1992 K1500 Suburban intermittent stalling

[dwntwn]

1992 K1500, 268,000 miles, 5.7 liter

This only happens after its been started and brought up to operating temperature, then shut off and been sitting for at least 40 minutes.
When the truck does the stalling bit, it will start and run for about 5 seconds, then die. Starts, runs for a few seconds, dies.

It seems to be heat related—if its parked in the sun it will do it, if I park it in the shade, give it some time, it seems to start and idle normally.

Fuel pressure is 10.5 pounds, I replaced the filter when I did the pressure check.

No engine codes, I took it to my friend's shop, he has a nice scanner and while it was running we checked everything out. No codes, everything seemed to be ok. I replaced the thermostat (195), the coolant temp sender, found a couple of small vacuum leaks, but nothing seemed to be the culprit.

One time it did it while i had a friend with me, I pulled the air cleaner and looked down the throttle boy while it did this. I had assumed it wasn't getting fuel when it does the stalling—it acts like its out of fuel but the injectors are spraying fuel when its running really rough.

The ignition coil, distributor and module are of unknown age, so I did the coil first, no change. Then I pulled the distributor and it was original, really worn out, kind of hard to turn.

I replaced it with a brand new one, new cap and rotor, new ignition module. The plugs and wires are from last summer.

Not sure what direction to go next.

[ChevyTech]

It sounds like heat could be causing the ignition module in the distributor to break down.

Many auto parts stores in my area will test the distributor module for free if you bring it in.

The test results from these stores are not always accurate, and some times the will say the module is good when it is not, but for a free test that may find the problem it is worth a try.

Did you put heat sink compound under the module when you installed it? The compound helps dissipate heat from the module. Without it, the module will fail.

Many people are reporting that the new distributor modules they have recently installed are failing. The quality of replacement parts is terrible.

[dwntwn]

Thanks for the reply ChevyTech,

I can remove the module and get it tested

I bought the entire distributor assembly this morning, the module, rotor and cap were already put together—I can find out when I take it out if they used heat sink compound

[dwntwn]

Update:
The modules are both good (the old one i took off, and the new one) so I was back to square one.

Since I could get the truck to do the stalling symptom pretty regularly in my yard after 40 minutes of being shut off after being brought to operating temperature, I decided to check the fuel pressure again—to see if I could get it to stall and look at what the pressure while that was happens.

(I've been told the spec is 9-13 pounds)

The truck reads 10 pounds all the time but will drop to 9lbs, and when it's at 9 the idle will stumble a bit, but since I've had the gauge on we've had a string of chilly days (for Tucson anyway) and I haven't been able to get the truck to stall and confirm the pressure drops below 9 lbs.

I'm suspecting the fuel pump, now but really want to have it stall and see that its below spec when it does it.

[ChevyTech]

I sure thought you would find a bad distributor module.

The fuel pressure spec is 9 to 13 pounds but anytime you see a TBI running near the bottom end of the spec start considering a upcoming failure or a problem beginning to take place.

With everything in good condition these trucks have pressure in the upper half of the range. Judge this only after you have used the fuel gauge on several vehicles to know where it usually reads.

If you think it could have something to do with the ECM getting hot you could warm it up with a hair dryer and see if the problem shows up but don't get carried away and get the ECM HOT.

[dwntwn]

Agreed on the module...I was thinking of just buying an AC Delco one and trying it but its not my vehicle, not my money to spend.

The fuel pressure test was free, so i figured why not?

Anyway, its below 9 when it starts now, and it will stall. It takes about 5 times to get it to start, I'm wondering if the pump builds enough pressure/volume with the repeated starts?

Either way, the heat angle is what is really making me not 100% certain the fuel pump replacement will actually solve this.

The ECM is under the driver seat, right?

Thanks for the replies, CT!

[Rod_Lei]

The ecm is under the glove compartment as far as I'm aware. If the pressure is low throw a fuel filter at it, but it will usually be the pump that is bad. These TBI trucks are very sensitive to low fuel pressure and will usually only set a code after a year of terrible performance. If low pressure condition is confirmed, change the pump with a Delco Black label pump and be surprised at the sudden steady idle.

[ChevyTech]

As Rod_Lei stated the ECM is behind the glove box. The full size vans, G-vans had the ECM under the seat.

If the fuel pressure is low take care of that. Hard starting is a symptom of low fuel pressure. When the pressure is low, cycling the key to get it to prime the pump a couple times without cranking the engine may help it start on the first try.

Here is a thread with good fuel testing discussion:
http://67-72chevytrucks.com/vboard/s...d.php?t=375132

[dwntwn]

We replaced the fuel pump and it seems to have stopped.

The last morning I drove it, before the fuel pump replacement the truck stalled first thing in the morning (no heat involved) it started on the second try.

The day before I was driving it in the heat and it didn't want to start until I cycled it a few times, so that helped.

Thanks for the replies, Rod and CT!

[ChevyTech]

You're welcome, and thank you for the update.