Audi A6 2.5TDi Power problem

Hi, Gents, I wonder whether anyone can help me on this. I have an Audi A6 2.5TDi Avant, on a 99/T plate, and there has been this minor problem with power output for some time now, and it's
bugging the hell out of me! Imagine sitting on the motorway, doing 80, pulling up behind a truck. You see in your rear view mirror a much faster car, but you can see that you're going to overtake the lorry before he reaches you if you put your foot down to get past. So you put your foot down to get past, but nothing happens, absolutely nothing! You pump the gas pedal a bit, but still nothing. Now the faster car is upon you, and you have to slow to let him past before pulling out. When you accelerate past the truck, you pull away easily. I know the gas is applied in a "fly by wire" fashion, so I reckon there's a problem with either the send unit at the pedal, or the receiver unit next to the ECU. Can anyone enlighten me on whether this is an inherent problem, and whether there is anything I can do to stop this happening at exactly the moment when I need a bit of gas? Cheers in anticipation, Ed
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Hi Ed,
On 9 Feb 2004 05:56:32 -0800, snipped-for-privacy@totalise.co.uk (Rugbytrader) wrote:

Did you have the air mass sensor checked? It's a device sitting in the back of the engine compartment. The sucker is not wired into the onboard telemetry, so an error is not recorded.
This thingie fails quite regularly on any TDI engines and the Bosch one yours has (such as my 99 A6) does that equally often. Usually it's due to moisture or oil fumes settling on the heated wire. Then it gives a false signal (too little airmass reported) and the injection system adjusts the fuel to the airmass it sees. ==> Reduced power.
A nice indication is if top speed is not reached. Another is, that at around 2700 rpm you have a real drop in torque and you need to shift down to speed up quickly.
The workshop should be able to determine a faulty sensor by attaching the VAG computer to your car. Then they drive slow in third gear and press the pedal to the floor. When spooling up, the airmass should read something like over 800 at 3500 rpm (I posted it previously and dont have it in the top of my head anymore)
Anyway, there is a test drive cycle they should be able to run. I'm at my 4th sensor and there are Audi service bulletins on how the wiring in the car should be changed so that the post-ignition heating of the sensor wire is disabled.
The part is around 250 Euro here IIRC and is changed in less then ten minutes with a screwdriver, but if you search the web, cheaper sensors from mercedes (where only the sensor and not the complete assy is sold) can be had. Never tried one myself, but it's _supposed_ to work.
HTH
Regards
Wolfgang
--
* Audi A6 Avant TDI *
* reply to wolfgang dot pawlinetz at chello dot at *
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Probably the MAF (Mass air flow meter). Expensive to replace but a common problem.
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Check your exhaust smoke when you floor your accelerator in sixth gear. If you see a cloud of smoke in your wing mirror and the MAF is OK, it's probably a torn intake hose.
Check and see if your problem can be reproduced whenever you floor the pedal on the same slope and long gear, and if there is a difference when you apply gas gently all the way to the floor and when you floor it suddenly. If there is a consistent difference and your problem only takes place when you floor it suddenly, it could be that your hose is being strangled at maximum suction, then it would be a matter of your having your hose replaced with one that was not so flexible.
My father experienced something very similar in his '97 A6 2.5 TDI and the VAG machine showed everything to be OK, when it was obviously not.
My two cents,
JP Roberts

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Had a similar problem with a 2.5 - no power - pull onto hard shoulder, stop and switched off - tried to restart, off it went - no further probs for several weeks, then repeat, again no probs. I was told it could have been the lift (diesel) pump. As it was a company car which was being taken back I never took it any further.
Another thought?
Mike.

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