Fuel Pump Prime Circuit
Printed From: West Coast Fieros
Category: Technical Topics Forum
Forum Name: Technical Questions and Discussions
Forum Description: Got a technical question about your fiero? ask it here.
URL: http://www.westcoastfieros.com/forum/forum_posts.asp?TID=3026
Printed Date: 22 November 2024 at 3:55pm
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Topic: Fuel Pump Prime Circuit
Posted By: Capt Fiero
Subject: Fuel Pump Prime Circuit
Date Posted: 18 August 2012 at 10:09am
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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. |
Replies:
Posted By: Dawg
Date Posted: 18 August 2012 at 10:00pm
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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 |
Posted By: CFoss
Date 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 |
Posted By: Capt Fiero
Date Posted: 20 August 2012 at 12:09pm
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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. |