babyelephant

1987 Trans Am GTA 5,7 TPI auto, with digital dash.

What causes the fuel pump to run at all time the ignition switch is activated? It doesn't stop after a few seconds, but runs until car stop/ignition shut.

Tests performed:
1. Fuel pressure measured 44 with ignition on, drops to 36 after startup. Keeps pressure after ignition off. Should be OK ref Haynes.
2. Activated terminal G at OBD-port, fuel pump engages.
3. Pulled fuse 2 for fuel pump makes no difference.
4. Pulled fuel pump relay makes no difference.
5. Unclipped oil pressure switch above oil filter makes no difference. (don't know if, either)
6. Pulled wiring clip above rear diff/fuel tank, yes, makes it stop.
7. Fuel filter is brand new AC Delco part.

I haven't the complete history on this car. Is there an obvious reason, a switch or sensor that goes bad? I've searched the forum for similar problems and learned of cars which fuel pump has been hardwired to the ignition for some reason. May have happened to my car too? That may affect the lifetime of the pump negative?

LiquidBlue

If you're pulling all the fuses and relays that should disengage the pump, then it sounds like someone has bypassed those somewhere.

SbFormula

That is weird! Fuel pump cannot operate without relay.

Are you sure you are pulling the fuel pump relay or the fan relay?

Fuel pump relay could be stuck in closed circuit

babyelephant

makes me think, There are three relays on the driver’s side firewall and I was told FP is the one closest to dizzy. (The one in middle states MAF). I will check wire colors if they are swapped (if possible)

Vader

Actually, the fuel pump can run without the relay. The oil pressure switch is in place specifically for that purpose.

Check the oil pressure switch at the rear ledge of the block, just behind the intake on the left side.

Vader

This is the common relay arrangement:

SbFormula

SbFormula

Oups!! you’re right.
I forgot about that. thought the oil pressure switch was controlling the relay... which would make no sense!
Cheers

babyelephant

Haven't had time to work on this topic for some days. Sorry guys for confusing you, but apparently my fuel pump relay is located closest to fender. The fuel pump indeed cut when pulling this! The numbers crossreferenced (Rock Auto page) with the relay closest to distributor, so I tried to swap them, but made no difference as the fuel pump kept on spinning for as long as ignition is on.

I did also pull the oil pressure sending unit above the filter, and mounted a new from Standard (only one available local). No difference.

I don't know my next step...

Thank you. I think my car differ a bit from your picture? You mention a pressure switch, is it the same as the oil pressure sending unit/switch located above the oil filter?
​​​​​​​The gauge sender behind the distributor, I replaced two weeks ago, due to wrong reading in my digital dash (solved this).