Also the engine runs at full speed no load without problems.

Sinful7
11-11-2007, 09:33 PM
By the way, thanks for all the help! I try to open-talk about vehicle diagnoses with my buddies, but they give up after "Does it have gas?"

Sinful7
11-12-2007, 08:40 PM
TPS was clear and free. My multimeter died, so I was unable to test resistance on the unit. After cleaning that, I decided to see if it would throw a code just for sh*ts and grins.. It didn't trigger an SES, but nevertheless.

Low and behold, I got an SES code! #42 (EST-Electronic Spark Timing unit faulted to ground).

I'm not 100% on how to double-check this code. I started the engine, no SES light. I shut it off, cycled the ign on/off 10 times, shorted the ALDL connector and it presented the same code. I know I could clear the memory by unplugging the battery, but 2 things kept me from this: 1) the truck sat ign-off all night and day (24 hours), and 2) my alarm siren blares when I reinstate power. My neighbors have babies that probably are heading to bed, so I considered them and didn't disconnect power.

I guess I'm gonna dig up my recepit for the EST unit from Advance and see if it has remaining warranty.. If so, I'll just exchange it and try starting again!

Thoughts??

TIA

donwkk
11-12-2007, 09:17 PM
You can clear codes by pulling the ecm fuse for about 10-15 seconds. Look in owners manual to identify ECM fuse or diagram may be on fuse box cover. Sittig 24 hours will not clear codes nor will turning ignition on and off. The computer is programmed to turn codes off after a certain number of starts and/or run minutes if fault no longer exists. Good luck.

Sinful7
11-12-2007, 10:02 PM
Haha, found that one out the hard way.. I replaced the EST to no avail. A couple new notes:

-Excessive exhaust smell (rich).
-Vehicle starts and goes into Drive when cold.
-Vehicle dies when in park and warm and steering is dry-turned.
-Post-EST replacement, vehicle starts and goes into drive with throttle assistance, but idles only briefly (sub-15 seconds) before dying.
-Vehicle moves in forward and reverse under light throttle


Now that I think about it again, the EST code was probably due to me pulling the EST advance wire when timing the motor again yesterday.

Tomorrow I'll remove the plenum and EGR. How do I check for proper EGR operation? Is it possible/recommended to permanently bypass the EGR without throwing codes?

Steve

randolphtpr
11-13-2007, 08:19 AM
When Mine Did This I Got A Temperature Sensor Code....there Are Actually Two....one For Your Gauge (sender) And One For The Computer (sensor)...the Sensor For The Computer Was At Fault....after New Cap And Plugs ....and The New Sensor It's Perfect...it Was A Code 15....i Did Not Know What Havoc That Thing Plays With The Fuel Injection System

blazes9395
11-13-2007, 09:16 AM
The EGR on these trucks with this engine (W) is digital. If you disconnect it, it will soon set the SES light.

How is the engine mechaniclly? Has compression ever been checked? How is the vacuum. Have you ever checked the base idle on the engine?

Unplug the EGR and leave it and start it, see if that does anything to it. From there, I would check base idle and see if its withn acceptable range.

Also like randolphtpr mentioned, it might be a good idea to get a scanner and see what the sensors are doing, something might pop up.

Sinful7
11-13-2007, 07:12 PM
Bah, before I jump into just pulling every sensor, I'm going to follow your advice and rent a scantool. I'll post any unusual result.

Also, through investigation of the FSM, I've found this regarding the P/N switch:
If CKT 434 is open in Park, Idle will drop when transmission is shifted into drive.
Sounds kinda like what I'm experiencing.. except my vehicle dies when in park and the wheel is turned.

I'll try to get the scanner tonight and check it out.. Let you know what I find!

Sinful7
11-13-2007, 07:14 PM
When Mine Did This I Got A Temperature Sensor Code....there Are Actually Two....one For Your Gauge (sender) And One For The Computer (sensor)...the Sensor For The Computer Was At Fault....after New Cap And Plugs ....and The New Sensor It's Perfect...it Was A Code 15....i Did Not Know What Havoc That Thing Plays With The Fuel Injection System

Something I wouldn't have thought of! Great advice! I've got no SES light, and no other stored codes, but I'll see if the scantool provides insight.

Sinful7
11-13-2007, 09:29 PM
Okay.. well it appears that the 'scan tool' I rented is simply a code reader.. which is retarded since I can pull codes from the SES indicator. (Incidentally there were no codes stored.) It won't actually provide sensor outputs. For that I need the $1500+ Tech 1 scan tool from Vetronics or other providers. Meh.

