ghemmings Posted January 12, 2008 Report Share Posted January 12, 2008 Anyone know how to remove my fuel pump? I have removed the cover plate inside the boot (after a long fiddle removing the LPG tank!), but I'm left with what seems like a black plastic screw-off ring and a white plastic small round cover. Is there anything I should be careful with, or is it simply a pull out and replace job. Any ideas? Thanks in advance. Link to comment Share on other sites More sharing options...
Ska Posted January 12, 2008 Report Share Posted January 12, 2008 some info here: audipages Link to comment Share on other sites More sharing options...
PaulW Posted January 13, 2008 Report Share Posted January 13, 2008 Don't try replacing the fuel pump without the procedure and the new one on hand. It's an entire assembly that comes out of the tank, and has special suction lines. It actually works like a jet pump, and has cross connects between the tanks. Why do you need to replace the fuel pump? Link to comment Share on other sites More sharing options...
Figure11 Posted January 13, 2008 Report Share Posted January 13, 2008 The graphic from Elsawin if it's any help. Mike Link to comment Share on other sites More sharing options...
ghemmings Posted January 13, 2008 Author Report Share Posted January 13, 2008 [ QUOTE ] Don't try replacing the fuel pump without the procedure and the new one on hand. It's an entire assembly that comes out of the tank, and has special suction lines. It actually works like a jet pump, and has cross connects between the tanks. Why do you need to replace the fuel pump? [/ QUOTE ] I need to replace the fuel pump because the fuse keeps blowing. If I put a 15A fuse in the pump runs for about 2 seconds, then the fuse blows (just enough to prime the fuel rail and start the engine for a second). If I put a 25A fuse in (just for testing) the pump runs for about 6 seconds then the fuse blows. Do you think it might not be the pump? Link to comment Share on other sites More sharing options...
PaulW Posted January 13, 2008 Report Share Posted January 13, 2008 You have to troubleshoot it first.....there is a connection at the trunk (link to the audipages article above), disconnect it there and take resistance measurements to ground on the tank side connector. There is a brown wire (earth) and another colored wire which is the power. Go from the colored wire to ground with a ohm meter and see what resistance you get. Do this again on the colored wire on the wiring harness side to ground with the ignition off. You should have greater than 1,000 ohms on the wiring side and an open circuit on the fuel pump side. Then ground out (earth) the fuel pump side brown wire, and once again take a resistance measurement to ground from the colored wire side. You will find a low ground reading somewhere which is causing your problem. I would say it's most likely NOT your fuel pump. Link to comment Share on other sites More sharing options...
ghemmings Posted January 13, 2008 Author Report Share Posted January 13, 2008 Thanks for the procedure PaulW, I'll try it at the weekend before buying a new pump. I disconnected the pump connector and put a new fuse in and it did not blow with the ignition on, hence it doesn't seem like a wiring fault to me, but I hope you are right! Link to comment Share on other sites More sharing options...
PaulW Posted January 14, 2008 Report Share Posted January 14, 2008 So if the fuse didn't blow with the connector disconnected, you either have a fault on the postive (power) side from the power supply going up to the connector....but this fault is not enough to cause the fuse to blow.....or it's in the wiring or pump from the connector in the trunk. It's either: 1. The fuel pump has problems and is either drawing too much current due to a mechanical load or electrical fault. 2. There is an electrical fault that is on the same circuit upstream of the fuel pump and is adding to the current draw on the pump circuit. When the fuel pump and the fault are combined, they are in excess of the fuse rating and blow. So with the electrical connector disconnected from the pump, go from the power wire to ground and take a resistance measurement. It should be much more than 1000 Ohms. Take a resistance reading across the fuel pump from the power connector to the ground connector. The Bently manual states that a good fuel pump should draw 8 amps and with the tank dry, it should draw 4 amps. So that's 1.5 ohms for 8 amps and 3 ohms for 4 amps, so the pump shouldn't be reading less than about 1.5 ohms....but it's a motor....so it's not going to be exactly that. See what that does for you. Do you have the fuel pump replacement procedure? Do you know that they are about $900 in the U.S.? I would hate to know what they cost in the UK. Link to comment Share on other sites More sharing options...
PaulW Posted January 14, 2008 Report Share Posted January 14, 2008 So I just looked at the wiring diagram and the only thing on fuse ST4, S1 (fourth row down, first fuse, 15 amp) is the fuel pump. In this connector here: The brown is the fuel pump ground (earth) and the green and yellow is the fuel pump power. These are the two wires you need to test. They are the 2.5mm wires. The other two smaller wires are for the fuel tank level sensor. I would also inspect the connector itself once it is pulled off and make sure it's not heavily degraded. That could possibly lead to a leakage current also. Link to comment Share on other sites More sharing options...
PaulW Posted January 14, 2008 Report Share Posted January 14, 2008 I have two procedures I can forward you, your email is not part of your profile, tried to attach them twice, no dice. Send me an email. Link to comment Share on other sites More sharing options...
ghemmings Posted January 14, 2008 Author Report Share Posted January 14, 2008 Paul, thanks for all your time and effort helping me out, it's really appreciated. I have pm'd you my email address. Incidently, I spoke to Audi-Hereford stealers last week and a new pump is £192 including VAT. Link to comment Share on other sites More sharing options...
Ska Posted January 14, 2008 Report Share Posted January 14, 2008 Wow thats come down in price froma couple of years back; I was quoted around £500 from the stealers in Glocestershire Link to comment Share on other sites More sharing options...
ghemmings Posted January 14, 2008 Author Report Share Posted January 14, 2008 Yeah, that's what I thought. Some older posts reckon it was around the £500-600 mark for a pump. I've heard that Audi have dropped the cost of a lot of parts recently. I think it's worth getting prices off Audi for all parts before buying from aftermarket suppliers. Link to comment Share on other sites More sharing options...
PaulW Posted January 14, 2008 Report Share Posted January 14, 2008 When you get a fuel pump from the dealer, it's an entire assembly.....sounds like you are getting a price for just the pump and motor assembly. I have heard of people getting that in Europe, but in the US, you can only get the whole assembly with the plastic casing on it. Here is a previous post with all the wiring diagrams: http://forums.audiworld.com/a8/msgs/121337.phtml Here is a post with a picture of the assembly that comes with the fuel pump (see other pics in the thread): http://forums.audiworld.com/a8/msgs/110842.phtml Another post (by Sven, can you believe it?) on how it all works: http://forums.audiworld.com/a8/msgs/75866.phtml That should keep you busy for a while. Link to comment Share on other sites More sharing options...
ghemmings Posted January 27, 2008 Author Report Share Posted January 27, 2008 I have finally got round to fault finding the fuel pump. I removed the pump connector and measured the loom resistance on the car side. This was several hundred megohms. Then I tested the resistance on the pump side and this was 2.4 ohms which is within spec according to PaulW's advice. I then connected a new fuse and tested the car loom resistance. This was again several hundred megohms. I then truned the ignition on and started the engine. To my surprise it ran continuously and the fuse did not blow! I don't know what I have done, but the must have been a short on to ground on the loom or something, just as PaulW suggested. When I removed the connector, I pulled the loom out from around the pump housing to check for chafing or a short but cannot find anything. Maybe disturbing the loom has 'unshorted' the loom further inside the car. I will post again if the fault re-occurs. Thanks to everyone, especially Paul for all your help. Link to comment Share on other sites More sharing options...
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