Stalling w/ no forewarning - 2500HD

This morning on the way to work my truck stalled twice, unexpectedly, while sitting at a traffic light. The engine had warmed up to normal operating temperature and was running like normal before it stalled, and would run fine after restarting it.

The truck is a '98 Chevy w/ the 5.7L, automatic transmission. Any thoughts would be appreciated.

Thanks,
Webb

Maybe a little water in the gas?

My '02 did that a couple of times a few months ago. I removed the idle air control motor and cleaned it and cleaned the throttle body and the problem hasn't returned.

If there is water in the fuel, I assume the whole tank would have to be drained? Or could I simply replace the fuel filter several times over the course of a month or so? Does the fuel filter filter water, or just debris?

What are the symptoms of water in the fuel? Woudn't the engine also run rough? I am suspicious of the seal around the tank where the fuel pump is mounted. I am also suspicious of the fuel pump itself.

Just trying to determine if it's water in the fuel, a fuel pump starting to go bad, or maybe the electrical connection between the wiring harness and the fuel pump?

There has been a lot of rain lately, so that would reinforce the water in fuel idea.....

A weak fuel pump will usually show up as a longer cranking time before starting or loss of power at w.o.t./going up a big hill, pulling a trailer, etc. If the seal on the tank is bad, it'll usually cause a trouble code (can't remember the name of the system off hand) but no driveability problems.

Try 2 cans of Heet or other gas line alcohol.

I will try the HEET, thanks for the suggestion.

Does anyone know if any of the auto parts stores will hookup a scanner for free to check for codes? I am not interested in taking the truck to a dealer and having them charge a lot of money for a scan.

Thanks.

Auto Zone but there are others.

the oreilly's near me will scan for free too

Auto Zone did a free scan and there were no codes in the computer. I also bought two bottles of HEET and put those in. I did not have any other troubles today, so we'll see what happens. Hopefully it was just a little water. Thanks for all who replied.

Still having troubles today. The problem seems to be electrical. Everytime it happens, the truck is running great, completely normal, then it dies all of a sudden. No coughing or running rough, just a smooth shut down. Sometimes it starts up right away, and sometimes it has to crank for a while, I even had to crank it 3 or 4 times on one occurance.

Whenever it starts again, the truck runs completely normal, until it suddenly dies again. Everytime it dies I have been sitting at a stop light or stop sign.

I've checked the battery terminals and all exposed electrical connectors around the intake are tight and intact. I wiggled some of the hoses and wiring harness leading to the fuel pump and that changed the tune of the humming fuel pump slightly, but I couldn't get it to shut off.

Any more ideas?

If you truck has a distributor (not separate coil packs), you may want to try new cap and rotor, the later 90s 5.7s had a real problem collecting moisture in the dist. caps and rotting out the contacts. Usually that causes a bit of a miss when it's running though and harder starting, espcially if the air is moist.

I will definitely check the distributor cap, but the enitre distributor was replaced last year (including cap and rotor), so I don't think that is the trouble, but I won't rule it out until I check it.

How quickly and smoothly would the truck shut down if the fuel pump lost power? I guess that I could just let it run and pull the relay to see how quickly and smoothly it dies.

I'm leaning towards pulling the bed off and checking / installing a new wiring harness leading to the fuel pump. And after that I would maybe replace the fuel pump, but just trying to steer away from buying a new GM pump because they are so expensive.

If you can get access to a fuel pressure gauge, check that before you do too much with the pump. Usually you can rig them up so you can watch them as you're driving and notice if the pressure drops significantly when it stalls.(If nothing else, I once removed a hood and wired the guage up so it was visible through the windshield) You do need a high pressure gauge, as these systems run around 60 psi.

My 97 stalled the other day then soon restarted but soon stalled again.
Been through three fuel pumps in 5 years and last time I cut an access panel in the bed for easier replacement of the pump. I carry a pressure gauge in the truck. I also have the scan tool in the truck.
This time I found the relay was sensitive to vibration, and when I gently tapped it, the pump quit. So I replaced the relay and no more trouble.
Previously the relay had no effect on the failures.
Bob B

After a thorough cleaning of the throttle body, idle air control valve, and mass air flow sensor, the stalling problem has not returned. Although I'm not 100% convinced that it's fixed yet, the idle air control valve had a lot of cabon build up on it, and I think that was the problem. Either way, I'm remaining hopefully after no troubles for the last few days.

I had also jiggled the fuel pump relay around for a while, maybe that cleaned the contacts just enough to make it work. We'll see what happens next.