I guess I'll have to go buy a new multimeter and ohm out the sensors. Too late for that tonight so I'll hit RadioShack on the way home tomorrow.

Sinful7
11-13-2007, 09:39 PM
How is the engine mechaniclly? Has compression ever been checked? How is the vacuum. Have you ever checked the base idle on the engine?


Also on this note, I'm curious that if the engine was mechanically failing, would the problem only present when the engine is warm? The truck will shift into drive and idle fine until the engine reaches a minimal operating temperature. It seems to me given that, the problem must be related to emissions control equipment and/or monitoring that is only active when the ECU goes into closed-loop mode?

Sinful7
11-13-2007, 10:48 PM
Ooookay... So tonight's diagnoses provided a potentially interesting symptom change:

-The vehicle will maintain idle indefinitely in gear when the EST (Electronic Spark Timing) wire is unplugged thereby preventing EST adjustment.

-The vehicle will idle in gear from startup until the temp gauge has reached 200 degF.

From reading the FSM, it says,

"Controlled idle speed is always specified for normal operating conditions. Normal operating conditions are: coolant temperature in normal operating range, the A/C OFF, auto trans in Drive."

I'm wondering now if the IAC is stuck? Should I be able to manipulate IAC position by hand? How far out should the IAC pintle be when it's fully extended?

I wish a dealer service was in the budget.. Bah!

randolphtpr
11-16-2007, 07:55 AM
broken record.....temperature sensor.....only $17 and 15 minutes.....it just sounds so similar to my symtoms....a cap and rotor and replacing the soaked spark plugs didn't hurt.....your temp gauge can read normal but the other temp sensor may not be working....it's right down by the egr...

Sinful7
11-16-2007, 12:46 PM
broken record.....temperature sensor.....only $17 and 15 minutes.....it just sounds so similar to my symtoms....a cap and rotor and replacing the soaked spark plugs didn't hurt.....your temp gauge can read normal but the other temp sensor may not be working....it's right down by the egr...

Ok, I'll give that a shot. I thought a temp sensor would throw a code or something. I also found a dude on eBay selling the IAC, TPS, EGR and MAP for $29.99 so I hit that just in case! I'll replace the temp sensor tonight and report back!

old_master
11-16-2007, 04:04 PM
The ECT sensor will not set a DTC unless it's output is out of range. It's entirely possible for it to be out of calibration and still be within range.

If the ECT indicates a lower than actual temperature: The ECM "assumes" the ECT is indicating the correct temperature provided it is not out of range. The ECM will adjust fuel mixture, idle speeds, etc etc, based on the signal it receives from the ECT.

Sinful7
11-16-2007, 05:05 PM
Well, the ECTS is replaced with no effect. Good idea though!

I just really hope this isn't a short in a sensor wire.. that would suck. Hopefully shortly I'll be getting some used emissions controll equipment that I can try swapping out. If I get time soon, I'll remove and clean the EGR. To be continued!

randolphtpr
11-17-2007, 09:21 PM
geez....what is the idle speed now???....this is another notion i thought was my problem .....i checked vacum at the brake booster and thought for a second that maybe the booster leaked....it was not the case but it was something that never occured to me...brakes ok???......what about a neutral switch either shifter or tranny???....my God man....what have you got....?

Sinful7
11-18-2007, 02:19 PM
geez....what is the idle speed now???....this is another notion i thought was my problem .....i checked vacum at the brake booster and thought for a second that maybe the booster leaked....it was not the case but it was something that never occured to me...brakes ok???......what about a neutral switch either shifter or tranny???....my God man....what have you got....?

LOL! Yeah, hence bringing forth the problem to the community.

I guess I haven't measured the vacuum yet, but I have conducted the 'spray test' with carb cleaner to find any leaks around the upper plenum and attached lines.

I also don't have a very precise tachometer- just the one in the digital dash. I've had this truck for 14 years though, and I would know if something sounded amiss.. Nothing does.

randolphtpr
11-18-2007, 04:55 PM
i'll keep checking in but i'm at a lose right now...sorry....you have me going though and thanks for that..

