Crazjtk
12-27-2019, 12:52 PM
IÂ’ll try to keep this as factual and concise, with as much useful info as possible.
The carÂ’s a 2007 2.0t quattro. It has a K04 turbo with supporting mods (injectors, hpfp, exhaust) and APR tune.
When the car runs, it runs great. The problem is that it sometimes won’t start. It’s not very frequent, and I cannot reliably reproduce the problem, but it does not seem to matter what state the car is in (warmed up, cold, etc). Normally when I open the driver’s door or turn the ignition to “on” I can hear the LPFP priming the system, but if I don’t, that generally means the car is not going to start. I have not experienced a failure to start when the car is still fully warmed up or a very brief (~5 minutes) off-time, but I HAVE experienced it after being off for only 20 minutes. On all of the short-break failures to start, the car started running for a moment, but then died when it had used up all the fuel still in the line. The car has never died while fully running, only on those startups.
If I pull my key out and wait for a few minutes, the fuel pump will prime and the car will start like nothing was wrong.
So far I have replaced the LPFP, the fuel pump and ECU relays, and had rebuilt the HPFP previously. IÂ’ve checked the replacement relay and fuses. The only other problem I have with the car at present is a very rare CEL for a low voltage OBDII code.
My only ideas for causes at present are a coolant temp sensor, as others on the forum have experienced, or battery problems. My reasoning for battery being that when I bench-tested the fuel pump relay, it required a full 12v to close, so perhaps a sketchy battery could cause a slight undercharge (which might cause my CEL too)
I would appreciate any input or advice, this little gremlin has been driving me nuts and making my father say some pretty unkind things about my beloved Audi.
The carÂ’s a 2007 2.0t quattro. It has a K04 turbo with supporting mods (injectors, hpfp, exhaust) and APR tune.
When the car runs, it runs great. The problem is that it sometimes won’t start. It’s not very frequent, and I cannot reliably reproduce the problem, but it does not seem to matter what state the car is in (warmed up, cold, etc). Normally when I open the driver’s door or turn the ignition to “on” I can hear the LPFP priming the system, but if I don’t, that generally means the car is not going to start. I have not experienced a failure to start when the car is still fully warmed up or a very brief (~5 minutes) off-time, but I HAVE experienced it after being off for only 20 minutes. On all of the short-break failures to start, the car started running for a moment, but then died when it had used up all the fuel still in the line. The car has never died while fully running, only on those startups.
If I pull my key out and wait for a few minutes, the fuel pump will prime and the car will start like nothing was wrong.
So far I have replaced the LPFP, the fuel pump and ECU relays, and had rebuilt the HPFP previously. IÂ’ve checked the replacement relay and fuses. The only other problem I have with the car at present is a very rare CEL for a low voltage OBDII code.
My only ideas for causes at present are a coolant temp sensor, as others on the forum have experienced, or battery problems. My reasoning for battery being that when I bench-tested the fuel pump relay, it required a full 12v to close, so perhaps a sketchy battery could cause a slight undercharge (which might cause my CEL too)
I would appreciate any input or advice, this little gremlin has been driving me nuts and making my father say some pretty unkind things about my beloved Audi.