Flatspot / Wavering Power Delivery

[chopper602]

New to this list, so I hope this post is in the right area ...

I have a 2003 Audi A6 TDi about 50,000 miles on the clock and serviced less then 1000 miles ago (at dealers). When the throttle is constant (or with cruise on) the power delivery is not very constant, revs don't change but you can feel the car wavering in delivering the power. It's also giving quite a bit of black smoke too, not ALL the time, but I never really get any on my Passat (with a similar engine). Acceleration is great and smooth, it's just when on constant throttle.
Any ideas what the problem could be??

 

[Broken Byzan]

I would assume the MAF is playing up, remove the wiring from it and blast up the raod to see if its any better, if it is, then you lnow what you need to buy.

HTH

 

[fjtwelve]

sounds like the N75 to me,i had very similar symptoms

 

[chopper602]

sounds like the N75 to me,i had very similar symptoms

Sorry - I have no idea what an N75 is :thumbsup: ?
A friend did suggest it could be the exhaust recirculation valve, but couldn't say without seeing it.

(Edit : The N75 is the VW/Audi part identification number for the wastegate by-pass regulator valve.) Google is my friend .....

Is this something that can be tested or changed by someone more used to working on a 602cc 2CV engine?
<grin>

 

[Broken Byzan]

You don't have an N75 as you have a diesel, it could be the EGR valve, i believe there is lots of info available on how to remove and clean it

 

[fjtwelve]

There's an N75 on mine , also known as boost control valve, sits next to turbo. I had almost identical symptoms to this, increasingly intermittent loss of power, black smoke, and it was cured by replacing the unit. Take your choice.

 

[chopper602]

It's been to the dealers and hooked up to the 'puter, no faults found. They checked all the vacuum hoses and applied a vacuum to the EGR unit (which the tech reckoned could have moved the valve past it normal range), which seemed to fix the problem initially, but after a run to North Wales and back it's back to what it was doing - so do I spend £210 and get a new EGR fitted?

 

[fjtwelve]

Try tdiclub.com, there's shedloads of info on what to do with the EGR, you should be able to confirm its the problem or eliminate it.

 

[chopper602]

£216 later and one new EGR valve later the problem seems cured. Thanks for the help in pointing me in the right direction.

On a totally unrelated point has anyone used 'Millers Diesel Power Plus' fuel additive - comments??

 

[chopper602]

Wavering and flatspot was cured with the EGR valve replacement, but the car was still making a LOT of black smoke. Been back to the dealers today and the bottom turbo hose was split causing the car to overfuel, hence the black smoke. Car is cured now after that has been replaced, lovely smooth power delivery and a LOT quicker than before.
For good measure I've just put a healthy dollop of Millers Power Sport 4 fuel additive in too
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