S8 No start fuel related
Posted: Wed Jun 11, 2025 7:34 pm
Hi there,
I'm the proud owner of two Audi D2s — a front-wheel-drive 1999 A8 2.8 and a 2000 S8 4.2 quattro.
On to the issue:
I picked up the S8 back in 2023 for £650 as a non-runner. The fuel pump had failed, so I replaced it, added some fresh fuel, and she fired right up. Got her home and began the long road to recommissioning. Progress has been slow, mostly because I’m committed to using good-quality parts — but at 25, I don’t exactly have an unlimited budget. Also, my 2.8 seems to think my wallet is a bottomless pit
.
Fast forward to April: I started the S8, and it spluttered and died. After a bit of troubleshooting, I found it wasn’t getting fuel again. Here’s where I’m stuck:
At the terminal on the end of the fuel pump carrier (next to the relay), I'm only getting 3.5V — same at the pump.
I replaced the relay with a known good one — no change.
Pin 30 at the relay socket reads a solid 12V.
When I bridge pin 30 to pin 87, I get 12V at the pump.
This makes me think the wiring from the relay to the pump is fine, and the issue lies in whatever triggers the relay — but I’m not the best when it comes to auto electrics.
Any help, advice, or wiring diagrams appreciated. Just want to get the beast back on the road properly!
I'm the proud owner of two Audi D2s — a front-wheel-drive 1999 A8 2.8 and a 2000 S8 4.2 quattro.
On to the issue:
I picked up the S8 back in 2023 for £650 as a non-runner. The fuel pump had failed, so I replaced it, added some fresh fuel, and she fired right up. Got her home and began the long road to recommissioning. Progress has been slow, mostly because I’m committed to using good-quality parts — but at 25, I don’t exactly have an unlimited budget. Also, my 2.8 seems to think my wallet is a bottomless pit
.Fast forward to April: I started the S8, and it spluttered and died. After a bit of troubleshooting, I found it wasn’t getting fuel again. Here’s where I’m stuck:
At the terminal on the end of the fuel pump carrier (next to the relay), I'm only getting 3.5V — same at the pump.
I replaced the relay with a known good one — no change.
Pin 30 at the relay socket reads a solid 12V.
When I bridge pin 30 to pin 87, I get 12V at the pump.
This makes me think the wiring from the relay to the pump is fine, and the issue lies in whatever triggers the relay — but I’m not the best when it comes to auto electrics.
Any help, advice, or wiring diagrams appreciated. Just want to get the beast back on the road properly!