tpi90rs

iTrader: (2)

so like the title says, my ignition is off, the fuel pump relay is unplugged and the fuel pump is still running.

what would cause this?

I had turned my car off, the pump went off and I went inside then (my neighbor came over telling me I had a back tire going flat) the pump was on an hour later. I didn't even touch anything.

'87 MAF TPI 350

tpi90rs

iTrader: (2)

or just tell me what page the fuel pump wiring is on in an '87 service manual, I can't find ****!

cIaRmOaCrZo

yeah it sounds like you have a short to power somewhere. but im sorry i cant help you with a page number, i dont have that book. and im already graduated from my school that had full access to alldata, so cant help you there either. and my boss prolly wouldnt like me using his alldata for anything other than work lol. but yeah if you could get the wiring diagram, it should be cake to rewire the fuel pump circuit.

camaronewbie

Oil Pressure Sending Unit (OPSU) is bad - replace it.

Fuel pump gets current through two independant sources, 1) the ECM sends signal to the fuel pump relay, and 2) OPSU gets power directly from battery to fuel pump.

Pump running constantly means that the OPSU "thinks" there's oil pressure when there's really none, and thus it's running the fuel pump directly off the battery - so makes no difference whether key is in, or on, or in your pocket.

Beside the battery, tucked in the fenderwell, there will be a fuse inside a weatherpack - pull that fuse to make the pump stop temporarily. Put fuse back in to drive. This will disrupt that circuit without disconnecting battery and disturbing radio presets etc. until you can get it fixed.

OPSU is either 1) above oil filter in the side of the block, or 2) on top of the china wall at the back of the intake on driver side of the distributor.

About $30 depending on which one you need for your year car.

cIaRmOaCrZo

damn, i think you might have hit right on the nose lol, i cant believe i overlooked that senerio. which eventually would have been revealed through a series of pinpoint test.

you should change your profile name, cuz you dont sound like a newbie haha

tpi90rs

iTrader: (2)

****! I replaced that 2 years ago and it's a bitch to get out with my headers.

I thought the OPSU goes to the ECM and the ECM controls the relay? because if the car doesn't have any oil pressure it should shut off the fuel pump and kill the engine right?

Edit: NVM, Thanks newbie! I over looked the OPSU on the schematic I was looking at

camaronewbie

There's debate as to whether the OPSU cuts off the fuel in event of no oil, or if the OPSU cuts on the fuel in the event of no ECM.

But I can tell you from personal experience that the OPSU can go bad and make the pump run until the battery is dead - my 1992 RS had this problem when I first got it, and it took me some time to figure out why my battery was dead every 3-4 days.

vetteoz

iTrader: (13)

Popular wrong belief.
Switch is only there to backup pump relay should it fail and is wired direct to the pump.( also has a link to the ECM so it knows pump is running when cranking )
In any case at the 4psi the OPSU opens at your engine would be cactus before it shut down.

Damon

Agreed- OPSU is battery voltage on one side, straight to the fuel pump on the other. No other switches involved that can turn it off.

I know this from experience priming up the oil system on new engines. Everything hooked up, key off, when the oil system primes up and generates oil pressure the fuel pump kicks on (which can be surprising if you haven't hook up the fuel lines to anything yet!!).

FireDemonSiC

camaronewbie: Could this same logic cause a car to be difficult to start due to insufficient current to the fuel pimp?

For awhile now, my car has had a starting issue. Off a cold start, you have to crank and crank and crank before it will start. After an immidiate shutdown, the engine hesitates for a second but then starts up. The sweet spot is about 1 - 2 hours after you've shut the car off. The second you turn the key it fires right up. Also note that when you start it, "in the sweet spot", the fuel pump sounds like It's priming much stronger and quicker.

Please help! Been trying to figure this problem out for over a year now!

Pocket

iTrader: (24)

No, that sounds like a bad IGN module. If the pump sounds louder after its cooled off, it may be on its way out

Simple fix to the oil pressure switch is to unplug it. Then you directly rely on the relay to control fuel pump function. Later cars combined the switch and gauge sender into one unit, those require wire snipping to get around