Audi v8 troubleshooting

[Grillage]

Hey guys, i picked up a cheap 93 V8 this weekend in non-running condition.

The PO claims he was driving to work and the car died. He'd had a CEL for a few days previous to this.

It has spark and I have established that it will turn over with starter fluid. I have no CEL or codes with VAG COM and the timing belt is intact.

I have also proven the fuel pump works and that the car doesn't start with the FP relay jumpered.

So I guess what it comes down to is the injectors. They do have power but my understanding is that the pulsing is the ground connection right?

The big question is what would cause motronic to keep the injectors from firing?

There is another thread on this here for some background...
http://www.motorgeek.com/viewtopic.php?f=5&t=54444

[scubadave]

sounds like cam sensors.

[Grillage]

sounds like cam sensors.

The only cam sensor is the G40 hall sensor inside the PS distributor. My understanding is that in failure it only retards timing rather than causing a no-start or the stall issue the PO reported.

[Grillage]

New development. I DO have injector voltage. Hooked a test light up to one of the injector harnesses and it blinks when the injector would be firing.
Tested fuel pump flow rate and I get about 100ml in 15 seconds. Bentley specs about 650 ml in the same time period.

So looks like way slow fuel delivery is the culprit. What I don't understand is why injectors won't spray at all. The fuel rail was full though with that low delivery I would imagine the pressure is also very weak.

[scubadave]

Of all my years as a tech, the neglect of regular maintenance (specifically the fuel filter) was 98% the reason something went wrong. Regular people just don't think about maintaining their car as a necessity but more of a nuisance. As I have maintained many members of my family's cars, I can use my fathers camary as an example. 450,000 miles and I have never replaced the fuel pump.

I would wager the fuel filter was neglected till the last minute, if replaced at all, and severely damaged the pump. its the usual reason the pump has to be replaced at all. At least that's all you have to do to fix it. I hope the tank isn't full. Immersing your arm in fuel is not at all fun, nor at those temps. good luck!

[Grillage]

Of all my years as a tech, the neglect of regular maintenance (specifically the fuel filter) was 98% the reason something went wrong. Regular people just don't think about maintaining their car as a necessity but more of a nuisance. As I have maintained many members of my family's cars, I can use my fathers camary as an example. 450,000 miles and I have never replaced the fuel pump.

I would wager the fuel filter was neglected till the last minute, if replaced at all, and severely damaged the pump. its the usual reason the pump has to be replaced at all. At least that's all you have to do to fix it. I hope the tank isn't full. Immersing your arm in fuel is not at all fun, nor at those temps. good luck!

I think you're right. I got the filter off a couple days ago and it looks like it has never been changed - or at least not for a long time. As for the gas tank, it was about half full, I went out and bought two more 5 gallon gas cans and drained it to about a quarter inch. much easier to deal with now. Also, I need to replace the pump in my S6 still and now I'll have a little training!

[scubadave]

yeah. if you havnt thrown the filter away yet, try blowing through it with your mouth and you will see how the pump was treated.

[Grillage]

Right you were scubadave!

Fuel filter had virtually no airflow


I did replace the pump too and the car started right up!
Hoorah!

[scubadave]

Nice