Crazy Fuel Pump Wiring?

BMAN · 07-11-2012, 05:47 PM

Really not sure what's going on here but I know I'm got going to keep it that way. The wire runs from the fuel pump relay to the negative side of the battery (Ground) Does anyone have a fuel pump wiring diagram so I try to figure out what has happened here.

One thing I noticed, when I turn the key to the on position engine not running the fuel pump runs and will not shut off until I turn the key off.

billjam · billjam's Garage

This wiring diagram might help. It has only the wiring and electrical components related to the fuel system, which makes it easier to figure out which points can be jumped to bypass relays or dud connections.
As it says, it is for an '86 930, but I think most models are fairly similar. If anyone wants a clear PDF version or the original Visio file, email me your email address.

billjam · billjam's Garage

Actually, this one might be easier for you. I just greyed out the '86-on components, so what's left should be close to what you have on your '85. I don't have any details of where the white wire from the over-boost switch runs, so this is my best guess.
Anyone with better info, please let me know and I'll update the drawing if necessary.

Tt surgeon · 07-12-2012, 06:48 AM

Mine has nothing like that wire. Perhaps it's part of some aftermarket alarm that shuts off the fuel pumps?

billjam · billjam's Garage

Quote:

Originally Posted by Tt surgeon

Mine has nothing like that wire. Perhaps it's part of some aftermarket alarm that shuts off the fuel pumps?

The over-boost switch (aka charging pressure control switch, or charge pressure safety switch) is definitely standard on 930s from 86 on, and I'm pretty sure it is also on all earlier models. It has nothing to do with alarms; it shuts down the engine if boost exceeds 1.5 bar by cutting the ground to the fuel pump relays solenoid coils (terminals 85).

JFairman · 07-12-2012, 07:06 AM

The fuel pump relays are the two red ones at the rear end of the front relay panel. They should be red ones anyway.
The one all the way at the rear end closest to the windsheild is for the rear fuel pump, and bimetallic spring heating elements in the cold start WUR and aux. air valve.

Your blurry pic is so close up it's hard to tell what part of the relay panel is in the frame but if thats the front fuel pump relay with the yellow wire stuffed into a ground pin then it looks like someone's quick rig to get the fuel punps running. Possibly because of bad contacts on one of the other relays or relay sockets in the fuel pump relay chain from hell.

The factory alarm system will disable the fuel pump relays along with blasting the horn on the front crossmember if it's armed and a door or the front trunk is opened far enough to turn on the interior light switches, so it's connected into that wiring schematic somewhere too. Probably to one of the relay ground wires.. could even be part of the problem.
Open a door or the front trunk far enough to trigger the interior light switches and the horn on the front crossmember will start blasting and the fuel pumps will not run if it works.

Quote:

Originally Posted by BMAN

Really not sure what's going on here but I know I'm got going to keep it that way. The wire runs from the fuel pump relay to the negative side of the battery (Ground) Does anyone have a fuel pump wiring diagram so I try to figure out what has happened here.

One thing I noticed, when I turn the key to the on position engine not running the fuel pump runs and will not shut off until I turn the key off.

Tt surgeon · 07-12-2012, 07:23 AM

Quote:

Originally Posted by billjam

The over-boost switch (aka charging pressure control switch, or charge pressure safety switch) is definitely standard on 930s from 86 on, and I'm pretty sure it is also on all earlier models. It has nothing to do with alarms; it shuts down the engine if boost exceeds 1.5 bar by cutting the ground to the fuel pump relays solenoid coils (terminals 85).

I realize that, I was referring to the yellow wire tapped into the relay itself.

BMAN · 07-12-2012, 03:47 PM

Thanks for the info guys. The one good thing is its only a ground. This weekend I'll pull the fuse box off the fender to see what's going on. My old 86 930 had two black relays also not red.

BMAN · 08-04-2012, 08:07 AM

Got a chance to look into it today, the yellow wire definitely is ground but the weird thing is once I remove it from the relay the cars starts right up. I know the car has two fuel pumps, would the car start up with only one working? If not I can't imagine why someone would ground it like that.

The other good thing now is when I turn the key to the 1st position the fuel pumps don't run like before until you start the car.

rrental · rrental's Garage

Quote:

Originally Posted by BMAN

Got a chance to look into it today, the yellow wire definitely is ground but the weird thing is once I remove it from the relay the cars starts right up. I know the car has two fuel pumps, would the car start up with only one working? If not I can't imagine why someone would ground it like that.

The other good thing now is when I turn the key to the 1st position the fuel pumps don't run like before until you start the car.

Be careful here...I had a problem a few weeks ago with a non starting car. The shop did some emergency wiring to get me going fast. All they did is bypass the problem in roughly the same way as in your car.

In my case it seems the over boost switch has to be replaced. While waiting for the switch I played around a bit and brought it back to original, and the car started, no problem. But is was only for a bit. The switch got a mind on its own! Keeps cutting in and out. Fortunately I documented the fix and could bring it back to life in minutes.

BMAN · 08-04-2012, 01:52 PM

If one pump is only working should my car start?

BMAN · 08-05-2012, 11:38 AM

From my search that relay controls the front fuel pump. I put the car on jack stands and started the car with the yellow ground wire disconnected, the front pump works, I pulled the relay and the car turned off.

I tried to listen for the rear pump but with the engine running it was tough but I put my hand on the fuel line and I could feel the flow.

I wanted to take a look at the yellow relay in the rear but when I removed the cover this is what I found. When I traced the wires they went under the front drives seat, looks like someone removed some kind of ECU. The white wire went to the 02 sensor so now its not hook to any wire and I couldn't find the stock wire that it should plug into.

I took the car for a drive and hit boost a few times with no issues, If only one pump was working would I be able to tell while driving?

Those wire went here, not plugged into anything

Pulled all of it out.

Not sure what this harness is? They should be plugged in together.

Its goes here.