Obviously it should not, but mine does - as long as the battery is good, i hear the fuel pump humming whether the key is in the ignition or not. This is only since getting the new engine/clutch/etc. installed. Since this would clearly kill the battery, i pull the fuel pump fuse when i park it, but that's a hassle (great anti-theft though!)......what the heck would cause it to runn at all times??
This is on an '88 Fiero Formula 5-speed.

Sounds like your fuel pump relay is either bad or got wired wrong. Was any re-wiring done for the new engine ?

it is either your fuel pump relay or the oil pressure switch. it usually is the oil pressure switch. i dont think the duke uses the newer updated oil presssure switch the the 88 2.8's do.

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First LX9 Fiero GT, 1987

If you can't fix it with a hammer, you've got an electrical problem

It is a 2.8L V6, more or less stock but with a little head work and a slightly hotter cam. When i bought the car it had a rod knock, but i sourced a date-correct long block still in the crate. All the accessories were replaced as well, so mechanically it's "all new"....i didn't do the work though, so i can't say for sure on the wiring. Where is the FP relay?
Sorry if it's a dumb question but what could the Oil Pressure switch have to do with it? I know the Oil Pressure gauge acts crazy...?

quote Originally posted by FieroFan88: Sorry if it's a dumb question but what could the Oil Pressure switch have to do with it? I know the Oil Pressure gauge acts crazy...?

The oil pressure switch is a backup for the fuel pump relay. If the relay is bad, the oil pressure switch will activate the fuel pump after a few seconds of cranking (when oil pressure rises past a certain point).

Fuel Pump relay is right behind the driver on the firewall there are two there, dont remember which one it is. The oil pressure sender has to see pressure to allow the fuel pump to run.

If you have AC I know there is 2 there for sure. It is located right behind the air filter can (you have to take that off). One is the fuel pump relay the other is for the AC and both are identical. Just switch the plug from one to the other and if the problem goes away your set. Just get a new relay or leave it if your AC don't work anyway. Good Luck

Unplug the oil pressure switch, if that stops it (and 99% it will) you need a new switch and a new relay. The normal scenario for this failure mode is that the relay failed and the secondary contacts in the switch take over turning on the fuel pump. Symptom of this is that it takes a few seconds of cranking before the engine starts. The contacts aren't designed to do this full time and eventually fail, typically by welding the contacts closed. With the switch disconnected the fuel pump will only run for 2 seconds when the key is first turned to RUN but not to START. If it doesn't do this either the relay is bad (common) or the ECM relay driver is blown (rare).

The circuit:



JazzMan

quote Originally posted by Riddick85: If you have AC I know there is 2 there for sure. It is located right behind the air filter can (you have to take that off). One is the fuel pump relay the other is for the AC and both are identical. Just switch the plug from one to the other and if the problem goes away your set. Just get a new relay or leave it if your AC don't work anyway. Good Luck

Interesting - thanks, i'll try that. Yes it "has" a/c but i don't even know if it works, nor do i care since the DD's have air

Oil pressure is not needed for the pump to run.

Upon turning on the ignition, whether cranking or not, the ECU will power up the relay and hence the fuel pump for about 3 to 5 seconds to build pressure. When the engine cranks the ECU receives a signal from the ignition system which tells it the engine is running and the fuel pump relay is energized and will run all the time the engine is running. If the relay fails or the ECU fails or there is no signal from the ignition then there is a oil pressure switch which will sense the buildup of oil pressure and will power the fuel pump directly. I believe it bypasses the relay. The switch will fail if it has to carry the current for too long. An engine warning light and a code in the ECU should tell you what has failed so it can be repaired.

I am not sure if the oil pressure switch and the sender for the gauge are the same, they may be different units as one varies resistance for the gauge and one is a simple on/off switch for the fuel pump back-up and my car and manual are both at home.

If the fuel pump runs all the time without starting the engine it could be the relay which I believe is usually the one on the right. The AC is, I believe on the left normally.

