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Old 10-23-2008, 03:46 PM
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96 3.8L GM engine dies seconds after startup

I have a 96 firebird 3.8L sequential fuel injected engine and automatic transmission in a 49 Austin complete with stock engine wiring harness and PCM. I am temporarily using a stock chassis harness for startup of the engine. The engine starts easily and comes to an idle then dies everytime after about 4 seconds. After the engine stops, there are no trouble codes stored in the PCM. All engine sensors check okay, and the fuel pressure at the rail is okay. I suspect some built in security/theft test failure or something like this that is shutting down the injectors, but can not find any details on these control strategies. Any ideas on the most likely cause of the problem or what to test for?

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Old 10-23-2008, 04:17 PM
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Check all of your grounds, and make sure your battery has a ground to the body, if you have the 'computer' grounded to the body.

Also check all the relays to make sure you are not loosing power.

This absolutely sounds like a power, or ground distribution problem. Either one, or both.

The fact of 'no codes' stored verifies this.
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Old 10-23-2008, 04:21 PM
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Quote:
Originally Posted by 49Austin
I suspect some built in security/theft test failure or something like this that is shutting down the injectors, but can not find any details on these control strategies. Any ideas on the most likely cause of the problem or what to test for?
I think you nailed it with the security. Did you have the PCM re-programed? If not you will need to. They should be able to disable the theft deterrent during their re-programing.

Here is a snipit from ALLDATA

"The PASS-Key II system prevents the engine from stating by controlling the theft deterrent relay and the PCM fuel enable input. If the PCM does not sense the proper frequency signal on the fuel enable input, it will not provide fuel to the engine."


Steve
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Old 10-23-2008, 05:06 PM
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Quote:
Originally Posted by 1931 steve
I think you nailed it with the security. Did you have the PCM re-programed? If not you will need to. They should be able to disable the theft deterrent during their re-programing.

Here is a snipit from ALLDATA

"The PASS-Key II system prevents the engine from stating by controlling the theft deterrent relay and the PCM fuel enable input. If the PCM does not sense the proper frequency signal on the fuel enable input, it will not provide fuel to the engine."


Steve
Steve. This was my first thought. I assumed the 'security' had been bypassed. The fact that it actually starts and runs for a few seconds, sort of supports my thoughts.

In this case anything is probable, or possible given there is no information about the ignition, or steering column used.
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Old 10-24-2008, 01:23 AM
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Thanks for all the suggestions. I will double-check that the ground leads from the PCM have been properly grounded. The engine, chassis and battery are grounded, but I will check this as well.

The steering column/ignition is from Ididit and wired according to their wiring diagram. A by-pass wire has been added around the theft deterrent relay on the fuel pump circuit so that the fuel pump receives power during startup and run. The fuel rail pressure before and after the engine stops stays within specs.

Steve, I have not had the PCM reprogrammed (didn't know this could be done) and had hoped that simply bypassing the fuel relay would work. The information from Alldata is helpful as I don't have access to this.

Would the PCM also shut-down the injectors or ignition in addition to controlling the power to the fuel pump circuit if it didn't sense the proper frequency signal?
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Old 11-23-2008, 09:54 PM
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Solved the stalling problem using a vehicle anti-theft system bypass circuit from Baker Electronix which sends the key-okay signal to pin 55 on the blue PCM connector.
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Old 11-27-2008, 12:40 PM
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I chased my tail on that one before... Dang that's frustrating!

Also had the similar problem on a 99 Blazer. I had to turn the key on for 10min at a time till the "securty" light flashed.. turn key off... back on for 10min.. off for 30min. Great fun. But after that it re-programmed it and fired/ran fine.
Glad you found it!~
Scott
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