94 K1500 Random stall crank no start until key is cycled off.

[Throwback67]

I have a 94 K1500 350 TBI auto trans 150k that runs great, but stalls intermittently. When I bought the truck, it ran rough, so I went through it and replaced the cap, rotor, plugs, wires, and cleaned and rebuilt the tbi. It ran better but I had low idle and stalling when coming to a stop and putting it in gear. At this time my first ICM failed and was replaced. Fired right up, but stalling continued. Continued trouble shooting and the low idle stalling, ended up being the distributor. Bought a new ac delco unit and installed it. I also bench tested and replaced as necessary the following items, TPS, IAC, Egr Vac Solenoid, o2 sensor. Replaced Vac Lines. EGR was free and I was able to move it with my finger. During this time, I had my new AC Delco ICM go bad and was causing Intake detonation. Pulled the ICM and realized the factory used almost no thermal paste. Replaced it with one from the old distributor (Oreilley Brand) using some quality thermal paste. Up to this point any time the truck stalled I could shift to neutral and restart while still rolling, also my low idle stalling issue was gone, now my stalling was like I had shut off the key, and happened at all throttle positions, in gear and in neutral, and required me to shift into park and turn the key off to restart. I tested fuel pressure at prime, idle, and under load, and have a steady 9 psig in all scenarios. I replaced all of the Chassis and Frame Cab grounds. I purchased a Bosch Scanner and drove and recorded data multiple times. I was never able to spot any telltale date when the truck shuts off. Everything seems normal, except the random stalling, and now the need to cycle the key for a restart. ECM? I am at a loss...sorry for the long post, appreciate any insight. Thanks,

 

[Throwback67]

Also bench tested coil and swapped with known good coil. Stripped batt cables at side post connector to look for corrosion, replaced temp sensors, both intake and ex man. rewired grounds at water neck,

 

[scott2093]

Sounds like a lot has been looked at although some things seem incomplete in their description. I.e. What happened to idle when you moved the egr with your finger..... what is some of the data ? Coolant temp?..Always good to be specific so there is no doubt.
Maybe you already have your manuals but here are 2 pages from the emissions manual under wonky idle/stalling symptoms.

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

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[Throwback67]

Thanks for the reply. This has been a along drawn out troubleshooting process, and as this is my first tbi engine I dont recall all of the data points. I would look up the parameters for what I was looking at, Ie TPS voltage, and then check RT data with the scanner. When I moved the egr at idle the engine stumbled and died or came close to it. Coolant temp to the ecm was ~200 although The dash gauge is reading around 165 and move around ~10 degrees or so. Based on what I have read on this and other forums the dash gauge is not related to the ecm data?I will hook up the scanner ad take a drive and capture the data and report back. Thanks for the reply.

 

[Throwback67]

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[Throwback67]

The above data is the first frame of a cold start

 

[Throwback67]

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[Throwback67]

The above data is fully warmed up idling in park. Fuel pressure is just above 10 in all driving conditions. I have bee running it all morning in an attempt to get it to stall to see if the ses light comes on after the stall with a spark indicator on the #1 plug. The only exception on the fuel pressure is when I try to restart after a stall the pressure drops off, making me think it is an issue with the fuel pump relay circuit. If I can get it to stall again I will crank it longer to see if the oil pressure switch energizes the fuel pump when the oil pressure comes up. Any help is greatly appreciated. Thanks

 

[Throwback67]

One thing I did notice today is that with the aircleaner off the pcv was pulling so hard it was showing vaccuum at the vent hose coming from the drivers valve cover. It seems like withheld pcv pulling so hard it is essentially an internal vaccuum leak? Pulling ait in from the tbi spacer and into the pcv vaccuum port? Thoughts

 

[Throwback67]

One other thing I recently discovered an hole in my exhaust upstream of the cat and o2 sensor, I don't see how that would lead to stalling, just some more info. Thanks