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350 Tbi No Start No Injector Pulse


1snake
09-02-2004, 06:13 PM
Here is a tough one for you. I rebuilt a stock 350 TBI for a local feedyard. This truck came into my shop blown to smitherines, so I cannot attest to how it ran before.

The rebuild was your standard first class job, but I did reuse the stock accessories like the TBI unit with exception to the distributor. I was going to use it, but the original was so crusted with crap inside the housing, that I ended up using one that I had laying around the shop. I installed a new pickup coil in it as they are responsible for alot of problems with these engines.

I put the engine in, and ran it around town for a couple of days, had no problems, so I delivered the truck to the feed yard and called it good.

The owner called me a couple of days later and said that it had died a couple of times and said it would restart sometimes and sometimes not.

I proceeded to the feedyard, and checked the spark (none) and the injector pulse (none). I replaced the ignition module, and it fired right up, problem solved! Wrong!

The same thing continued, so I went ahead and replaced the magnetic pickup and distributor shaft itself, making every item in the distributor new. I drove the truck for 3 days with no dying or no start problems, returned the truck, only to be called telling me it's still doing the same thing.

Now, I have observed that once the truck reaches operating temperature, and is shut down and allowed to heat soak for 10 minutes or so, it will lose it's injector pulse and spark and fail to restart.

This makes me think I either have a NEW faulty pickup coil or somehow the ECM is bad, but since the ECM resides in the glove box, it really isn't subjected to underhood hot soak conditions, so I believe the culprit is still in the distributor. I don't think the coil will cause no injector pulse situation, so I have ruled that out lightly, I did try another coil once when it wouldn't start and it failed to start with a known good coil.

Whadya think?

I have thought maybe a ground problem, but I fail to see the temperature fluctuations causing bad grounds to flare up, I had thought maybe just bad wiring connector connections too, but the temp fluctuations makes me think it's actually an electronic component of some kind.

95silverado
09-02-2004, 08:04 PM
Have you used freeze spray on the electronic componets? We use it in the electronics industry to isolate heat related problems.

rpreston
09-03-2004, 11:50 AM
You didn't mention what year it is, but doesn't the ECM monitor a output signal from the oil pressure sending unit behind the distributor when the engine initially turns over? I don't remember what years it referred to, but I'd read an earlier post about the ECM shuting off the distributor and injectors if it doesn't see the signal during startup. If that's the case, maybe yours has a heat problem. Maybe someone else will post on this who knows for sure.
Rick

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