Loss of power - Boost Problem

[JLLL]

I need some help here.

My 96 Audi A6 2.5TDI has been getting more and more sluggish. It used to accelerate well to 3000rpm and then loose power, it would get to 4000 - eventually. Of late there been no real power at any revs. When it failed the smoke test for the MOT I though its time to get a diesel specialist on the case. Their prognosis is as follows.

No fault codes
MAF tested and works ok
No leaking hoses
Air filter ok
With (the pressure side) control to the waste gate disconnect the turbo produces 0.4 bar. Low put definately spinning.
With control hooked up theres no boost.
With some pressure applied to the waste gate some boost is measurable and peformance improves (no idea how they did this).

They couldn't put their finger on the problem but suspect the wastegate is not seating properly, which is reasonable. There recommendation was to get the turbo taken off and tested by (another) speicalist, the cost makes me shudder though :mad:.

Does anybody here have any thoughts on what the problem may be, are they right to suspect the wastgate, are there any easy fixes?

How difficult is it to get in and inspect/service the wastegate?

Are there any other test I can do to narrow it down?


All help greatly apreciated.

[rob7706]

JLLL,

I had a similar problem a while ago and the turbo had to be changed - it just wasn't turning. After that, it was OK for some months but recently it started to show similar symptoms - low power, low revs and poor mpg. All the usual suspects were examined and in some cases changed. Eventually it was the catalytic converter (despite several experts telling me it wouldn't be!) Now getting performance like never before and lots more mpg! Here's the link to my post: http://www.vwaudiforum.co.uk/forum/images/misc/subscribed.gif A4 2.5tdi intermittent, then solid, power loss (http://www.vwaudiforum.co.uk/forum/showthread.php?t=2240) Hope this helps. The cat is expensive but not too difficult to examine - but make sure they examine the front end - not just the back end of the cat.

[adamss24]

Check the boost/vacuum hoses for splits from the wastegate actuator and see if the vacuum holds. If the wastegate its jammed then it will need cleaning/reconditioing. Also you should check the intercooler for leaks as will give similar simptoms. What is the mileage on the turbocharger and how its your driving style ? The old C4 a6 5 cyl were nearly bullet proof. Also how manny miles on the nozzles ? You may wanna recondition them if they have over 100k. Also, you should check/adjust the fuelling in basic setings-Dealer job i am afraid, unless you get the right engine login code and have someone handy with Vag-Com ! Also, what is the engine code AAT or AEL ?

[JLLL]

Rob - Thanks for the info it hadnt occurred that it may be the cat, I will try and investigate this, its probably the original one still

Adam - Its 5 cyl AEL engine and I've been doing lots of short journeys in traffic unfortunately, which definatley deosnt help, however I think the car has had this prblem since I bought it. 100k on the clock, I dont know much more.

My main suspect is still the wastegate being jammed open, though it could be the the actuator thats jammed. The diesel specialist said he checked the hoses so I guess I trust him. The interesting thing he said was that he could measure virtually no boost pressure and when pressure wa applied to the wastegate boost went up rather than down as he expected.....

Its probably going to mean me or someone else removing the turbo to investigate the wastgate - Getting it off doesnt look too tricky if I've got spanner that'll reach without removing the manifold. Taking the turbo to bits sounds very very very scary. I'm hoping I can get hold of some audi workshop manuals or similar, though they'll probably just say replace it as did the *******.

The intercooler is definatley worth a check, I think its just a case of getting the bumper off

Anyone taken a turbo to bits recently?

[adamss24]

Trust me, you will have a hard time taking that turbo off mate as i did it once on my old C4 A6. You will need to take the undershield off as the oil return pipe has to be undone from underneath and its not much room there . Why they did not put the turbo on the oposite side i dont know !??! Be verry carefull not to strip the torx bolts that hold the intake manifold as it will be nearly impossible to take the charger off! Feel with your fingers for the bit to seat properly onto the heads. Also check if you have the right wastegate actuator valve as some vag models have boost actuated wastegates and other have vacuum actuated wastegates ! If the vacuum holds and there are no leaks and the wastegate opens when pressure builds( put a air line to the actuator vhen you take the turbo out) then check the catalyst but at little over 100k i doubt its the cat ...Keep us informed how things go ! Also, how did they check the MAF ? Did they check for fault codes only or they took the car for a ride and loged the airflow requested against the rpm with a vag com in measuring blocks. If you unplug the Maf ,does it runs smoother/better ? While you there clean the intake of soot/gunk as it will breathe better.