Urgent 94 Pontiac Firebird Trans am starts and stalls - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
 
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post #1 of 13 (permalink) Old 07-31-2018, 08:04 PM Thread Starter
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94 Pontiac Firebird Trans am starts and stalls SOLVED

Alright, So about a week ago I had picked up a 1994 Pontiac Firebird Trans am 5.7L v8.
After getting it home and charging the battery, tried to start it up it would just stall out after 2-3 seconds.
It was basically like someone was turning the key off.
Even when I tried giving it gas.

I changed the optispark, plugs, wires, MAFS, water pump, fuel filter.
I even ordered a new computer programmed to the cars VIN because someone had tolled me the computer wasn't for that car.
(The fuel pump was brand new already)

After putting it all back together it still does the same thing it did before, starts and stalls out after 2-3 seconds.

Fuel pressure and everything else seems to be good.

Also.. I do not believe it is the security system, because the security light goes out after 5 seconds.

Any help is appreciated, I am currently out of ideas.

Last edited by JacksonHogan01; 08-02-2018 at 10:37 PM.
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post #2 of 13 (permalink) Old 07-31-2018, 08:56 PM
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Have you put car on an obd1 scanner and checked for codes. Dtc 16 & 36 for opti problems & 41 & 42 which are icm problems, don't light the cel. When you checked fuel pressure, did you actually put a fuel pressure gauge on fuel rail?


Pressure should be around 43 psi @ key on prime. And mid 30's when idling. A faulty map sensor or lack of vacuum to map sensor can cause engine to stall. As well as ignition problems & fuel pressure problems.


Plus theft deterrent module (TDM) which sends 50 hertz fuel enable signal to pcm can partially fail. If fuel enable signal is not proper square wave, car will die after 2 or 3 seconds of running. Only way to check fuel enable signal is with an oscilloscope. People suggest using a multimeter to test fuel enable signal. This tool only indicates if voltage is present and not if proper square wave is being sent to pcm.


And don't assume that a newly replaced part is good. Many new parts are bad right out of the box. Last but not least, here's a link to the 94 service manual. It will have wiring diagrams, driveability & emissions section with trouble shooting. My Files
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post #3 of 13 (permalink) Old 07-31-2018, 09:14 PM Thread Starter
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Quote:
Originally Posted by cocobolo95 View Post
Have you put car on an obd1 scanner and checked for codes. Dtc 16 & 36 for opti problems & 41 & 42 which are icm problems, don't light the cel. When you checked fuel pressure, did you actually put a fuel pressure gauge on fuel rail?


Pressure should be around 43 psi @ key on prime. And mid 30's when idling. A faulty map sensor or lack of vacuum to map sensor can cause engine to stall. As well as ignition problems & fuel pressure problems.


Plus theft deterrent module (TDM) which sends 50 hertz fuel enable signal to pcm can partially fail. If fuel enable signal is not proper square wave, car will die after 2 or 3 seconds of running. Only way to check fuel enable signal is with an oscilloscope. People suggest using a multimeter to test fuel enable signal. This tool only indicates if voltage is present and not if proper square wave is being sent to pcm.


And don't assume that a newly replaced part is good. Many new parts are bad right out of the box. Last but not least, here's a link to the 94 service manual. It will have wiring diagrams, driveability & emissions section with trouble shooting. My Files
I will have to check the map sensor, but the fuel pressure is around 40 psi primed, and drops to 35 psi when it does run for the 2 seconds.
I do know it is nothing with the fuel pressure or getting fuel, I manually pressurized 35 psi of fuel into it.
I will check the map sensor in the morning and get back with you, much appreciated.
Feel free to post if you have any other ideas for me.
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post #4 of 13 (permalink) Old 08-01-2018, 09:37 AM Thread Starter
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After checking the map sensor, its getting the proper voltage and seems to be working just fine.
Also... I'm supposed to have a service engine light? correct? Because There is no check engine or service engine light popping up.
But the check gauges light is always on.
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post #5 of 13 (permalink) Old 08-01-2018, 09:44 AM
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Does your check engine light come on when you turn key on, then go out after a few seconds?


Your check gauges light comes on when a gauge reading is far out of expected readings. Are any of your gauge reading way off?
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post #6 of 13 (permalink) Old 08-01-2018, 10:03 AM Thread Starter
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No gauges are reading off that I can see, but the check engine light doesnt come at all, like never.
The check gages light goes off when it does start for the 2 seconds.
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post #7 of 13 (permalink) Old 08-01-2018, 10:24 AM
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You need to get the 94 service manual at the following link. Then check out you check engine light circuit. Last owner could have removed bulb to mask a problem. Or bulb could be burnt out.


If neither of those 2 reasons for no cel, check the wiring for the circuit. It will be in both wiring diagram section & driveability & emissions section.
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post #8 of 13 (permalink) Old 08-01-2018, 11:32 AM Thread Starter
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Alright, so the owner before me had taken the lightbulb out for the service engine soon. I put the light bulb in it. The light just stays on, it doesn't give any codes.
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post #9 of 13 (permalink) Old 08-01-2018, 11:59 AM Thread Starter
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Is it possible it's the oil pressure switch? The oil reading on the dashboard is reading good, but could the other oil pressure switch be bad?
If so, where is the oil pressure switch for the computer?
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post #10 of 13 (permalink) Old 08-01-2018, 12:31 PM
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I forgot to put the link in for the 94 service manual My Files


When you say you get no codes did you use the old short the 2 cavities of aldl together? If you did, that only works on 93 & older models.


To read codes on your 94, you must use an obd1 scanner. And not one of the cheapies that are sold. All they do is short the cavities together for 93 & older carDon't think you have an oil pressure sender problem. However since there are 2 coolant sensors, you may have a problem there.


If coolant sensor on water pump, which gives pcm info, doesn't agree with gauge reading provided by 2nd coolant sensor, check gauges light could come on.


Her's a link to a site with component views section. It will tell you where things are located. Lots of other good lt1 info too. shbox.com


Also in service manual, near the end of the wiring section, will be a component views section. Starting on page 8A-201-0.
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post #11 of 13 (permalink) Old 08-01-2018, 01:40 PM Thread Starter
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I have someone coming out with a scanner tomorrow, I had one of the cheap scanners that would just short it, so no wonder I wasn't getting any codes. I do not have any collant in the car yet, because I was flushing it. But it still should still stay running for more than two seconds without collant.

Also, I thought from what I read is that if the computer reads less than 4psi of oil pressure it will kill the injectors or something?
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post #12 of 13 (permalink) Old 08-01-2018, 05:17 PM Thread Starter
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I'm not sure what else to do, Everything seems to be working fine. Good oil pressure, good fuel pressure, has spark... sensors seem to be working good.
Anyone got any other ideas?
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post #13 of 13 (permalink) Old 08-01-2018, 08:45 PM Thread Starter
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Update: Just replaced the ignition coil because it had cracked and looked pretty wore out... That didn't fix it.
I've replaced just about everything I can, it's got to be something stupid.
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post #14 of 13 (permalink) Old 08-02-2018, 12:56 PM Thread Starter
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Update: The problem has been fixed. There is a dark blue wire that hooks up from the theft deterrent module to the computer, I had to cut that wire and while trying to start the car someone was tapping the wire to a ground... It started right up and ran perfect.
Therefore the problem is going to be the theft deterrent module being bad most likely. But I can simply just hookup that wire to a button that I have to press a couple times while starting.

I appreciate everyone's help!
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