hanilanzi

hi all,
have a 2000 A8 with 130k that won't start, it turns but no start.

let's start here:
i changed the spark plugs 10 days ago and it worked fine that day,
next day wife calls me and says it won't start, she has been driving it earlier, so the car started when cold, but won't when warmed up.

so i went back to what i did last (spark plugs change), i ordered new 8x Bosch Platinum 4+ and put those in, nothing changed, car still won't start when warm, and not, sometimes when cold!

i started looking into fuel distribution and replaced the fuel filter.

car started right away, but then when warmed up, no start again!

i opened up the back cover in the trunk where the fuel pump is.

i've noticed that sometimes when i do a contact, i can hear the fuel pump spin for couple seconds and then when trying to start the car it kicks in, car starts and it is working.

I've been tested this about 10 times and sometimes the pump spins and sometimes it doesn't when trying to start.

i looked at the fuel pump relay (372) and it seems like it clicks,
i even opened the cover off of the relay and while contract is on i would tap on the relay and i could hear the pump kick in when holding
it down,
however when trying to start the car sometimes the pump kicks in and sometimes it doesn't.

i was reading some other forums and some people are suggesting there is a crank sensor of some sort that might be bad and when trying to start the car it does not send the signal to the relay to start the pump.

could that be it, or is my pump dying?

any help would be greatly appreciated.

thank you,

Hani

spitanddirt

It's a pretty safe bet that your fuel pump has failed. If both your fuel filter and fuel pump are original, your fuel pump has probably died early. Here's a link to my fuel pump thread. Change in yourself for about 1/3rd the cost. Don't buy the entire assembly, just buy the pump like the rest of us. Just remember, you can NOT buy the right pump at any auto parts store, you need to source it from Europe as I did.

https://www.audiworld.com/forums/sho...uel+pump+fails

silverd2

If you want to be sure that all parts of the circuit are working properly (ingnition switch, crank sensor, fuel pump relay, etc...) and narrow it down to the pump, you need to hook a volt meter to the pump electrical leads (at the pump) and watch for 12v during starter operation.

There should be full battery voltage at the pump every attempt, whether the pump runs or not. Voltage will stop when the engine is not turning...the crank sensor will cut ground to the relay when no engine turn is detected.

hanilanzi

There is a connector on top of the assembly of the fuel pump in the trunk that has four wires all different color. Do you
Know which two wires should have 12v on it when contact is made ?
Thank you.

silverd2

Yep, it's the thicker 2 wires (2.5mm)...green w/red stripe is 12v to the pump and solid brown is ground for the pump.

The small wires (.5mm) are for the level sensor...brown w/violet stripe and brown w/yellow stripe.

hanilanzi

thank you, i will test this today.

moe1355

Thank you for the info, I am in the same situation, and was wondering which wire is which, great post, thank you!
My car is a 2000 audi A8 4.2l as well it cranks but does not start, so with the +/- wires you described above I can simply hook the + to the car battery’s + and the negative with the negative to determine if the fuel pump is working or not right?

Where are the crank sensor and the fuel relay located?
I already found the fuel pump fuse, that one is ok.

Thank you for getting back to me.

omarcarbomb

https://www.audiworld.com/forums/a8-...n-etc-1751534/