Starting problem on Audi A6 2.5 TDI

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Sun 19 Dec 2004 14:44
Starting problem on Audi A6 2.5 TDI - Big Dave
I'm not sure if there is much experience of the VW/AUDI 2.5 V6 TDI (150bhp) engine amongst members, but can anyone give me some suggestions for the following cold starting issue:

I have a 1998 Audi A6 Avant 2.5 TDI with nearly 170,000 miles. Since buying the car with 137,000 miles, it has never been particularly good at starting from cold. Now its winter, it takes about 4 seconds of cranking to start firing. In the last second or so of cranking, I can hear that several of of the cylinders are firing, but it takes a bit more cranking to get the engine to start (which is sometimes followed by a cloud of white smoke from the exhaust). The engine also sounds a little bit lumpy until warm (after which it runs fine), so I am not convinced it runs properly on all cylinders during the warming up phase.

I recently replaced all 6 of the glow-plugs as a first stab at fixing it, but it only made a marginal difference to the car's starting performance. I nearly always use Shell branded Diesel and have also tried one of the 3rd party (Redex) fuel additives for cleaning the injectors.

Does anyone have an constructive suggestions as to what other things might be causing this problem?
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Sun 19 Dec 2004 15:41
Starting problem on Audi A6 2.5 TDI - adverse camber
Is your battery the correct spec and holding a decent charge ? And is it a decent brand ?

Have you checked for error codes ?

Id the temp sender working ok ?
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Sun 19 Dec 2004 19:08
Starting problem on Audi A6 2.5 TDI - Big Dave
The battery has plenty of charge and turns the engine over fine.

I presumeably need to find somewhere with a VAG-COM diagnostic unit to test the temp sender and look for error codes?
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Tue 21 Dec 2004 09:20
Starting problem on Audi A6 2.5 TDI - Durhamman
Yes, find a local Bosch outfit. I had similar problems with my Audi. They put in on their machine, did a road test, and within an hour problem diagnosed and sorted (a leaking hose, like a bicycle pump connector). £60. Perhaps lucky. Have heard stories of cars requiring lengthy diagnosis. But there you go. I avoided my main dealer like plague. They are not skilled up to deal with serious problems of this nature and would farm it out, quite likely to their favoured electrical outfit. Bosch are better as they supply Audi and have the specialist equipment. Horses for courses. Best of luck
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Tue 21 Dec 2004 09:28
Starting problem on Audi A6 2.5 TDI - Durhamman
I too have an Avant but 1995 172,000.
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Tue 21 Dec 2004 10:36
Starting problem on Audi A6 2.5 TDI - Roly93
Sometimes problems like this on highish mileage diesels are caused by tappet clearances being too small, causing initial loss of compression.

I'm not sure if the Audi engine is prone to this but its worth checking.

The only other common thing I can think of is a fuel system air leak, which would manifest itself in all temperatures, ie not just freezing cold morning starts.
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Tue 21 Dec 2004 10:45
Starting problem on Audi A6 2.5 TDI - P 2501
White smoke on start-up, this could be water (steam), or possibly unburnt fuel which causes white smoke sometimes.

Does the car show any signs of overheating? Headgasket(s) possibly.

As mentioned a fuel system air leak would cause these symptoms, but maybe yours is a very slight leak and needs all night to make starting difficult.

Just some thoughts!
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Sat 25 Dec 2004 22:01
Starting problem on Audi A6 2.5 TDI - DL
Correct - tight valve clearances do indeed cause poor cold starting but the Audi motor uses hydraulic tappets.
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