BiggTrav

workin on a 92 firebird 5.0tpi wit a 5 speed. i can bypass the fuel pump relay and wit a jump wire it starts fine but. if i put a relay in it it wont start at all unless u crank it real long and that only works if its been started within a hour. any longer than that and it wont. weve replaced the computer and oil press sw. fuel press reg. and the injectors. and nothing has fixed it.im lost and have no idea what else it could be so anyone have any ideas let me know

thunderstick

i might be missing the boat here, but when you do get it started, or attempt to start it, have you done a fuel pressure test? with having to crank for a long time, may be an indication. if you jump it st the test terminal, does the pump run and will it start? with the relay installed.

thunderstick

also, did you change the filter?

BiggTrav

ya changed the filter and once its started the car runs fine the only problem is starting. it wont start with the relay in it we took the relay out and ran a jumper wire batt side of plug to fp side and it starts

86White_T/A305

Just lil suggestion that I had to deal with in this area aswell.Since I do enjoy having a clean engine bay and wash her down... moisture and corrision on wire terminals.. especially relay sockets make for some great intermittent electrical problems.Use a test light or multimeter and double check you are getting power at the proper wires etc and clean up the contacts and then try a new relay.I had to cut off the factory relay and then soldered in water proof relay and harness on alot of things and chased out lil problems such as these.Once you know that your no longer dealing with the actual wiring of your fuel problems start looking elsewhere such as fuel pressure as mentioned..bad injectors..or bad diaphram in the regulator like mine was after scratching my head why i was always turning up the fuel pressure and not being able to hold pressure in the rails.Good luck and keep us posted.

86White_T/A305

And another note, dont be shocked if hard to start or long crank issues arent fuel pump related and being old dont supply enough for during crank.Mine also buggered off on me during my fuel issues.Was a very fun week lol! With a dying pump I had to cycle turing the key on and off to build enough pressure to start the car without cranking for 10 seconds.Then i finally replaced it with a 255lph pump and now its half a second or a second to start depending on how cold the motor is.Now that I chased my problems i can buidl from that and put my afpr on and see what effects bumping up to 50psi will do with my 24# injectors.

ZZ28ZZ

There's 2 ways to power the fuel pump:
1. ECM senses eng rotation and activates the fuel pump relay, which powers the fuel pump. Also when key is turned to the "run" position, the ecm activates the fuel pump relay for a few seconds then shuts it off. If it's quiet and everything is working right, you should be able to hear the fuel pump kick on for a few seconds.

2. When oil press is built up, the oil press switch will also send power to fuel pump.

#2 is why the eng will start after a long cranking time cause you've built up enough oil press to turn on switch.

You most likely have a bad connection or broken wire between the fuel pump relay and the ecm.

I don't remember (or have a schematic handy) if the ecm provides power to the relay or if the ecm provides a ground for the relay.

Do you have 12v on the small wires for the fuel pump relay?

BiggTrav

i checked the plug out and the prongs were bent on the inside so i straightned them out and put a new relay on it and it starts every time. thanks for the advice

86White_T/A305

Gotta love this site for quick fixes for our cars