New Member here. LT1 don't run need help...

[Ron G]

So I essentially got a 1995 Trans Am for free. The previous owner gave up trying to get it to run like 9 years ago. The body is in very good shape so I am willing to put some time and money into it to get it running.

I was not getting spark so I changed the coil and ignition module and now it does run.. but only if I squirt starter fluid into it. I did not hear the fuel pump running so I pulled that it is was destroyed and the tank was full of all kinds of gunk and debris so I put in a new tank, filter and pump. Pump runs fine and I have good pressure at the rails now.

However, it seems the fuel injectors are not pulsing. I only get a positive reading on both wires and each injector during crank. So I am assuming this is related to something between the PCM and optispark.

Where I stand after todays testing is when taking voltage readings at the 4 wires that go to the optispark from the PCM I have good 12v, good ground, and 5v on each of the resolution wires from the PCM. However when I plug the harness back into the optispark, one of the resolution wires is dropping the 5v out almost down to zero volts.

Does anyone know if this points more towards a bad optical sensor or a bad PCM? Or there any other tests I can conduct to help point me in the right direction or confirm anything? I don't have a spare PCM to plug in and test and I also do not have another known good optispark unit to plug in and test.

I tried to get readings from my old Snap On code reader that has the adapter and chip card to work with that wonky OBD2 port that is actually an OBD1 and it is not throwing any codes nor is any light flashing on the dash. Even the security light goes out like it is supposed to.

Any help would be greatly appreciated as this car deserves to be more then just a giant door stop.

[SSlowBoat]

Vats, sounds like vats to me

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[Ron G]

I don't think its the VATS because that should also cut out crank which is correct for a 1995 Trans Am, and this car cranks and runs on fluid.. and the security light is going out a few seconds after ignition is turned on which is the test that the TDM is sending the correct signals to the BCM and the key pellet is good. I wish this particular problem was that easy as I do aftermarket electronics installations on automotive for a living and the VATS is about the simplist factory security known to man to bypass.

Now there could be a chance the part of the TDM that has to send signal to the PCM to allow the fuel injectors to work is faulty but the part that kills the crank is fine but if that is the case it is supposed to throw a code if the computer is not receiving the fuel enable signal from the TDM. I get no codes.

So.... has crank, sec light goes out, no codes. 3 reasons to kind of eliminate VATS as the cause or at least to look elsewhere.

[Injuneer]

You're in the LT5 section. Maybe @popo8 can move this where it belongs.

Be interesting to see how the responses here compare to the one I just provided on Firebird Nation.

[SSlowBoat]

I don't think its the VATS because that should also cut out crank which is correct for a 1995 Trans Am, and this car cranks and runs on fluid.. and the security light is going out a few seconds after ignition is turned on which is the test that the TDM is sending the correct signals to the BCM and the key pellet is good. I wish this particular problem was that easy as I do aftermarket electronics installations on automotive for a living and the VATS is about the simplist factory security known to man to bypass.

Now there could be a chance the part of the TDM that has to send signal to the PCM to allow the fuel injectors to work is faulty but the part that kills the crank is fine but if that is the case it is supposed to throw a code if the computer is not receiving the fuel enable signal from the TDM. I get no codes.

So.... has crank, sec light goes out, no codes. 3 reasons to kind of eliminate VATS as the cause or at least to look elsewhere.

My experience with vats issues was car would crank and crank but not pulse injectors. I had to bypass tdr relay to make it run. This was a 96 formula



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[Ron G]

That would be kind of strange because the TDR relay is only for crank. I know the wiring for the sec systems in these cars like the back of my hand including the colors there. What kills the fuel injectors is if the TDM is not sending signal to the PCM to enable the injectors and that is supposed to throw a trouble code if failing. If there were just a relay to bypass to get those injectors pulsing again it would have been tried weeks ago lol.

Now there are some other GM vehicles that use a different PK system and some of those will kill fuel but allow crank. Not the gen LT1's I am aware of.

[SSlowBoat]

That would be kind of strange because the TDR relay is only for crank. I know the wiring for the sec systems in these cars like the back of my hand including the colors there. What kills the fuel injectors is if the TDM is not sending signal to the PCM to enable the injectors and that is supposed to throw a trouble code if failing. If there were just a relay to bypass to get those injectors pulsing again it would have been tried weeks ago lol.

Now there are some other GM vehicles that use a different PK system and some of those will kill fuel but allow crank. Not the gen LT1's I am aware of.

I also had an aftermarket alarm in the car and the ignition switch burned up under the dash on the column. Guess I'm wrong.
Good luck

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[Ron G]

I also had an aftermarket alarm in the car and the ignition switch burned up under the dash on the column. Guess I'm wrong.
Good luck

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That makes more sense. If an aftermarket ignition kill relay is messed up it will crank forever but not start if the circuit that was interrupted is for coil or fuel pump/injectors etc. Typically with aftermarket kills we go to the starter crank wire off the ignition switch because there is too much liability if the ignition goes out while driving due to a bad relay or connector or module, but some installers will do ignition kills instead and some systems like the higher end Cliffords did come with both a starter and ignition cutoff circuitry using internal relays.

[popo8]

You're in the LT5 section. Maybe @popo8 can move this where it belongs.

Be interesting to see how the responses here compare to the one I just provided on Firebird Nation.

Moved to GENERAL ENGINE TECH.

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