hello there. My 85 2.8 fuel pump runs constantly with the key on...It will shut off with key off...I replaced a bad fuel pump and I have the sending unit sitting in the engine bay testing before installing...When I turn the key on fuel pump is working but doesn't shut off after 2 to 5 seconds...Is that normal? Things I have tried are unplugging the relay and oil sending unit same time and no change...I've swapped the relay with a known good one..No change.. It does have a remanufactured ecm from napa...Anything I can troubleshoot further? Thank You

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James 1986 Fiero SE V6 2.8
Central Florida

[This message has been edited by jaydaug2008 (edited 12-08-2023).]

Unplug you oil pressure sending unit. Its used as a bypass to keep the engine running if your relay dies. Sometimes they get stuck open. If you unplug it and it stops replace it

Yeah but ive tried that...unplugged the relay and sending unit same time and still runs...

You sure it's really the F-pump? Or pulled right relay plug?

Pull both relays as AC clutch is same type. But carefully watch w/ plug to which relay.

85 F-pump relay has:
wht/blk main power
tan/wht to pump
dr grn/wht from ECM to coil.
blk to coil ground

If relay is bad, use AC Clutch relay to fix right now then buy new ones.

If pumps keeps running w/o relay & oil sender....
tan/wht is shorted to "12v" somewhere & that wire doesn't have a fuse or other way to kill it but discon C502 on "firewall" from bulkhead wire "plugs" to the tank that's often hard to see in V6 cars.
Or pull the battery cable.
Because F-pump & other motors will kill the battery fast.

Open the hood & check HL motors are Off & stay Off. Gen1 HL motors can Fail & run all the time or "twitching" as Breakers in the motors keeps cycling.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Well I actually was unplugging the wrong relay and found it, unplugged it and swapped it with the relay next to it and same thing still continues to run constantly...what do you suggest I check now..

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James 1986 Fiero SE V6 2.8
Central Florida

Runs with either Relay in?
Then have wiring or ECM bad.

Wire from ECM to Coil is just that. nothing else. Is one of or the shortest circuit in the car w/ only 2 plugs & maybe 3 feet of wire.
Unplug the ECM. If still runs check wire harness didn't melt from exhaust leaks etc.

Make sure all Grounds bolted to engine is good & clean connections. Coat w/ silicoe or brake grease to keep water out.
Because rare chance a ground is crap something else try to backfeed the coilIf that happens, need 2 new relays because backfeed can fry protected Diodes in them that normally is surge protection from the coils.
I've never seen a sneak path doing this but anything is possible. See https://web.archive.org/web...rocave/sneakpath.htm

ECM won't keep the F-pump running unless engine starts/runs. Iffy ECM can stay On. Maybe a few other things may trick the ECM telling like key switch is starting etc.

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Until you unplug the fuel pump/sender from the wiring harness, we don't know for sure that it's indeed the fuel pump that's running.

[EDIT] Or is the fuel pump sitting there in front of you? If so, I hope you haven't been letting it run while dry.

quote Originally posted by jaydaug2008: I replaced a bad fuel pump and I have the sending unit sitting in the engine bay testing before installing...

[This message has been edited by Patrick (edited 12-08-2023).]

If the fuel pump runs constantly every time the key is on, without the relay and oil pressure connectors connected, then there has to be a jumper wire or direct short between the fuel pump feed wire and a 12V key source. This short or jumper would have to be between the relay connector and fuel pump, oil sender and fuel pump, ALDL (has a fuel pump wire) or someone ran another 12V wire to the fuel pump connector.

Does pulling the fuel pump fuse make it stop? If it does, then at least you know the jumper is off the fuel pump fuse feed. If it doesn't continue to pull fuses until you find the one that makes it stop. That will help you narrow down the likely position for a short or jumper wire.


Assuming the fuel pump fuse does stop the power to the fuel pump, I would pull back the wiring loom to the fuel pump relay, the oil pump connector, to the fuel pump connector, and pull the console and check the ALDL wiring.

I am so sorry fellas.....I totally botched this post with inaccurate information and I need to restart a new thread about this....I am seriously so sorry for having you scratch your heads on that because I was messing with the wrong relays and thats why nothing makes sense...I was swapping and messing with the relays under the front hood OMGGGGGG this whole time....I will be buying OGRE a few beers because if it wasnt for him and all you regulars conquering everyone problems like you do. I would be lost and so would everybody else..Please allow me to start fresh with the correct info again...This website deserves a beer!! It can never go down!!

Yes, those relays are in engine bay....
Don't start a new thread for same problem.

Just follow above relay switch. If needed take 1 of same relay front to rear & know what every won't work w/o it...
Example: High Speed Heater blower is same & only affect high speed w/o this.

Many years ago my 85 SE V6 fuel pump started running all the time; The oil pressure sending unit has wiring that keeps the fuel pump running if there is oil pressure and the key is "on" and sometimes it becomes defective and starts running all the time....Sounds kind of odd, but the guy who told me this was very knowledgeable about Fieros....changed out the oil pressure sending unit and problem went away.

Many years later I was experiencing a lot of oil leakage from the oil pressure sender, so a known fix/improvement is to change over to the 88 sending unit- better design that is lacking the idiotic design flaw that causes leakage (Even when the sender is tight)....You do have to swap the plug also, though....

[This message has been edited by cvxjet (edited 12-30-2023).]

yes, old sender often leaks thru the insides even when they work otherwise. Worse get oil pressure until sender leak has drain the oil pan.
88 sender can break but don't leak oil like old design.

88 oil sender upgrade...
https://web.archive.org/web...rocave/oilsender.htm