monteash

350 TBI starts and runs great for about 20 minutes. At 20-30 minutes just shuts off. After that, no spark but good fuel at the injectors. If the truck sits for a few hours itwill start and run for 20-30 minutes and die again. New cap, wires, plugs and coil. Checked pick-up coil, reads 700-800 ohms. Ignition module passes test when hot at AutoZone. Did the full troubleshooting routine out of Haynes manual, all good.

No stored codes when this happens.

So now that everything that it could be is eliminated, what else would cause the engine to die after 20-30 minutes every time?

Thanks for help and advice.

Monte

triplereef

This is an old thread -- hoping someone else finds it. i have a 1990 c1500 4.3l v6 - tbi -- Problem began as exact same symptoms as the original post. truck will start up and run great until it warms up - or about 15-20 minutes in idle. after which it dies and it will not start unless I let it sit for a couple hours; then, same thing starts up fine, runs great then dies. no misfiring/backfiring/rough starting . . . all is good when it's good. There is no spark when it isn't starting - no fuel coming through the injectors. fuel pump is whirring -- i replaced the fuel filter. i went through the t/s steps in haynes manual for the entire ignition system -- all tested ok -- I took the ignition module to autozone, it tested ok as well. I replaced the pick-up coil out of desperation - took out cleaned relubed the distributor (had to to get to the pick-up coil) after which still same symptoms - starts up runs for a bit then dies. ignition coil resistance checks are ok - all wires look ok - resistance on ign. coil wire was appropriate -- just no spark at plug, or from ign. post - 12+ volts getting to the module and the coil. there is no ckp on this year truck. any thoughts?

fredrich03

A friend of mine had this prob. with a 94 350. We replaced the complete distributor with a new one from napa and it runs great.
Good luck!

triplereef

I might end up resorting to that -- when I took out the distributor shaft the star-shaped magnet (not sure what it's called) was a bit rusted - I sanded it back just to metal and the rotor seemed to spin better, but was thinking it'll need to be replaced eventually.

I'm wondering -- I went through the primary and secondary resistance checks on the ignition coil -- and they were fine, but can it still be bad even if those basic checks come back ok?

Also I failed to mention that when the truck will not start the SES light and the "check gauges" light comes on. When I check the codes there's only code 12 - nothing else.

RacerX

I m thinking it is the ignition control module. High resistance when hot giving you no spark. Works in the limits on the bench, but on the bench it is never hot. You have to take it out of the car then go down to AutoZone or wherever to test it. That timeframe where is loses heat may be where you cant detect if its good or bad.

Code is System OK, but there should be a code or two after that

triplereef

I was hoping for a code after 12 also - but none came, keeps flashing 12. I through my anger at the computer first, but then remebered that it bypasses the computer untill after it's running. It's looking like step by step replacments, since everything is testing ok -- luckily there not expensive, but will have to be a cliff hanger till after the new year.

RacerX

it doesnt bypass the computer. It wont run without the computer. dont do the shotgun approach, wastes money. Replace the igntion control module and see what happens.

triplereef

Finally got some cash to make the repairs. I replaced the primary ignition coil. No change. I took the ignition control module out and replaced it - FIXED!!! That's the module that I had autozone check on their machine that tested ok. I got the new module at advance for 48 bucks (B+D). It started right up and is continuing to run now after warming up.

Thank yall again for all the suggestions.

RacerX

Sucker was expensive right?