1990 Suburban dies intermittently

[SoCalSlaughter]

Hey guys, my truck is a 1990 Suburban V2500 5.7-TH400. Ive been having an intermittent problem of the truck just dying while at lights or stop signs. The truck has a very loud whistle I have found out is the IAC, the whistle will stop if I stick i finger down the air passage. The gas millage also has decreased. The truck will randomly through codes 13 (O2 sensor) and 42 (ECM has lost communication with the distributor). The code 13 with turn on, but once I start driving it will turn off. And the code 42 usally sets when im at a stop for a long period of time, the light will come on and the idle will drop. This has been driving me crazy. Ive tested and replaced everything but the engine. haha Still cant find the problem. The truck also, when at lights will lurch forward sometimes, or the rpm will just kick up and the whistle will get louder, but once I shut the truck off, and start it back up, it will run fine.

[SoCalSlaughter]

Also, I removed the ECM the other day to inspect the wiring and noticed it was hot. Could this be connected to my problem? The ECM is new, less then a year old.

[SoCalSlaughter]

So today I removed the entire wiring harness from the engine bay, inspected ever inch of the wiring and couldnt find a pinch, or exposed wire. Installed the harness again, and after about 10 miles, the light came on again..

[Greenlee]

I found the following info for Code 42:

Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system. During cranking, the timing is controlled by the ignition module and the ECM grounds the EST line. It expects to see no activity on this line at this time. When the ECM enters EST mode, it applies +5 volts to the BYPASS line and expects to see voltage variations on the EST line.
Reasons for the ECM to set Code 42:
? System in BYPASS mode (i.e. EST line supposedly grounded) but activity sensed on EST line
? System in EST mode (i.e. BYPASS line driven with +5 volts) but no activity seen on the EST line

Possible causes include:
1. BYPASS line is open or grounded
2. EST line is open or grounded
3. Poor connections between ignition module and ECM
4. Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise
5. Faulty or incorrect ignition module
6. Faulty ECM

I have a similar issue where mine will sometimes start to idle rough at a stoplight. It usually won't die, but it has died before. However, I'm not getting any codes. I'm running the wire harness and drivetrain from a 89' Suburban.

[SoCalSlaughter]

Thanks for the reply. Ive replaced the ECU, the ignition module (Multiple times) Ive replaced the pig tail that plugs into the ignition module, pulled the wire harness off and re wrapped with electrical tap. Ive replaced the entire distributor. I cannot figure this one out, its been driving me crazy. Ive even cleaned and moved the ECU ground to 3 different places to see if it had a bad ground, but no difference. Only possible thing I could think of doing now is finding a pin chart of the ecu and running my own wires to the control module. Ive been doing this since 2008.

[Zeke's Garage]

Did you fix the issue with the IAC? It should close completely on warmup, and there should be no whistling. As for erratic idle and engine shutoff, I've had issues with bad or stuck EGR valves causing this problem. You may want to verify that it's closing all the way, and not causing an idle issue that the IAC is trying to compensate for.

<Edited once I realized that you already checked your grounds and ignition module.>

But, did you check the sensor grounds on the front of the manifold?


Good luck with it

Shawn

[Dale99]

I will say pull the TB off, and clean the IAC and its passages. Be careful not to spin the tip of the IAC while its out.

A stuck open IAC will cause stalling and whistle.
Open EGR can cause the O2 sensor to read rich and cause codes(possible whistle as well).
code42, you also have whats called a pickup coil in the distrib, its basically a bunch of wound up copper wire. I have heard of them going bad... not often though.