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9/22/2017 12:11:25 AM
Posted: 9/15/2005 4:07:25 PM EDT
Project car:

Fuel Pump NOT getting power. I have a multi-meter hooked up to the pump, and also am listening for noise. I know the fuel pump is good--I can hook up an outside battery to it and it runs fine. (Car starts and runs also). I tried a couple of things (has an OLD factory alarm system that disables the fuel pump)..Jumpered to disable the Factory Alarm...no dice.

Fuel Pump relay--jumpered...still no power to fuel pump.

EFI relay--jumpered..still no power to fuel pump.

Tried jumpering all three at once...nothing.

Checked wiring on Fuel Pump--fine...HOWEVER..the ground wire insulator is melted. Pulled both + & - wires off...will replace ground all the way to the ground point.

Tried to see if I could get Voltage to the + wire (looks fine) on turning the key to run and over to start..still no power (Multimeter hooked to + wire and chassis ground)...didn't get anything yet.

So, if I cannot sort it out, I may just run power directly to the Fuel Pump..

If I need to...will run from battery to fuel pump...switch near driver somewhere. I'll put a fuse in line to be sure no problems with the fuel pump frying..

Any recommendations on how to wire in a switch if I need to? I want something with a light--hopefully, I won't forget to turn it off if there is a lighted switch. Run Fuel Pump to Ground, run red wire from + battery to switch, then to + terminal on fuel pump?

Rather have it work properly, but if I cannot get the relays/factory wiring to work correctly, then I have to do something.


Link Posted: 9/15/2005 4:18:31 PM EDT
If you rig it you would be better off running it off of a wire that is only live with the ignition switch on than running a toggle switch. That way when you turn the ignition on the pump runs. With a toggle you have a much better chance of forgetting to turn it off.
Link Posted: 9/15/2005 4:29:50 PM EDT
Good Point.

Have any suggestions as to where to tap that kind of power? Don't want to short anything on power.
Link Posted: 9/15/2005 4:44:26 PM EDT
[Last Edit: 9/15/2005 4:45:24 PM EDT by turbo_infidel]
I dont sugest hooking something like a fuel pump up to a switch that the driver controls.

your relays
should have

B+ on pin # 30
ground on pin #85
pump should be pin # 87

and the trigger should be pin #86

assuming that the trigger is a B+ and not ground.

so were checking that the terminal #30 has B+ all the time and is fused

#85 should have a good ground

pump and #87 should have continunity and the pump should have a dedicated ground
and you should see 12 volts at pin # 86 for a few seconds when you turn on the key

Link Posted: 9/15/2005 4:49:49 PM EDT
B+ (not understanding the term)?

My Relay for the Fuel Pump has a #30 and a #87 (30 is hot all the time)--these are the main connections that the relay bridges. I tried jumpering 30 to 87 and still got no power to the pump.

Link Posted: 9/15/2005 4:57:12 PM EDT
[Last Edit: 9/15/2005 4:58:27 PM EDT by Minuteman419]
Some vehicles have an oil pressure switch that shuts down the fuel pump in the event of loss of engine oil pressure.

I've seen these switches go bad on GM products before and cause headaches.

Also seen inertia switches on Ford's get tripped easily.


Link Posted: 9/15/2005 5:04:08 PM EDT

B+ means 12 volts or what ever you battery is
Link Posted: 9/15/2005 5:07:52 PM EDT
if you can jump # 30 and # 87 and still not have the pump turn on.

take your multi meter to the pump jump 30 and 87 and check for B+ at the pump,
if it is not there theres a supply (wire) problembetween the relay and the pump,
if there is B+ at the pump , check for a ground problem at the pump
Link Posted: 9/15/2005 6:03:24 PM EDT
12 Volts at #30 on Fuel Relay.

NO power at Green/Red wire (to pump), either where it enters the wiring plug (relay board) OR the terminal end at the pump.

Link Posted: 9/15/2005 6:24:21 PM EDT
sounds like a bad relay check to see if you remove the relay and jump #30 and #87 (the two heavy gauge wires ) witha spare piece of wire if the pump turns on the relay is probably bad

need to verify the relay is switching use the multi meter
remove wires 30 and 87 from the relay carefull one is hot (b+)

switch the relay on and measure for continunity between 87 and 30 should make a clicking sound

good luck
Link Posted: 9/15/2005 6:30:45 PM EDT
What kind of car are you working on?
Link Posted: 9/15/2005 8:12:33 PM EDT
928s 1984. Got it basically free (traded some stuff of no real value for it...)

Trying to get it running.

I have tried jumping the 30 to 87 already--no dice. I'm going to trace forward (from the Hot at 30 on the FP relay) towards the Fuel Pump. Find the Break.

Have a Wiring Diagram---looks more like 5 Pounds of various varieties of pasta thrown together..
Link Posted: 9/17/2005 2:22:52 PM EDT
[Last Edit: 9/17/2005 2:31:08 PM EDT by oneshot1kill]

Originally Posted By AFARR:
928s 1984. Got it basically free (traded some stuff of no real value for it...)

Trying to get it running.

I have tried jumping the 30 to 87 already--no dice. I'm going to trace forward (from the Hot at 30 on the FP relay) towards the Fuel Pump. Find the Break.

Have a Wiring Diagram---looks more like 5 Pounds of various varieties of pasta thrown together..

If the relay clicked when you jumped it between 30 and 87 then it's(relay) good and your problem is a likely a short/open to the pump(as indicated by the melted insulation).
Link Posted: 9/18/2005 8:41:53 AM EDT
Checked my wiring diagram for a '84 928S.

Your FP relay has a Red/Green wire coming off terminal #87. This wire is the suspected short/open wire as it goes right to the pump to supply battery voltage. It is also fused, fuse # 13 on you fuse box, make sure it's still good, you could have popped it when you jumped out the relays earlier. Wire color can vary but generally this is the color Porsche used for that circuit, in any event it's the same wire that comes off #87 on the FP relay.

If the fuel pump relay 'clicks' when you jumped it out between 30 and 87, check for power at the Red/Grn wire (at the relay #87). You should have power. If not the relay is bad. I think we already established that it is good, correct? Make sure though.

If the relay clicks and you have power on #87 at the relay -but not on the pump- then you must replace the Red/Grn wire.

Remember, the ful pump itself has two wires, a Brown ground wire that goes right from the pump to a good chassis ground, and the power wire that goes from the Fuel Pump Relay #87 to the pump.

Use your multimeter to check the Red/Grn power wire for short/open. If it's bad then cut the old wire(leave some wire on either end to splice) and run a new wire directly from relay (#87)to the fuel pump. While you are at it replace the ground wire(you said it was melted at insulation) Run a new ground wire to a good clean spot on the chassis.

OR an alternate method...

1)- Disconnect battery

2)- Make sure fuel pump ground wire(Brown) is good and not damaged, if not replace this wire first.
Run new wire directly from fuel pump right to chassis, wherever you can find a good clean spot. You mentioned that it was damaged earlier so just replace it now to prevent another short.

3)- Take a long jumper wire and connect it between FP Relay #87 and the power side of the pump (Red/Grn wire).

4)- Don't jump out the relay, just from relay #87 to pump power.

5)-Reconnect battery

6)- Check fuse #13.

7)- turn ignition on and pump should work now, but keep in mind that many fuel pumps only get power with ignition on -not cranking- for only a few seconds.

If the pump comes on now -and it better- then you just need to re-do step #3 using a new wire instead of a jumper wire.

Good Luck, keep us posted.

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