Fuel Pump Prime Circuit

Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic

   OK so I know that the fuel pump will fire with oil pressure, and my issue is, that the fuel pump prime is not working, and until I have spun the motor enough to build oil pressure the pump won't fire.  So where do I look.
I assume that the fuel pump relay must be working if the pump runs, as I don't think the oil pressure circuit has enough voltage to run the pump, or better stated, can carry enough amperage to run the pump.
Can anyone offer any suggestions as where to look.
This is on my 88GT that we just put the motor into.   Yesterday I gasp took it into a shop as I was too tired and hot (in the upper 90's) to work on the car, thankfully the shop that I took it to is a close friend and fellow Fiero owner so I knew the car was in good hands. I needed to get the E-Brake adjusted, and just didn't want to be on the ground doing it, and I knew they had an alignment rack the car could just be driven onto with easy access to the cables.  Once that was fixed,  he noticed the fuel filter looked old, so we pulled it and on inspection found it to be very nearly plugged.  Extremely hard to blow through.  So the pump must have been working really hard.   
Suggestions anyone?

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
Capt Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Founding Member Joined: 12 February 2007 Location: Canada Status: Offline Points: 4039	Post Options Post Reply Quote Capt Fiero Report Post Quote Reply Topic: Fuel Pump Prime Circuit Posted: 18 August 2012 at 10:09am
	OK so I know that the fuel pump will fire with oil pressure, and my issue is, that the fuel pump prime is not working, and until I have spun the motor enough to build oil pressure the pump won't fire. So where do I look. I assume that the fuel pump relay must be working if the pump runs, as I don't think the oil pressure circuit has enough voltage to run the pump, or better stated, can carry enough amperage to run the pump. Can anyone offer any suggestions as where to look. This is on my 88GT that we just put the motor into. Yesterday I gasp took it into a shop as I was too tired and hot (in the upper 90's) to work on the car, thankfully the shop that I took it to is a close friend and fellow Fiero owner so I knew the car was in good hands. I needed to get the E-Brake adjusted, and just didn't want to be on the ground doing it, and I knew they had an alignment rack the car could just be driven onto with easy access to the cables. Once that was fixed, he noticed the fuel filter looked old, so we pulled it and on inspection found it to be very nearly plugged. Extremely hard to blow through. So the pump must have been working really hard. Suggestions anyone?
	Capt Fiero 88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd.

Dawg Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 15 August 2009 Location: Canada Status: Offline Points: 988	Post Options Post Reply Quote Dawg Report Post Quote Reply Posted: 18 August 2012 at 10:00pm
	Been a while since I looked at that diagram but you should confirm that applying power to the ECM feed to the pump relay actually makes the pump run. Then you know the wiring is fine up to the ECM. If I remember right, there are pins in the OBD plug that allow you to run the pump manually. Try that maybe. It's either a bad connection (likely), or your computer is flakey. I like the first one better. How about you? Dawg
	You dream it up....I'll make it

CFoss Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 February 2007 Location: Canada Status: Offline Points: 580	Post Options Post Reply Quote CFoss Report Post Quote Reply Posted: 19 August 2012 at 11:57pm
	Here's a snap of the circuit. It's an '86 but i doubt it changed: Looks like the oil pressure switch is a seperate parallel path to the pump. In other words, the oil pump sweitch can handle the load (amperage) of the pump just fine, however this is a backup mode as I'm sure you know. The ecm picks up the relay with a +12 signal. The ecm should prime before crank, and hold the relay in as long as it's receiveing ignition pulses from the distributor. If it's not doing the prime and/or running at crank, I'd suggest looking for +12 pulse at 'A' on the relay and go from there. If it's not there, it comes from pin 'A1' on the ecm, you can try to find it there. If the engine is running ok the ecm is probably fine and it's the relay or some connection around it. BTW I know what you mean about the heat...I've been hauling engines out of my boat for the last 2 days...holly crap I needed a siesta today!! Chay
	86 SE 3.4

Capt Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Founding Member Joined: 12 February 2007 Location: Canada Status: Offline Points: 4039	Post Options Post Reply Quote Capt Fiero Report Post Quote Reply Posted: 20 August 2012 at 12:09pm
	Thank You both for the input. I drove the car around a fair bit yesterday while picking up my new project Fiero. I have not yet bought a new relay, but I am really starting to think that the relay is the problem. The Prime started working, then sometimes the pump sounded flaky, like it was intermittent voltage. Then other times nothing at all would happen. Once it was running it was always fine. Dawg, yes if I apply voltage via the OBD wires the pump fires up and runs just fine. I have spare used relays here, but being as new relays are all of 15 bucks, I think I am going to buy a new one and see if that fixes it. If it does not fix it, at least I will have piece of mind knowing that I have a new one in their.
	Capt Fiero 88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd.