Audi A6 Avant 2002 - Cold Start/Turbo Cut out

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Tue 12 Jan 2021 13:20
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - The Kaiser

This is my first post so apologies if I either post it in the wrong place or inadvertently destroy any forum etiquette. My forum name is actually my car name as it is old and German (ask the kids). The main block of my car has done 240K miles, whilst other parts have done much less and my "new" cylinder head has only done 110K. I had to replace it after the original camshaft wore out at 230K, threw the valve timing out, destroyed a valve and the valve bed at the same time. In the 2 days prior to that happening I noticed a significant turbo lag had developed.

Since the "new" cylinder head was fitted the cold start is awful, sounding like it is back running on the 3 cylinders from the breakdown. After a bit it seems to clear although in idle it misses a beat from time to time.

The turbo lag remains significant but I can get used to it. Problem is that intermittently(maybe once a week) the turbo cuts out , only to restart after turning off the ignition and restarting the car.

Whilst they were working when the car came out of the garage the oil and water gauges have now signed off completely.

Any help getting the Kaiser (Trigger's Broom) to 250K gratefully received.

Edited by The Kaiser on 12/01/2021 at 13:22

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Wed 13 Jan 2021 10:34
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - galileo

Can't understand how a turbo can 'cut out'.

If the engine is running the turbo shaft will rotate unless it is seized completely. Stopping and re-starting would not cure that problem.

If you mean that the turbo does not give normal boost, but does after restart, the problem is the electronics or the linkage to the boost control system, I think VAG use variable vanes which swivel to vary boost.

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Wed 13 Jan 2021 10:46
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - RT

Can't understand how a turbo can 'cut out'.

If the engine is running the turbo shaft will rotate unless it is seized completely. Stopping and re-starting would not cure that problem.

If you mean that the turbo does not give normal boost, but does after restart, the problem is the electronics or the linkage to the boost control system, I think VAG use variable vanes which swivel to vary boost.

Any car with a variable geometry turbo needs an "Italian tune-up" from time to time to exercise the moveable vanes and linkage to prevent them seizing - this is particularly true for bigger turbo-diesels normally driven quite gently.

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Wed 13 Jan 2021 15:20
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - galileo

Can't understand how a turbo can 'cut out'.

If the engine is running the turbo shaft will rotate unless it is seized completely. Stopping and re-starting would not cure that problem.

If you mean that the turbo does not give normal boost, but does after restart, the problem is the electronics or the linkage to the boost control system, I think VAG use variable vanes which swivel to vary boost.

Any car with a variable geometry turbo needs an "Italian tune-up" from time to time to exercise the moveable vanes and linkage to prevent them seizing - this is particularly true for bigger turbo-diesels normally driven quite gently.

Exactly so, if the vanes never move their full travel, deposits of carbon build up and restrict performance.

The OP stated that stopping and restarting cured the problem, don't see how that would unstick clogged variable vanes, hence my suggestion the control system needed checking.

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Wed 13 Jan 2021 15:32
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - skidpan

We had a new 1996 Golf TDi and a few months after we bought it on the very first really hot day of summer it suddenly lost power. A few seconds later it was back. It did this on and off for the rest of the trip, bit of a nuisance since we were crossing the Peak with a 1200kg trailer on the back.

Called the dealer the next day who sent VAG Assist who since he could see nothing obvious then got the car booked in. Problem was simple, a vacuum pipe was fitted a bit tight and with underbonnet temps being hot it had become more flexible than normal. As the engine moved this tended to crimp the pipe on a tight curve which blocked the vacuum and stopped the turbo. They simply slightly re-routed the pipe to eliminate the tighter curves and during the next 6 1/2 years we never had another issue.

I guess if we had stopped and re-started the engine the turbo would have appeared fine since with a stationary car the kink would have opened up.

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Thu 14 Jan 2021 15:19
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - The Kaiser

Can't understand how a turbo can 'cut out'.

If the engine is running the turbo shaft will rotate unless it is seized completely. Stopping and re-starting would not cure that problem.

If you mean that the turbo does not give normal boost, but does after restart, the problem is the electronics or the linkage to the boost control system, I think VAG use variable vanes which swivel to vary boost.

Any car with a variable geometry turbo needs an "Italian tune-up" from time to time to exercise the moveable vanes and linkage to prevent them seizing - this is particularly true for bigger turbo-diesels normally driven quite gently.

Would you recommend any of the "engine clean up" additives that are on the market?

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Thu 14 Jan 2021 15:23
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - The Kaiser

Can't understand how a turbo can 'cut out'.

If the engine is running the turbo shaft will rotate unless it is seized completely. Stopping and re-starting would not cure that problem.

If you mean that the turbo does not give normal boost, but does after restart, the problem is the electronics or the linkage to the boost control system, I think VAG use variable vanes which swivel to vary boost.

Any car with a variable geometry turbo needs an "Italian tune-up" from time to time to exercise the moveable vanes and linkage to prevent them seizing - this is particularly true for bigger turbo-diesels normally driven quite gently.

The turbo just ceases to function, nothing at all, nada. The first time it happened was after a long run to York and back over a weekend. Car behaved OK on the way there but with noticeable turbo lag. On the way back it just ceased to have any power at all. I just about got it home and then remembered we needed milk so popped out locally again. The power was back. Since then when the power cuts back I engage neutral' coast for a bit, and then restart. Hey presto power returns. It is literally that quick.

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Thu 14 Jan 2021 15:47
Audi A6 Avant 2002 - Cold Start/Turbo Cut out - elekie&a/c doctor
You might want to check the N 75 turbo boost valve . This controls the vnt operation. The cold start issue would be a different problem . Could be valve timing ? You mention a new camshaft, is it the correct one ?

Edited by elekie&a/c doctor on 14/01/2021 at 15:49

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