Audi A6 Estate 2.5TDI 2000reg intermittent start problems
I'm a noob to this forum, but I'd really appreciate any adive or help you knowledgeable people could give me.
I've recently bought a 2000 reg Audi A6 estate, and it's pretty obviously I've been done by the last owner. I'll try to describe the syptoms as best I can.
When I met them to buy it, the engine was running, so I turned it off to let it cool for a bit. Started and stopped it while I inspected the vehicle but could find nothing too untoward. I then drove 5 hours from Wales back to Brighton with no issue (I once stopped and turned the engine off to refuel at a fuel station).
We drove it on and off the next couple of days with no issue, then suddenly one morning it wouldn't start. It turned over repeatedly, however wouldn't fire. The battery eventually ran pretty low so I had to stop trying. A few days later we hookep up the jump leads to a mates car, and it turned over for aaages, then suddenly fired! I turned it off, then started it again no worries. I waited till late that night to go out and start it once more, and again it started no problem. A couple days later we drove it around, put loads of diesel in it, filled the screen wash etc, then parked it again. The next day, once again it wouldn't start.
It is booked to go into the garage, but I'm trying to think of everything I could to help the guy find the fault.
There is a clear line that connects to the pipe from the tank, and is before the fuel filter, this showed occasional bubbles going through it, which made me think there was an air leak in the pipes coming from the tank. I looked all over the pipes but couldn't find any diesel weeping out of any joints. I filled the car with diesel, and the bubbles appeared to stop, which made me think maybe it was something in the tank causing bubbles (apparently the tank is split into two, and a small pump balances the levels in the two tanks, sometimes an issue with this pump can cause the side that feeds the engine to run dry). However the day after filling the tank is when it wouldn't start for the second time.
Other factors include:
- There is white smoke coming from the exhaust when it does run, I don't know if diesels are the same, but it makes me think it's running lean (again fuel supply issue?).
- There is a high pitched whine coming from the engine when driving around - I can't figure out if that's just the turbo or something else
- There doesn't appear to be any power issues when driving, it seems pretty pokey and drives ok when it's going
- On the two occasions it refused to start, it happened when starting from cold (ableit it's mid summer at the moment). The first time it ticked over for a couple of seconds, then shuddered and stopped. The next time it was ticking over for a while, while I faffed around with seatbelt etc, then when I went to pull away it stopped
- Both times it failed to start the car was facing uphill - although it did start on other occasions in the same spot
- I have a receipt from the last owner saying the fuel pipes, fuel filters and oil filter were recently changed (makes me think they were trying to eliminate air leaks)
Reading all around the forums etc I've found many suggestions, including
- Faulty coolant temperature sensor
- Faulty fuel pump (although why would it run fine sometimes but not others?)
- Air leaks in the pipes
The car doesn't go in to the garage until the 6th July, so anything you guys could suggest would really be appreciated.
I've obviously been royally done over by the last owner. :(
Thanks in advance for taking the time to read this! Any other info I can give I'm happy to crawl around the car/engine and find out for you if it helps you to diagnose.