Zumkopf

Finally got my 98 D2 Q sorted, even cleaned the cowl drains (they weren’t bad) and washed/waxed it. Everything was fine with it for several days. Thursday I took it out, weather clear and dry, and after ten minutes running flawlessly, it died while I was stopped at a light. Cranked fine, wouldn’t catch, wouldn’t even cough. Called AAA, they flatbedded it to a shop. Friday morning the shop called, said it started right up. No codes stored. They even idled it for half an hour to make sure it was ok. So at lunchtime I went to pick it up. No charge! I go outside to drive it home, get in, you guessed it, it cranked fine but wouldn’t start. Not for me, not for the tech. Still no codes.

I replaced the fuel pump successfully a few months ago. I can hear the relay click when I turn the key. Not sure what else could be intermittent and yet leave no codes. Maybe warming the car up had something to do with it? Thoughts?

Z
1998 Audi A8Q D2 144k

jfrahm

Be ready to troubleshoot if it happens again.
Is the tach rising up when you crank it?
If so, spray some starting fluid (easy to do into a vacuum line) does it catch? Don't bother if there is no tach signal as there won't be fuel or spark either.

Has it been run low on gas after the fuel pump job? If it poops out when low on gas but starts and runs OK when a small amount of fuel is added then the scavenging system might not be working.
If so it'll only run a few blocks on the pint of gas that gets to the fuel cup when gas is sloshed in, and then poop out again.

rbjones17

I had this happen as well after replacing fuel pump. You must be very precise and actually use a remote camera to ensure that the top tube mounts with the bottom tube. If you don't mate the two tubes together then the car will just die after it reaches half tank. It took me several weeks and some troubleshooting to figure this out. To confirm this hypothesis, add several gallons of gas or fill it again. If it runs, then you'll need to go back through the tedious procedure of mating the top of the fuel pump to the bottom pick up line.

Zumkopf

RBJ, I thought of that, but if the tech was telling the truth about it starting and running for him, I think the scavenge tube mismate theory is unlikely. I don’t have a remote camera either. But they probably do at the shop, so I’ll suggest it to them if they remain flummoxed. [Or, couldn’t you just check for fuel pressure during crank/no start? If it”s supplying fuel, the problem is likely electrical.]

rbjones17

Sure, you could check fuel pressure. That is what that you should do. This fuel pump is very particular with its fuel scavenging venturi system. I ran across what appears to be identical circumstances 6 months ago. I had to replace the pump 4 times before I ran the remote camera (it was a hundred dollars) and actually watched the upper tube mate with the lower tube. It kept throwing misfire codes and I replaced coil packs spark plug wires, spark plugs, etc. until I went back and actually watched the tubes being mated and was then able to run the tank down to dry with no misfires and no problems since. Good luck.

rbjones17

Maybe these pics will be of assistance.

rbjones17

The pipe labeled number 1 on the next to last pic is the critical one to mount correctly.

Zumkopf

RBJ, thank you -- sincerely! -- for the fuel pump material. I will without doubt find it useful in the future, and so will anyone who owns a D2, sooner or later.

But new developments. I went over to the shop garage with an extra key. The car started instantly. I ran it for about ten minutes after it reached operating temperature, and it ran fine without a hiccup. I then shut it down, figuring I was back to square one. But on a lark, I tried to restart it. This time, crank crank crank but no start. And the tach needle never budged from its bump stop.

So where do I look now? What problem could develop in the (ignition?) system where it connects fine when cold but not when it's hot?

Thanks in advance, Z
1998 Audi A8Q 144k

rbjones17

Only other time that I had an gremlin crank no start was after that I had performed the timing belt procedure and there was a loose connection to the CPS just in front of the driver behind the firewall. When I would shake the wire with the ignition on, I could hear the fuel pump engaging and then disengaging due to the loose wire.

I also purchased a spark plug light bulb tool when I had my fuel pump problem and I verified that every spark plug was hot.

If each spark plug is lighting up and the car isn't running and has no codes, I'd go back to the fuel pump.

Cheers

Rich

rbjones17

These were the pictures that I took that ensured that my fuel pump was reconnected properly. In the absence of this picture, there is always the potential that it was mated improperly. If this happens, the car will start and run after the filler cup has been filled, without regard to the fuel level in the tank. After the cup is emptied, the fuel pump will be starved for fuel unless the tank is over half way. Alternatively it will suck air and then fuel as the fuel is josteled in the tank.