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

[Throwback67]

Unplugged the fuel pump relay while running and it continued to run. Oil pressure switch is operating correctly.

 

[Throwback67]

Just crawled under the truck and the exhaust hole is down stream of cat and o2 not upstream soooo....

 

[Throwback67]

I also pulled the glove box and did the mallet test on the ecm, no change. If it were me driving it it wouldn't be an issue, but it is my sons truck and he is a new driver. I can't have random stalls with him driving. Any and all help and ideas are greatly appreciated.

 

[Schurkey]

94 K1500 350 TBI auto trans

stalls intermittently... ...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.

Need to verify IAC operation.

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.

HOW do you know it was "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

Repeat ignition module failures are often due to a failing ignition coil.

and was causing Intake detonation.

"intake detonation"? You mean "backfiring into the intake manifold"?

Intake backfires are generally caused by
1. Lean air/fuel ratios
2. Burnt/leaking intake valves or valve seats.

Consider cranking compression test on all eight cylinders, and perhaps cylinder leakdown testing.

Pulled the ICM and realized the factory used almost no thermal paste.

Doesn't take much.

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.

Verify power to ignition coil--and from there to the ignition module.

This is starting to sound like poor connections in the ignition primary circuit...or a failing ignition switch.

I tested fuel pressure at prime, idle, and under load, and have a steady 9 psig in all scenarios.

Theoretically acceptable. Most folks would want to be at the higher-end of the spec.

I purchased a Bosch Scanner

I'm not familiar with them. What is "LT Fuel TR CL" and "LT Fuel TR EN"?

The O2 crosscounts are startlingly high especially on an engine that's only run for 29 seconds. Do you have a heated O2 sensor?

Also bench tested coil

HOW? Ohmmeter tests of primary resistance, secondary resistance, and windings-to-ground?

Did you use a spark-tester calibrated for HEI to determine voltage capacity?

An ohmmeter can tell you if an ignition coil is BAD. It cannot tell you that it's good.

replaced temp sensors, both intake and ex man.

There is no temp sensor in the exhaust manifold. Do you mean "cylinder head"?

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?

It's a matter of degree. Of course the PCV system pulls a vacuum on the crankcase, which draws fresh air in from the TBI spacer, through the hose, to the valve cover opposite the PCV valve.

But if the PCV valve is incorrect or failed, you may have excessive vacuum in the crankcase, leading to "more" of an air-leak into the engine that the system is calibrated for. (i.e., it is a vacuum leak, and the engine control system is designed to accept a certain leakage of air into the intake manifold via the PCV system.)

Wild Guess with no evidence: The vacuum you're seeing at the TBI spacer is normal.

 

[Throwback67]

#1 I no longer have the low idle issue, but am unsure of how to verify iac operation other than what I see on the scanner data.
#2 I knew it was the distributor when I followed the procedure using a multi meter, I don't recall what the spec was now but my reading was very low per the procedure I was using from one of the posts on this site. I spun my new dist with a drill on the bench and got a reading in spec.
#3 I hear you on the coil killing icm's
#4 yes it was backfiring into the intake, replaced icm and have not had that issue again.
#5 the delco icm had many metal to metal contact points, not an even
thin coating
#6 I will verify power to coil and icm, just need to get it to stall again for me. Intermittent issues are the worst. I have also been considering the ignition switch,
#7 in my initial post I was going from memory, had the gauge on the fuel supply today and was just north of 10 psig while driving
#8 I do not have a heated oxygen sensor, also not sure what those readings are, I will try to find out on the web.
#9 I just tested the coil with a multi meter reading ohms of resistance. I guess I replaced it with one I believed to be in good working order. I am not good with electrical testing and rely on info from forums like this to fumble my way through it.
#10 yes I meant driver side cylinder head near exhaust manifold.
#11 I agree, just grasping at straws at this point. I pulled the pcv and installed a crankcase breather for the time being to rule it out.

I appreciate the reply. I feel like my initial issues were Tune up relates. This truck sat for a long time before I bought it. It seems like the low idle and stalling were corrected with the distributor and tune up parts, and then this stalling issue started. When it would die when I first got the truck it would re-start by placing it in neutral and cranking. Now it requires the key to be cycled. That seems to be relevant. I guess since I can't get it to stall I may just replace the ignition switch. Thanks again for the reply, all help with this issue is greatly appreciated.

 

[Throwback67]

What does high o2 cross-country suggest?

 

[scott2093]

What does high o2 cross-country suggest?

They really shouldn't be kicking in until the O2 sensor is hot enough . Then it'll start oscillating , "crossing".45v ish up and down....
Your O2 sensor is only 1 wire?

What are O2 counts doing while idling in closed loop?

 

[Throwback67]

LT Fuel TR CL= long term fuel trim closed loop.
I haven't been able to find any reference to the EN. I will keep looking

 

[Throwback67]

When the engine is warm and idling in park the o2 cross-country is around 90. I may have been mistaken about the o2 sensor, just cli.bed under there and it has 3 wires on the harness.

 

[Schurkey]

What does high o2 cross-country suggest?

Cross-counts, not cross-country.

They really shouldn't be kicking in until the O2 sensor is hot enough . Then it'll start oscillating , "crossing".45v ish up and down....
Your O2 sensor is only 1 wire?

What are O2 counts doing while idling in closed loop?

Yeah. I'd expect ZERO cross-counts at 29 seconds of idle-time, as a single-wire O2 sensor maybe hasn't had time to get hot enough to actually function.

I remember my '88 with a somewhat-aged single-wire O2 sensor having 8--10--12 cross counts at fully-warm idle, 20+ as throttle was added.

Your scan tool shows 107 cross-counts at idle with only 29 seconds of idle time. I think that scan tool is lying to you.