I think i need a new fuel pump for my Audi 100 '89. The one that i have now is 50k miles old.
The car lost power today twice when i was on highway ramps. The second time i heard a constant noise from the rear of the car, the car lost power, almost died and it was shaking a little. I pulled on the side, turned off the engine and started it again - no noise and the car was running fine until i got home. The level of the fuel in the tank was low - no more than 4 galons total with the reserve but it has never happened before even when my "gas warning" light has been ON. I also had the quiet "hummmmming noise" for the last 5-6 months on and off. Is it time for new fuel pump??? What about fuel pump relay?
Also, are there any different sizes fuel pumps for this model? I saw at bimmerparts.com Audi 100 fuel pumps with 60 mm and 44 mm specification. (two kinds)Which one should i pick for my car or they would both fit? How to find out which one i need?

Thank you very much for your help!

This happened once to me. I was near empty and going up a hill when I started sputtering and hearing the same noise from the fuel pump. I think you were just running out of gas. I believe your fuel pump is in your gas tank like mine (86 5000 QT) so you have to keep a good level of gas in there. Just don't let it get near empty and you should be OK. However, please don't call me every name in the book if your fuel pump fails on your next trip ;-).

Every German fuel pump I've ever come across has hummed. I was taught that was how you knew it was working.

How many miles are on your car? Have you changed the fuel filters yet? It has been in my experience that 100,000 miles is not at all unresonable for a fuel pump life span. I'm sure that some of the others on this site could report similar experiences.

Start your car, and while it is running, head back to the rear of the car and listen for the pump. It should make a fairly constant whine or hum. If not, shut off the car, crawl underneath and start checking electrical grounds and other connections. This has been a problem I've had in the past.

Start cheap and work expensive - Check elec. connections, then change the filters, then the pump.

Good luck,
Erik

'90 V8Q
'87.5 GT

Thanks for the advice people. Now i also think that the reason for the trouble was the gas in the tank. It was too low i guess. Today the car runs fine. I have half tank of gas and there is no humming at all or hesitation.
The fuel filter is only 5k miles old. It should be OK. The pump that i have in the car has about 50k miles on it. It's my second pump. The car has about 130k miles.
I've heard before that sometimes "new" fuel pumps go bad after only 10k miles and i was afraid that it happened to me last night.
I wait a little more, drive around and observe if the problem will happen again. I may save $250 if i'm lucky this time. :)