SilverHotz

Car was running perfectly fine. Parked for about an hour, got back in and it wouldn't start. Checked fuel pump fuse, electrical connections...still cranking and no fire at all. Then I removed the gas cap and it started right up. Any ideas? I put the gas cap back in and it's still running fine and restarted with the gas cap in. I'm wondering if there's something wrong with the cap itself or the evap/purge valve.

2000 1.8T Quattro

David.Norton

Modern caps don't have a vent, I think you are on the right track with the evap system.

turbo510

Check the purge valve. If this is stuck open, fuel vapor will fill the intake manifold, causing the mixture to be too rich to light.

SilverHotz

I just left my house went about 1/4 mile and it stalled twice and then died. I cranked it about 10 times and banged the fuel tank with a wrench and was able to get it to start with some luck. I first took the fuel cap off to see if that would again fix it but it didn't - at least not immediately. Is fuel pump failure common at 115k / 12 years old on these B5s? How difficult is fuel pump replacement? I took a look at the bentley and it lists 2 VAG tools required which look like they actually might be required.

GTA_Driver

thebut the pump does fail. Mind you, I haven't yet replaced the fuel pump in any of my 2 audis, nor on the 1993 100 that's still in the extended family. And that one has over 360kms.

turbo510

The pumps do fail, I've changed mine twice (once because it was a crappy counterfeit). Special tools may be specified, but are not mandatory- basic tools will do the job. The only thing that I'd suggest is to have a pair of long rubber gloves, because your hand may be below the fuel level. Speaking of that, the job will be somewhat easier if the gas level is say 1/4 or less.

SilverHotz

Any advice on replacements? The genuine Audi replacement is pricy. I noticed a few aftermarket options from ECS that are far cheaper.

SilverHotz

I talked to a friend who is a mechanic and specializes in VWs and Audis. He said since it is intermittent it's more likely the fuel pump relay than the pump. Anyone have the fuel pump relay fail? That looks a lot easier to replace than the pump which would be nice.

turbo510

Step one in these type of cases is to change the $10 ignition switch.

Could be the relay, but then there are a number of things that could contribute to the car not starting; it doesn't seem like you have really confirmed that the pump is bad. As a side note, you can bypass the entire A4 electrical system and power that pump with a 12V motorcycle battery, to see if the pump always runs when an alternate source is supplied.

SilverHotz

What are you referring to by the $10 ignition switch? I did some more troubleshooting tonight and of course in the middle of troubleshooting the problem, it went away and the car started. I let it run for a while until it died again - maybe 10 minutes. I had the cover off the relay and I watched the relay open when it died which it's hard to tell the cause from the effect, but about 2 seconds after it died, the relay closed again for a second and I heard the pump prime. I was certain at this point it was the relay until I read your post about the ignition switch which I would presume could cause the same intermittent sort of behavior? Can you explain a little more?