I hope this helps a little.

quote Originally posted by JazzMan: Unplug the oil pressure switch, if that stops it (and 99% it will) you need a new switch and a new relay. The normal scenario for this failure mode is that the relay failed and the secondary contacts in the switch take over turning on the fuel pump. Symptom of this is that it takes a few seconds of cranking before the engine starts. The contacts aren't designed to do this full time and eventually fail, typically by welding the contacts closed. With the switch disconnected the fuel pump will only run for 2 seconds when the key is first turned to RUN but not to START. If it doesn't do this either the relay is bad (common) or the ECM relay driver is blown (rare). JazzMan

Thanks! No it's always started pretty much instantly, even after sitting a long time. That reminds me though - it also has a new ECM.

has it fired up after the new ECM was put in? before this fuel pump problem?

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First LX9 Fiero GT, 1987

If you can't fix it with a hammer, you've got an electrical problem

quote Originally posted by garage monster: Oil pressure is not needed for the pump to run. Upon turning on the ignition, whether cranking or not, the ECU will power up the relay and hence the fuel pump for about 3 to 5 seconds to build pressure. When the engine cranks the ECU receives a signal from the ignition system which tells it the engine is running and the fuel pump relay is energized and will run all the time the engine is running. If the relay fails or the ECU fails or there is no signal from the ignition then there is a oil pressure switch which will sense the buildup of oil pressure and will power the fuel pump directly. I believe it bypasses the relay. The switch will fail if it has to carry the current for too long. An engine warning light and a code in the ECU should tell you what has failed so it can be repaired. I am not sure if the oil pressure switch and the sender for the gauge are the same, they may be different units as one varies resistance for the gauge and one is a simple on/off switch for the fuel pump back-up and my car and manual are both at home. If the fuel pump runs all the time without starting the engine it could be the relay which I believe is usually the one on the right. The AC is, I believe on the left normally. I hope this helps a little.

Mostly correct. The oil pressure switch contacts are in parallel with the relay contacts, that means that either will provide a path for power to reach the pump. Normally the ECM commands the relay for just under 2 seconds upon turning the key to RUN in order to prime the injectors, and immediately turns the relay on when it sees the distributor turning via EST pulses from the module. Because of this, the pressure switch contacts never really see any current when they close and open. The normal failure mode for the relay is off, typically because the windings failed. The most common failure mode for the oil pressure switch is on by welding the contacts, they are very much too light duty to do this job full-time.

The pressure switch for the fuel pump, the oil light, and the resistance wiper for the guage are all built into the same sender housing.

The ECM does not contain any ability to sense when the fuel pump-related circuitry has failed; the only connection between the fuel pump circuitry and the ECM is the relay driver wire.

JazzMan

quote Originally posted by americasfuture2k: has it fired up after the new ECM was put in? before this fuel pump problem?

I imagine, at the Pontiac Dealer.....here's the story: i've owned this car forever, like over 10 years, but it was one of those projects that was a low priority and it just sat covered for a long time. I had this car before either of my wives or any of my 3 kids. Finally within the past couple years i had a local "Fiero expert" do all the engine work, but the shift action was a mess, turns out it also needed new shifter cables which other local shops were scared of and said the dealer was my best bet. Even with the new engine, it wasn't running so great, so i asked the dealer to figure THAT out while they had it - that's when they figured out it needed the new ECM. Now it runs fantastic.
I don't like where you're going with this, though, because IF the problem is the new ECM, i'm screwed because that Pontiac dealer is now out of business! I am really hoping my problem is the relay because the bottom line is i have already sunk way more money into this toy than is reasonable...

It only takes about five minutes to do the bulk of diagnosis of the fuel pump system in a Fiero. In your case, just unplug the oil pressure sender, it's by the water pump:



If the pump shuts off you've found the problem. If not, leave it unplugged and unplug the relay:



If it still runs you've got damaged wiring, if not then you need to replace the relay. With the relay out, plug the oil pressure sender back in, if it starts running again then the sender is bad too, replace it.

These two tests rule out the relays and switches. To check the ECM, just leave the relay and switch disconnected and use a test light connected to ground to probe terminal A of the relay connector:



or the Fuel Pump Terminal in the ALDL connector behind the cigarette lighter trim plate:



With the test light tip in the terminal, you should see the light come on for about two seconds when you turn the key to RUN but don't crank.

The fuel system in the Fiero is really simple.

JazzMan