Sinful7
11-21-2007, 03:34 PM
Last night I replaced the IAC to no avail. I'm gonna head out to the garage and try replacing the egr.

randolphtpr
11-21-2007, 09:56 PM
oh please let that be it...i think the egr would make it act the way it has been...i'm praying for ya!....it will be a nice thing to be thankful for...please post results

Sinful7
11-23-2007, 08:53 PM
Unfortunately I have not had an opportunity to check/clean/replace the EGR since my last post. (I'm on night shift all week and my sleep patterns are all whacked) I did however, manage to remove the UIM/Plenum and observed not only washing in the RH dish, but also a small puddle of oil within the plenum interior!

Now, I'm not really sure how this oil got in there as the area should be sealed of by the plenum gasket. I'm also not certain the washing is indicitive of a fuel pressure regulator failure - I've replaced the CPI Spider thrice in the past years, and I've never seen a re-accumulation of carbon on the RH side.

Next item up for replacement is, of course, the EGR. However I will also attempt to R&R and clean the spider ball valves and recheck the fuel pressure stability.


One more observation of interest - When I replaced the IAC, the new pintle was fully extended. After flunked testing of the replacement, I removed the IAC to check its position and found it to fully retracted. This obervation, combined with previous (that opening the TB allows the engine to run), tells me that the ECU is indeed attempting to control the idle and is simply unable to adjust the A/FR appropriately.

old_master
11-23-2007, 08:59 PM
Fuel on the passenger side indicates a leaking fuel pressure regulator. Check back to post #4... Check fuel pressure and leakdown when the engine is cold. Pump running engine off pressure must be 60 to 66psi. After the pump shuts down, pressure must remain above 55 psi for 3 to 5 minutes.

Sinful7
11-25-2007, 04:39 PM
Fuel on the passenger side indicates a leaking fuel pressure regulator. Check back to post #4... Check fuel pressure and leakdown when the engine is cold. Pump running engine off pressure must be 60 to 66psi. After the pump shuts down, pressure must remain above 55 psi for 3 to 5 minutes.
OK! I finally had a second to check the FPR and EGR:

FPR-
Pump running - 61ish PSI.
Pump off - 57 PSI.
3-5 Min Leakdown - 55PSI (holds steady indefinitely, I watched it for 10 mins).

I performed the leakdown test three times. The first time, I got 61/57/54. The second time I didn't relieve fuel pressure prior to testing and I got 61/57/57. The third time I did relieve fuel pressure to yield the above results.

EGR-
No visible blockages.
Valve moves freely, no reason to suspect clogging or failure. Clean and reinstall.


EDIT: After I posted this, I went back out to the truck to compare the EGR movement with the used replacement EGR I have and to visibly inspect CPI poppets to confirm none are stuck open. None were. For sh*ts and grins I flipped the ign on to check the FPR one more time- a true 'cold test' as I've let it sit for more than 5 mins a 0 psi. The result was:
Pump on- 61PSI
Pump off- 57PSI
5 Min leakdown - 52PSI.

Is it possible I'm experiencing an intermittent FPR failure? Are my testing procedures above just incorrect?

I'm considering ordering the Linder Tech FPR replacement. Anyone have experience with this product?

old_master
11-25-2007, 06:15 PM
Fuel pressure is good, the regulator is what determines the 61psi that you have been getting. It is not adjustable, whatever the spring pressure is in the regulator...that's the pressure you'll get. The (cold) leak down you're experiencing is very small...and will be difficult to pinpoint. The fact that it leaks does not tell you where the leak is, only that there is a leak. To determine if the problem is the pump, regulator, or an injector, you need to isolate the fuel pump after the system is pressurized. The only way to do that is with a shut off valve installed in the fuel pressure line between the fuel pump and the pressure test port. After the pump pressurizes the system, shut off the valve and watch pressure for leakdown. If it holds, the problem is the fuel pump, if it drops, the leak is under the plenum.

Sinful7
11-25-2007, 07:05 PM
Argh! The very last thing I want to replace it the fuel pump, yet again.

Let me see what I can come up with for a FP shutoff valve.

randolphtpr
11-28-2007, 08:57 PM
what would happen if you left the fuel pressure gauge hooked up and observed what the pressure did when the engine was running and shifted...i would say from your results the fuel pressure and delivery is well within the limits to function....just a shot in the dark but there must be some kind of neutral saftey switch...it could be part of the shifting and key business in the column...i have to know what this is...please keep posting

old_master
11-29-2007, 06:21 PM
No problem leaving it connected to watch as a reference only. GM does not publish any specification for fuel pressure while the engine is running.

randolphtpr
12-07-2007, 05:19 PM
do you have these vac lines...check out this link for tranny vac lines...does vac check out???
i'm still thinking on this one....any news????


http://www.automotiveforums.com/vbulletin/showthread.php?t=498411&highlight=vacuum

Sinful7
02-21-2008, 02:42 PM
Well, I've still been wrestling with this problem, I have yet to pinpoint an answer. Thus far, I've replaced just about everything on the top end, save for an additional spider replacement.. The conditions just aren't indicative of spider failure.

