laychooba

hahahaha the party isn't stopping with my A8. i guess bad things
come in threes.

vehicle: 2005 A8L

before i brought it in the other day to do the timing
belt (which is done now) the car died on me just as i
was rolling out of work. started it up again, ran for like 30
seconds, then died. tried again, same thing. i limped it back
to work and stashed it there for the night.

next day we bring it in, do the timing belt which went rather
smoothly i could say. go to start after the job, same thing. 30 seconds then
dies.

checked everything and more or less narrowed it down to fuel
pump or fuel pump relay. while it was running on the lift, i could
hear a pump, which on the drivers side click off after it was started
for 30 seconds, then the car would die. so i see a few people here have
had a similar problem with a dead pump.

what we did try was taking out the fuel pump relay in the trunk, we made
a jumper wire between 30 and 87 on the relay, started up the car and it
ran what seemed to be fine and didn't stall.

thing is we then tested the relay and it seemed to be doing it's job. there was
power flowing through the main terminals with the 85 and 86 12v'd and neg



so either could be relay, pump or wiring. what are some of your takes on this?
gonna dive in tomorrow, just rather not have to take more of the car apart than i have to. ha

thanks!

dvs_dave

As the fuel tank straddles the propshaft, it effectively has two halves. So to ensure even fuel draw and distribution there is a pump in each half.

The primary pump runs all the time, and the secondary pump kicks in during engine startup, high engine loads, and probably a few other circumstances as the ECU sees fit.

Sounds like the primary pump is not working which is why the engine dies after 30s. The secondary pump runs for 30s after startup supplying enough fuel pressure for the engine to run, but then it shuts down. Normally the primary pump would continue to run but for some reason it's not. Do the usual checks on that pump to check its function and go from there.

MP4.2+6.0

+1

laychooba

yeah it was the right side fuel pump.

man, i can't catch a break. it was not that fun to change with the tank
FULL to the brim, but wasn't so bad. what's another $300 on top of my
timing belt parts? lol

mishar

It's not cheap, but it is closer and closer to the original value (100K) for the fraction of it.