I am about finished putting a '95 LT1 out of a Trans Am into an '86 Firebird and I cannot get the fuel pump relay to fire. I have the green/white hooked to the signal, power coming from a switched source, ground and output hooked up right but still won't fire. I can jump the relay from a 12v source and it will click the relay and fire it. I measured the voltage coming from the signal wire and it is around 9.7 volts. I contacted someone who measured the voltage from a car that I actually plugged my PCM in to program the vats and egr out of it and it would start the car and let it run and he measured 10.1 coming from the signal wire to the relay. This really has me stumped, the only thing I do not have is the C100 plug out of the PCM hooked up which has the power to the injectors and ignition, is it possible that this is causing the problem? I have tried 3 different relays, the original that came off of the 86, a universal 12v 4 pole relay, and a direct replacement for a 95 Trans Am.

Thanks for any help

 

Nobody has any ideas?

 

The fuel pump output on the PCM only primes the pump when you turn the key on. After that, the oil pressure sender keeps the relay grounded. I did the same thing when I did a built LT1 and 6 speed in a 92 RS. About pulled my hair out on that one. So, you need the PCM output to go to the relay and also the wire from the oil pressure sender that is the same color; the sender will keep the fuel pump going as long as the engine is running. That way, if you get in an accident or the engine dies, the pump will quit pumping.

 

Now I have done away with the original ECM on the car and the wiring using strictly the LT1 harness and PCM, the relay will not even close to prime the pump.

 

Make sure that the wire from the PCM is going to either 85 or 86. Then, make sure the other terminal (85 or 86) goes to power, not ground. Then, make sure you have power on 87 and make sure the pump wire goes to 30.

Ryan

 

Hmm...that's backwards to what every wiring diagram has showed me. I have power going to 30, Signal going to 85 ground going to 86 and fuel pump wire going to 87, that's what the Mitchells has in the book, I'll try that and see what happens.

 

Well, tried to connect it up and still no relay close and no signal to the fuel pump. Anyone else know of anything that could cause this?

 

Your 87 and 30 are fine. HOwever, 85 and 86 are the terminals for the coil that energizes the relay. The PCM puts out ground so the other terminal needs +12 volts. IF you have all of that right and it won't fire the relay, the relay is bad. If the relay is good, it's not wired the way I said it should be. A quick test you can do: put a jumper between 87 and 30. Fuel pump should run. If it does, let me know.

Ryan