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turbojunkie
28-01-2010, 10:49 AM
Hi there,

I'm having a couple of problems with my '97 A6 2.5 TDI 140bhp and would appreciate any help anyone has to offer.

Firstly, the car takes ages for the temp to reach 90 degrees (45 mins) and even then the heater will only blow luke warm air. I want to change the thermostat. Does anyone know if it is easily accessible on this car or will I have to take it to a mechanic?

My second problem is the performance and smoke. I have seen similar problems on this forum but not exactly the same. My idle is slightly rough and I am down on power. When I rev the car once I hit about 2750rpm the turbo dies off and the revs cease to increase. There is a fair amount of black smoke too. I have tried blocking off the EGR valve but that has done no good. I tried unplugging the AFM, the car runs slightly differeently but no better. Most people seem to point at the AFM but mine is an AFM without a wire. It has a flap instead which is apparently unlikely to break. My fuel economy isn't bad but I'm just way down on power. The car has been like this since I bought it apart from when I changed the air filter. Then it ran perfect for about 2 days then went back to the way it is now. I have looked for a cracked intercooler pipe but none apparent.

As I said I appreciate any help available...

hollo
29-01-2010, 04:53 PM
Hello ,

I don't know how much help I can be as I'm no expert , but I have exactly the same model car as you with the same ( ish ) problems , and have posted a few questions on the subjects you mentioned . If you also have most of the backlights on your dash not working and a dodgy fuel sender then I'd swear we have the same car.
Anyway , Since I got the thermostat changed both me and the car get warm . It is the obvious and cheepest place to start . I do not know how easy it is to change yourself , as I got it changed as a favour by my mechanic friend , but it is not a big job.( unlike the V6 engines)
With regard to the excess smoke , my car was not down on power but would belch out black smoke . I also changed the air filter which did make a small difference , but not much . My main concern was the car failing the MOT , but it pass the emmision test OK . I put some 'stop smoke' product in the sump and try to use the premium diesel and this seems to have made a big improvment . It's not perfect , but it's an older diesel and ' they all do that sir '.
Mike .

Duffelcoat
03-06-2010, 02:31 PM
With regard smoke, it does seem to be common with these cars, however I recently did an oil change on my car myself and ran through some engine flush and changed the oil to GTX Magnetec.

I drove the car for a few days with the engine flush in it before changing the oil and now there seems to be a lot less smoke than before.

I have probably wasted a lot of time looking for things that aren't wrong with the car and it does seem as they get older they get more smokey and cleaning it out seems to help, well it did me anyway.

The car seems more responsive now as well, and there is a big improvement over when I bought the car which seems to have happened little by little by using millers fuel treatment and changing the oil and flushing regularly.

When I got the car a year ago, at 90mph on my private test track in 6th gear it would not really pick up, but now it does quite well and have had it up to 120mph on the test track.

If I find anything else that drastically makes a difference I will post, but the biggest difference to date seems to be a good old fashioned engine flush and nice clean oil!

rustybodie
16-01-2011, 07:04 PM
this is hilarious!! we bought a 1995 A6 TDI last year with almost 240000 miles on it. the performance is non existence once you get the car going. on the motorway we have to drop from 5th to 4th gear on the slightest incline and still the car gets slower and slower, right down to 45ish mph with the boot right down!
the belt at the back of the engine that apparently drives the fuel pump broke at christmas time when we were all on holiday in the north of scotland and the car seems to be lacking any kind of performance. our car, too belches black smoke tho' more especially so when it's cold.
i'm taking it to glasgow to replace the glow plugs tomorrow as the starting in the cold weather was almost impossible unless you tried susie's method of giving the glow plugs three shots at heating up and then trying to jag the engine over. works a treat but i reckon that new glow plugs won't go amiss.
interested in your engine flush and superior oil theory tho - will give it a try thanks!

rusty

VitesseEF
29-01-2011, 01:23 PM
These cars go very well indeed when in good health. They do smoke a bit under hard accleration though, especially just after a bit of low speed driving. 40mpg or better should be possible in all but continuous city driving.

Lack of power and excessive smoke both suggest lack of airflow/boost. There are a number of possible causes.

- Blocked air filter - easily sorted.
- Blocked catalytic converter. Very common now and also pretty easy to sort. The cars are not obliged to have the CAT and it can easily be replaced by a piece of straight pipe (bit harder on the Quattro as there are two CATS). You can even sell the CAT for scrap afterwards - got £ 40 for mine.
- Carbon build up in the inlet manifold. This is an effect of the EGR system which returns a proportion of exhaust gas to the inlet manifold (reduces combustion temperatures and thus NOx emissions). Unfortunately there is soot in this and it can build up in the inlet manifold passages, obstructing airflow. You can get an idea whether this might be the problem by removing the inlet pipe and inlet adaptor ring from the manifold and looking inside. It will be very black for sure, but great lumps of soot are not a good sign. Don't just chip them off in situ unless you are sure you can get them out - you don't want them being sucked in. On mine it was worst just by the inlet as this is the point where the EGR passage joins the incoming airflow. You can disable the EGR system by fitting blanking plates (I used 1.5mm copper sheet) in place of the gaskest on the EGR valve itself. This removes the big puff of smoke on initial acceleration and improves mpg a bit.
- Another easy fix is if the pipe from the rear of the inlet manifold to manifold pressure sensor (on bulkhead behind injection pump) has come off or split. This means that although the engine may be getting boost, the ECU can't see it and fuels accordingly. This makes the car very slow but shouldn't cause smoke.
- A partially blocked fuel filter can cause the car to go flat above certain rpm - again, this shouldn't cause smoke as it's an underfuelling condition.
- After this it's problems with the turbo itself (rare) or wastegate controls. Tracking these really needs the help of VAGCOM or similar software to check actual boosts against requested and watch what the various control valves are doing.
- Always worth getting the injection timing checked and reset as needed. They run alot better when it's right! Again, it needs VAGCOM or similar.

It's worth putting in a bit of effort as these cars are great when working right and the major mechanical bits are very strong and long lasting. Plenty in the 3 - 400k bracket now.

Nick