how can I bypass the fuel pump relay or how jump fuel pump?

CaifanSC · Apr 14, 2011

Hi guys,

Unfortunatelly I dont have my bentley manual with me at work. I'm trying to help my mechanic diagnose an 86 audi 5000s from a few thousand miles away. The problem right now seems to be that there is no fuel pressure. The mechanic can't hear the fuel pump priming when the key is turned and even while cranking and one of the fuel hoses disconnected there is no fuel gushing out of the fuel filter lines. The fuel pump was replaced a couple years ago so i'd like to first discard the posibility of a faulty pump. Can anyone point out where I can jump so that the fuel pump comes on? Is my only option doing this at the actual fuel pump terminals?

thanks guys.

Val · Apr 14, 2011

You could jump 2 biggest fuel pump relay legs together and push relay in relay holder. Also, 5000 should have the same fuse box as 4000, it had #13 fuse for fuel pump.

boschman36 · Apr 14, 2011

Take the fuel pump relay out, throw one of the grey a/c ones in (far right side of the panel) and put that in. Turn the key to the run position, it will jump the pump to run.

CaifanSC · Apr 14, 2011

if I recall correctly the top of the fuse box has the layouts pointing which relay is for what correct? Sorry for what seems to be noob questions but it's hard since I don't have the car in front of me.

Val · Apr 14, 2011

Relay = J
Fuse = 13

CaifanSC · Apr 14, 2011

excellent! thanks for the diagram.

I'm gonna check fuse 13 first, then swap F/K for J and then crank.

That should at least discard a faulty pump.

elaw · Apr 14, 2011

Actually after you've swapped the relay, you shouldn't even need to crank. Just turn the ignition to "run" and listen for the pump running. If you hear it, *then* crank... with your fingers crossed!

Also, if the setup is the same as a 4KQ of the same age (and I think it is), the fuel pump relay has larger terminals than the other relays. So another relay isn't going to make very good contact and I wouldn't advise driving the car that way, it's only useful as a test.

CaifanSC · Apr 15, 2011

thanks for the replies guys, i'll hear about the results tomorrow.

Katman · Apr 15, 2011

elaw said:
Actually after you've swapped the relay, you shouldn't even need to crank. Just turn the ignition to "run" and listen for the pump running. If you hear it, *then* crank... with your fingers crossed!

Also, if the setup is the same as a 4KQ of the same age (and I think it is), the fuel pump relay has larger terminals than the other relays. So another relay isn't going to make very good contact and I wouldn't advise driving the car that way, it's only useful as a test.

In a 4k, you can use the 'X' (or 'load reduction') relay in place of the FP relay, as it DOES have the big termainals, and does exactly as you mention above. (Runs pump as soon as you turn on ignition...) Probably the same on a non turbo 5k.

(However, I'm thinking that trick won't work in the turbo 5k, as the ECU turns on the fuel pump there. But in that case (if you have the 5k FP relay with the fuse on top), you can run the 'output tests' which turn on the pump anyway..)

Output tests: http://www.sjmautotechnik.com/trouble_shooting/ecuf.html#out1

how can I bypass the fuel pump relay or how jump fuel pump?

CaifanSC

Val

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