Audi A6 2.5TDI 2000reg intermittent start problem

[Khi]

Hi,

I'm a newbie to this forum, but I'd really appreciate any advice 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 as to possible causes, including:
- Faulty coolant temperature sensor
- Faulty fuel pump (although why would it run fine sometimes but not others?)
- Air leaks in the pipes
- Faulty immobiliser

The car doesn't go in to the garage until the 6th July, so anything you guys could suggest beofre then 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.

Cheers guys

[NickPicks]

I'd say the first thing to do is to get a fault code read.

The double sided fuel tank, I thought was only for the Quattro versions.

How much white smoke? Is it smoke or steam? What's happening with the water in the cooling system?

Also, let us all know what engine code it is (sticker in service book or spare wheel well)

[Khi]

I'd say the first thing to do is to get a fault code read.

The double sided fuel tank, I thought was only for the Quattro versions.

How much white smoke? Is it smoke or steam? What's happening with the water in the cooling system?

Also, let us all know what engine code it is (sticker in service book or spare wheel well)

Thanks for taking the time to reply Nick.

You're probably right about the dual sided tank being on the Quattro - our mechanic at the garage was suggesting that over the phone, just from his memory of that model of car.

I couldn't say if it was smoke or steam to be honest, I'll probably need to run it again to check - I'll do the same and monitor the coolant, while it's running. Will get engine code - all of this I'll need to do when I get home this evening. Are you thinking it could be the head gasket? I did check the oil repeatedly and haven't found any white blobs (water ingress), however the level does seem fairly high - unable to say whether that's because it was overfilled or not.

Unfortunately I don't have any VAGCOM software or hardware, and I fear that taking it to the local Audi dealer will probably require me remortgaging the flat. I do have a mate who races cars professionally so maybe he knows someone with a cable and the software, I'll drop him a line.

Thanks again

[Peter D]

After a fail to start, when it does start does it start up normally or chug, chup, splutter in to life.
Can you hear the lifter pump in the tank run for 2 seconds when you turn the ignition on.
Try the secong ignition key. It could be the coolant temp sensor lying to the ECU. Regards Peter

[Khi]

After a fail to start, when it does start does it start up normally or chug, chup, splutter in to life.
Can you hear the lifter pump in the tank run for 2 seconds when you turn the ignition on.
Try the secong ignition key. It could be the coolant temp sensor lying to the ECU. Regards Peter

Hey Peter,

When it does finally fire up it seems to start pretty promptly, no stuttering or chugging. It takes a lot of turning over before it does start though. I still haven't yet ascertained a clear pattern as to when it does or doesn't.

I can just about hear something when the ignition is turned on, (while I'm waiting for the coils to heat). I also see on the voltmeter on the dash that there's a load on the battery for a few seconds (lasting longer than the coils heating), once I see the needle jump up a volt or so then that's when I try to start it. Maybe it's the lifter pump imposing the load on the battery?

Unfortunately I only have one key - yet another sign that in hindsight I should have avoided the purchase of that car with a barge pole!

I'm more and more tempted to replace the temperature sensor, since it's such a small item...

[Peter D]

As it start cleanly then I suspect a fuel/immobiliser.
We need the engine code like, ABF. It is either in the service book or in the spare wheel bay. Regards Peter

[Peter D]

If it was the temp sensor then it would not start cleanly as it would be overfueled during all the cranking. Regards Peter

[Peter D]

Do you have a multi meter. Regards Peter

[NickPicks]

With the talk of engine coolant sensors, it hasn't got a "Tuning Box" installed has it? These are the cheap things from ebay which cause the ecu to think the engine is colder than it is, and overfuel. They're a cause of trouble.

[Khi]

Do you have a multi meter. Regards Peter

I haven't got one but I can get a hold of one.