ABY low volts to fuel pump

[martinjs]

The car won't start due to the fuel pump only getting 8.8v.
I bought the car with the engine out so after slowly putting it back together it did actually start fine, it was stood for a week or so after the mot then this fault occurred.

With the pump wired direct to the battery it starts ok.

Across the 2 large relay terminals in the fuse box there is 12v with ignition off, this drops to 10v when cranking.

I'm not that good with electrics btw.

[AndyP]

I take it the battery has a full charge? Have you checked all the earth points?

[quattrodave]

Its probably the supply wire that runs through the car from the fusebox thats past its best, I had to change it on our 10v coupe quattro at about 150k miles (was a very early 1988 registered b3 coupe that had gone through 3 pumps in the 10 years before I replaced the wire) when it was about 15 years old as the original wire was very brittle and showing such high resistance it was only getting very low voltage at the pump, its a common issue with the B3/4 coupes.

Run a new supply wire to the pump fromthe original point in the fuse box (also check the fuse box connections are still ok)

[martinjs]

Battery is new, the proper engine Earth strap was missing so I ran another from the bellhousing to an earth point near the abs unit.
There are no other electrical issues.
I'm guessing I need to fit an original strap and go from there?

[martinjs]

Its probably the supply wire that runs through the car from the fusebox thats past its best, I had to change it on our 10v coupe quattro at about 150k miles (was a very early 1988 registered b3 coupe that had gone through 3 pumps in the 10 years before I replaced the wire) when it was about 15 years old as the original wire was very brittle and showing such high resistance it was only getting very low voltage at the pump, its a common issue with the B3/4 coupes.

Run a new supply wire to the pump fromthe original point in the fuse box (also check the fuse box connections are still ok)

Ill try that along with the correct Earth strap.
Battery, fuel pump, alternator are new, car has done 77k

[newsh]

Or use the original wire to close a relay under the rear seat to power the pump straight from the battery. [emoji6]

[UrS4boy]

How to "Turbo Charge" your Fuel Pump: Battery to Fuel Pump Relay DIY

Or use the original wire to close a relay under the rear seat to power the pump straight from the battery. [emoji6]

One could follow my AAN-based DIY and make it work for an ABY/ADU:

How to "Turbo Charge" your Fuel Pump: DIY instructions for adding a battery-to-fuel pump relay:

http://forums.quattroworld.com/s4s6/msgs/24327.phtml

[Rikki Kitto]

I need to do this so thanks for the info, fitted a bosch ages ago and didn't bother with the wire upgrade so now i can give it a go

[martinjs]

Think I'll do the relay mod.

[mcandmar]

I highly recommend a direct feed from battery via a relay, with the 044 pump i was losing over a volt through the stock wiring harness.

As to martinjs original issue, i would start by checking out the fuel pump replay for dirty contacts, it may even be a dodgy relay itself. If the inside of your fusebox is damp i would lay money on that being the issue.

[martinjs]

I've tried 3 different relays, no change.

[M_GORDON]

Firstly try with a direct grownd wire.

later, if this no works... you must change all the wires and maybe better, put other relay from the battery

[M_GORDON]

rep...

[s2dk]

One could follow my AAN-based DIY and make it work for an ABY/ADU:

How to "Turbo Charge" your Fuel Pump: DIY instructions for adding a battery-to-fuel pump relay:

http://forums.quattroworld.com/s4s6/msgs/24327.phtml

hey could u maybe draw a skets on the wirering ?

[UrS4boy]

hey could u maybe draw a skets on the wirering ?

No but I googled "fuel pump relay wiring sketch" and found the perfect one for my DIY description. You use the OE fuel pump power wire from the OE fuel pump relay to trigger the second relay located nearer to the battery and the pump: