Like an Indiana Jones movie I need the top guys on this one.......
I have a '96 Audi A4 Quattro 2.8 that was run over a parking lot barrier- ripping off the lower oil pan. I replaced the lower, upper oil pans, the radiator, the sway bar support on the passenger side, the fuel relay, the fuel pump and the fuel filter (it was still the original at 137k) and the car wouldn't start. I can run a 12v jumper to 2 of the posts on the catch (the fuel pump lid) and the car will start right up and run, but if I plug in the 4 prong plug it just sits and cranks. I have tested the two posts I jumped while they are plugged in and they show 12v when the key is turned (and you can hear the fuel pump kick on) and when you turn the engine over it shows 12v as well. The other two posts on that plug show nothing. What am I missing? I know the car will run but I am at a dead end for my ability to diagnose and get the last step.

 

Until the top guys show up, I'll weigh in...


So I think we can assume that the oil pan repairs, etc, are not involved in the engine not starting. Question: what do you mean running a 12V jumper to 2 of the posts? On the fuel pump connector, there are four terminals. The larger two wire are for the pump, the smaller two for the fuel level sender. Large green/yellow (I think) is +12V, the large brown should be grounded through the harness connector. I'd suggest that you plug that back on and return to your fuel pump relay. Remove the plastic cover so you can push the contacts together. The pump should run as long as you hold the contacts closed. Now when attempting to start, the contacts should close automatically when turning the key to Start. If on the other hand the pump does not run when closing the contacts, use a Voltmeter to check that you have battery voltage at all times on one of the relay's contacts. If not, check the fuel pump fuse.

 

OK I used a battery charger and attached alligator clip to the two terminals that run the fuel pump, so the plug to the front was not plugged in- and the car started right up. The pump of course ran continuous during that time but the fuel level sender was not powered because there was nothing attached to those terminals. So the car will start right off and run - it sounds great too- if I power the pump, but not when the plug is plugged onto the terminals. The fuel pump engages (runs) when the key is first turned on and shuts off after a couple seconds and then turns back on when the starter engages. When I attached the tester the wires to the fuel pump showed 12v both when the key was turned on and when the starter was engaged- the other two don't show any power as far as I could test. Although I can hear the pump turn on when the plug is attached no fuel comes out through the fuel filter- which means although I can hear it running it is not pumping fuel. My initial thought was that the mechanic reversed the wires on the fuel pump but you can feel air pressure pushing out of the fuel filter. So while I'm still vexed it seems like it is something to do with the plug and/or wiring of the plug. The set of fuses behind the relay panel wouldn't have anything to do with any of this would it? The airbag didn't deploy when it was wrecked so I'm pretty sure no fuel shutoff was triggered, but what the heck do I know?

You said to return to the fuel relay- you mean I should focus on that as being the problem possibly? I don't quite understand what you mean by saying take of the cap off and push together the contacts together- can you explain that a little more?
Thank you for your reply Turbo510- hopefully this information leads to more replies and or possible solutions.

 

I have been working on this or paying someone for repairs since August- I'm tired of paying insurance on this car so it can sit in the garage when I could be driving it....

 

The '96 is really a nice machine when you get those issues solved. I just sold mine, miss it already, but my wife put her foot down on two A4's (I have a 2005 3.0). So you can hear the pump run but no fuel? I'd check the hose from the pump to the white plastic cover, to see if it has come loose or there is a break. You should have fuel pressure immediately when the pump is running.

 

Does anyone have a wiring diagram that shows where the plug wires run along the bottom or inside of the car so I can trace them back to the relay panel? I want to rule out a damaged or almost broken wire from point a to point b. If my understanding is correct an 'almost' broken or damaged wire will still read 12 volts, but may not be able to have the correct amperage available when the fuel pump and fuel level sender come on. First off is this plausible? I know the fuel pump will run correctly and the car will start and run if supplied a full 12v connection (I used a 12v battery charger to confirm this by powering the terminals on the catch) and while I show 12v when the key is turned and also when the starter is engaged this doesn't mean that the right amperage is available for the pump and fuel level sender through that connection. Does that sound even remotely like I am on the right track?

 

The only thing I can imagine is going on is a bad ground wire from the fuel pump. since you appear to have 12V at the fuel pump connector, and the pump will run and produce fuel flow when you connect 12V and ground directly to the pump terminals, but will run (or sound like its running) and not produce any fuel flow when connected to the car, its one of two things outside physically damaged wires). Burned contacts on the fuel pump relay showing 12V but not allowing enough current thru to make the pump spin, or a bad ground wire or connection (high resistance) not allowing enough current to flow to spin the pump. I know the hot wire to the pump is a green/yellow wire, and it goes from the fuel pump relay to fuse 28, and then on to the pump. Fuel sender wires are violet/black from the instrument panel, and brown to ground. I'm assuming the fuel pump relay is black and its the same size as the green/yellow hot lead going to the pump. I would try to strip off a piece of the pump ground wire insulation as close to the connector as I could and attach a length of wire and attach it to a good ground point on the body of the car, to see if that will allow the pump to run properly.

 

So it looks like I'm going to have to trace that whole line from the relay to the pump to find out what is wrong. I was really hoping that was not going to be the case.

 

It's hard enough to find wiring diagrams for these cars, let alone find a routing drawing, or something showing where the various connectors are located. But I would assume the wires run under the drivers side door sill, and then across the area under the back seat. I know they are not under the car (or don't remember seeing them under there on my son's 96), so they shouldn't have been screwed up when the PO hit whatever he hit to knock the oil pan off. Clip an extra ground onto it and see if it will start. Can't have enough grounds on car circuits.