4.3 CPI Stalls in gear

[Sinful7]

-'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]

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]

Originally Posted by blazes9395

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]

Fuel delivery is critical on CPI systems. Check the fuel filter, fuel pressure, and check for excessive leakdown. Post your results.

[Sinful7]

Originally Posted by old_master

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]

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]

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]

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]

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]

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]

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]

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]

Originally Posted by randolphtpr

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]

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]

Originally Posted by blazes9395

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?