I'm wondering now, how does the engine know to increase RPM to compensate for additional load when the transmission is put in gear?

old_master
02-21-2008, 04:58 PM
The ECM receives a signal from the neutral safety switch when you shift in or out of park/neutral. The ECM increases or decreases RPM as necessary. Same with the AC compressor when you turn on/off the AC or defrost.

Sinful7
02-21-2008, 05:20 PM
Through the diagnosis I initially performed, aided by the FSM, I primarily considered the PN switch to be the culprit. I think I'll start tearing into that bad boy tomorrow. Is that located in the steering column?

(Posted from my Blackberry)

old_master
02-21-2008, 05:22 PM
It's mounted on the transmission, the shift linkage goes through it.

s10manic
02-21-2008, 06:40 PM
i might also recommend that you check the MAF Sensor if you havent already

Sinful7
02-21-2008, 07:12 PM
i might also recommend that you check the MAF Sensor if you havent already

Thanks for the suggestion. It's actually a MAP sensor, and I've checked it.

Sinful7
02-22-2008, 01:00 PM
It's mounted on the transmission, the shift linkage goes through it.

The only P/N Safety switch I can find in the FSM is located on the steering column. Is there another thing I should be looking for? This is a 4.3CPI with a 4L60.

old_master
02-22-2008, 02:20 PM
If you're using a FSM, (GM factory shop manual) for the correct year vehicle, it will tell you exactly where it is. If you're using a Chilton or Haynes repair manual, there's no telling what they say, they're just about worthless. If it's not on the transmission where the shift linkage attaches, it's probably on the steering column.

bearcat58
02-22-2008, 02:29 PM
Did you ever get this problem resolved? I have the same problem with an older chevy.

Sinful7
02-23-2008, 04:17 PM
Nope, still hitting it. I was studying a wiring diagram for the P/N switch and discovered that when it's closed (in P or N), it supplies a ground to the rear gate glass. The glass will not operate in any gear or reverse, so the switch itself is functioning. Now I'm suspecting the culprit is either a seperated wire to the ECM or a bad ECM. I've had to replace it (the ECM) once before, so I kinda hope that's not it.

Sinful7
08-12-2010, 10:15 PM
Not to bring random dead threads back to life, but it's been three years and I'm finally getting back around to digging at this problem.

After a rebuild from the long block up, I'm certain that there's no leaks and everything is running correctly (except the idle).

So far, I've done-
(2) Knock sensors
Coolant temperature sensor
Ignition control module
Fuel filter
Fuel pressure test - 60PSI on, drops to 58 PSI when idling in park. Leakdown- pressure drops to 52 PSI after 30 minutes.
Electronic Spark Timing (ICM) test

Along with the mechanical-
Upper plenum gasket
Lower intake gaskets
Rocker cover gaskets
PCV
Crankcase breather filter
Hand cleaned UIM, LIM, heads
E-Fan Conversion

It started right back up and ran rough for a day, then I think the ECM regained consciousness and the idle characteristics evened out.

So, it's back to starting and idling fine in Park, but it dies in gear when the engine is warm.

-If I unplug the 'bypass' wire for the electronic spark timing, the engine idles in gear, just like it should... Does that perhaps indicate a bad distributor pickup or ECM?

I may just hobble this thing down to my nearest GM indy shop... three years and $100's in replaced parts to no avail- I just hate the thought that this CPI POS beat me...

Sinful7
08-14-2010, 10:38 PM
-If I unplug the 'bypass' wire for the electronic spark timing, the engine idles in gear, just like it should... Does that perhaps indicate a bad distributor pickup or ECM?

Well, it's not the pickup coil.

I unplugged the MAP sensor and re-plugged it, and the engine will crank and start, but won't hold. Now I'm beginning to suspect a fuel issue... argh. I'm taking this thing to a shop Monday for a bit o' diagnosis... heck, it's only been three years... think of all the money I've saved not driving it during that time! :-)

I'll be sure to post whatever the problem ends up being. This has been a total 'ghost' problem - all the sensors and controls check out, all of everything is functioning fine, even fuel pressure. Hopefully what I learn can be googled by others after me.

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