LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

94 Formula shut down issue.

Old 09-20-2015, 07:53 PM
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94 Formula shut down issue.

I have a 1994 Firebird Formula and last week when I got the car it was cutting out at low throttle after warming up then would clear up under wot. I replaced the coolant temp sensor at the water pump and resolved that issue. Now the car sometimes at wot will backfire and shut down. I can cycle the key and the fuel pump sounds fine. But after the car is warm it takes about 6-8 seconds of spinning it over for it to finally fire. When it is cold it fires right up. After the wot shutdown though, obviously the engine is warmed up but I have to hold the throttle to the floor for it to finally hit and fire. Fuel pressure at idle is around 35psi and when snapping the throttle it jumps to around 45-50 psi then comes back to 35. Again fuel pump sounds normal and it doesnt seem to be leaking down in pressure when the car is sitting and engine is off. Pressure at idle seems to be a little low to me but I am not sure. Then when the car shut down last night after wot run it would spin over hit fire and the pop through the exhaust without touching the throttle, never would fire and run unless it was wot while turning it over. It is also running rich. I am kinda no looking deep into the fuel pump so much as possibly the ignition control module, coil or optispark. Kinda leaning more towards the ignition control module. Really looking to see if anyone has had this issue or if anyone has an idea of what it is. Really dont wanna throw parts at it just to waste money. Car is bone stock by the way.
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Old 09-20-2015, 09:43 PM
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Re: 94 Formula shut down issue.

Does the SES light come on? Have you scanned it for codes? There is at least one code that will shut down the engine that does not turn on the SES light.

35psi at idle is within the normal specification. Remember, the fuel pressure regulator is vacuum compensated, so at idle with high vacuum, the vacuum will reduce the fuel pressure by about 8psi (with a stock cam, less reduction with a more aggressive cam).

Putting the accel pedal on the floor while trying to start it puts the PCM (computer) in "clear flood" mode.

Last edited by Injuneer; 09-20-2015 at 09:48 PM.
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Old 09-20-2015, 09:47 PM
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Re: 94 Formula shut down issue.

Originally Posted by Injuneer View Post
Does the SES light come on? Have you scanned it for codes? There is at least one code that will shut down the engine that does not turn on the SES light.
Check engine is on I havent had time to go get it scanned. My vats has been bypassed before I got it so I thought that the check light could be on for that reason. But then I noticed the security light is on so I doubt it would have anything to do with the check light.
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Old 09-20-2015, 09:48 PM
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Re: 94 Formula shut down issue.

Originally Posted by PopoFormula View Post
Check engine is on I havent had time to go get it scanned. My vats has been bypassed before I got it so I thought that the check light could be on for that reason. But then I noticed the security light is on so I doubt it would have anything to do with the check light.
Also does the fuel pressure sound right to you?
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Old 09-20-2015, 09:57 PM
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Re: 94 Formula shut down issue.

I edited my earlier post to add more info.

Bypassing VATS does not turn on the SES light. The "SECURITY" light being on, and the engine still starting, indicates another component in the PASS-Key 2 system has failed and the system has bypassed itself to allow the engine to start. Could be the TDR (theft deterrent relay) or TDM (theft deterrent module).

Given the problems you listed, best thing you can do is get free download of Scan9495 software, buy a cable, and run the software to produce a data log of key sensors, PCM parameters, and trouble codes. Most auto shops don't have the OBD-1 scanner required by 94/95 LT1's. Get info on Scan9495 in the thread "sticky" at the very top of the "Computer Diagnostics....." forum topic listing.
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Old 10-12-2015, 04:19 PM
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Re: 94 Formula shut down issue.

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