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91' Dying during start cycle

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85CUCV

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We've got a 1991 Chevy 1.5 ton with a fuel injected 454 that keeps dying during the start cycle. Sometimes it does not die. Other times it will die 6 times before it warms up. Once it warms up it runs fine. We cannot fine the problem. Local mechanic can't find the problem. Any suggestions?

Thanks
 
"Dying" is kind of vague. Need more info.

Starter stops turning, engine starts but stalls, etc.
 
Engine starts, runs, dies. Might run fine for 30-60 sec and then die. From my understanding there is a start cycle in the computer? This all happens in the first 5 minutes off running. After that it runs fine. It does not flutter like a choke issue when it does die. It just stops running and and starts right back up when you crank it over. Occasionally it starts and runs fine.

Thanks
 
Does it have a high idle when first starting up, which then lowers back down when the engine warms up? Should be pretty noticable, but if it's not doing this then something isn't quite right. Maybe the IAC is not working, or even the temp sensor is feeding it the wrong information and it's not thinking the engine is cold.

I don't know exactly how this particuliar truck is setup, but in general these are issues I have seen in the past. The above is basically the same if you were trying to start a carb'd engine without a choke on it.
 
Has anyone ran a diagnostic scan? Checked for any trouble codes?
Coold be a bad coolant temp sensor, Vaccum leaks, Dirty IAC valve, dirty /stuck EGR valve.
 
6.2Blazer- it does have high idle when you first start it.

Thunder- I assume when dad took it to the shop it was scanned. The mechanic used to work for GM. Cannot say 100%. I'll check today.

Thanks for the help guys, I'll run over to the farm next week and look at it some more. My dad has been fighting this issue for awhile and has been unable to diagnose the problem.

Thanks again
 
chevyuser74 said:
i wouldnt rule the computer out either
Click to expand...

Don't rule ANYTHING out, however the ECM should always be your LAST resort at replacing. You should have already *tested* everything and verified that it all works before blaming the ECM. Even a bad connection can make you believe it's a "bad" ECM. Simply unseating and reseating connectors can solve intermittents, but that's why a good visual is important. BTDT, even the manual said it was a bad component when in fact it was one bad wire connection.

Don't buy into someones opinion because they should know what they are doing (talking about mechanics, not people here). Most anymore are nothing but parts changers, any service manual made nowadays will prove it. Not saying there aren't good ones of course, but the majority you see and hear about take shortcuts (like replacing parts instead of diagnosing a problem), almost always at your expense as a customer.
 
im telling the guy to replace it, all i said was i wouldnt rule it out, i know we can test them at work, but if he had one laying around, it doesnt take but a couple minutes to swap em.
 
Right, if you've got known good, it doesn't hurt to try and swap. At the cost of the ECM, not worth replacing just because though.

Problem with a lot of bench testing is that electronics can get weird when they warm up, or get jostled around like in the truck.
 
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