77scottaa

Well, My 2001 A8 fuel pump works great with 12 volts. It is only getting 8 though. 8 volts at the fuse and 8 volts at the relay ( if I got the right relay) that is. WHAT WOULD DROP THE VOLTAGE all of a sudden. It died on my wife. Is the the relay or maybe something with the immobilizer? I am stuck. When I put 12 volts to the pump everything is fine. Can U buy just the large rubber seal for the fuel pump? I removed and replaced it. Couldn't shrink it enough to fit back together as new. Any suggestions? I cut out a piece and glued it back together ( after boiling out the gas from the seal)

TonyA8

You need to do some debugging...When you see 8 volts, measure at the battery, before the relay, after the relay, before and after the fuse, and at the pump. Where-ever you see the biggest drop in voltage, that is where you have the problem.

It could most likely be a bad connector, relay, or fuse. This of course is assuming that the fuel pump is not taking more current than it should.

Sometimes just disconnecting and reconnecting a connector will clean the contacts and all is fine. If you find that, take the time to clean those connectors.

SCL

I'm not sure if the 2001 is the same or not...
The '98 provides voltage for one second when the key is first turned on, then voltage again while the starter is turning -- But, the voltage is less while the starter is drawing current. First it shows about 11.75 V, then about 10.25 while the starter is turning...then jumps up to something higher after the engine starts and the alternator kicks in.

Here are some pics of how I checked the voltage. I used a male disconnect blade connector to plug into the top side of the fuel pump fuse holder, and found a good ground on that small threaded pin that where the cover is fastened. The first one was taken right when the key is first turned on. The second pic is while the starter is turning.

Also, you can check the current. One way is to add a piece of wire with known resistance and check the voltage drop across it. I wired directly to the fuel pump, and added and extra 10 feet of 20 gauge wire which has a resistance of ~.1 ohms -- and plugged into the top of the fuse holder. I saw almost 2 volts. Divided by .1 ohms gave me 20 amps. (which actually also means that the fuel pump was only getting 8-10 volts, but the car did start and did run). That explained (in my case) why the fuses kept popping. I was lucky though -- It cleared itself out and now is working fine on the regular circuit. I am guessing it was clogged or something.

I didn't check the relay...so I didn't get into that procedure. It's possible that the relay has a bad contact and is not only robbing some voltage but is limiting the current. You could take out the relay, and apply voltage to close the contacts, and see if there is resistance across the contacts. It should be zero.

Something there should reveal a clue. Hope some of this helps... Post some results afterwards.

<img src="http://pictureposter.audiworld.com/100685/dsc04882-1.jpg">

<img src="http://pictureposter.audiworld.com/100685/dsc04885-1.jpg">

77scottaa

Thanks for the tips. I will try to get debugged in near future.I must go out of town again. I have the same voltage at the fuse, pump, and relay. I hooked 12 to pump so my wife could get around. Runs great for now. 2001 pearl blk with tan and chocolate interior.
I will post further updates.