2.5tdi Cylinder Compression

**evolu** · 09-05-2010,08:57 AM

Hi,

I am trying to find the cause of the smoke billowing from my A6 Avant. I have checked the crankcase breather, all is clear, the inlet to the turbo is super clean and there isn't any play in the turbo.

I plan to do a compression test but cannot find any info regarding what the spec should be.

Can anybody provide me with the relevant information?
The car is a 1999 C5 Quattro Avant 2.5tdi V6

Regards,

E

**shabazmo** · 09-05-2010,12:31 PM

If black smoke from the exhaust then this can be turbo problems or leaks in the turbo pipework. If the turbo is fine and i am not sure how you check the turbo, then air leaks in the pipework or the intercoller can lead to lack of air and an over rich mixture and hence smoke.
Vagcom should be your first port of call

**evolu** · 09-05-2010,12:38 PM

Originally Posted by shabazmo

If black smoke from the exhaust then this can be turbo problems or leaks in the turbo pipework. If the turbo is fine and i am not sure how you check the turbo, then air leaks in the pipework or the intercoller can lead to lack of air and an over rich mixture and hence smoke.
Vagcom should be your first port of call

Hi,

Thanks for the response. It isn't black smoke I am getting (black would indicate a fuelling issue).
I am getting blueish / whiteish smoke that smells distinctly of oil.
There could be an issue with the turbo, just because there is no play in the shaft, it doesn't mean the seals are OK.
But, I fear that the engine is just tired, a compression test would confirm, I just don't know what the sort of pressures are normal / abnormal.

**All-rod** · 09-05-2010,01:31 PM

Can you post engine code, that way is more chance someone will post you info regarding compression...

**evolu** · 09-05-2010,03:07 PM

Originally Posted by All-rod

Can you post engine code, that way is more chance someone will post you info regarding compression...

aaahh Yes, I knew I must have missed something.
I believe the engine is an AFB variant.

E

**Crasher** · 09-05-2010,03:21 PM

Take the cam covers off and inspect the cams for wear.

**evolu** · 09-05-2010,04:01 PM

Originally Posted by Crasher

Take the cam covers off and inspect the cams for wear.

I am aware that the cams are somewhat of a weak point in these engines, material spec of cheese I understand.
I don't see how worn cams will cause smoking though, a drop in power and poor fuel consumption maybe.

E

**shabazmo** · 09-05-2010,04:22 PM

Although blueish smoke suggests burning oil, I have not come accross cases where the block has worn. They tend to be bullet proof.
White smoke tends to represent unburnt fuel, so if cams are severely worn, the valves are not lifting as much as they should, and the cylinders are not sucking in as much air as they should. This leads to poor compression. Poor cmpression leads to poor fuel burn and therfore white smoke. The smell could be unburnt diesel rather than oil. To do a compression test the injectors have to come off and to do that the cam covers have to come off. So suggest you do as Crasher suggests. Look at the cams.
Best of Luck. it could be expensive

**Peter D** · 09-05-2010,04:25 PM

19.5 to 1 but I do not think that will be the issue. I suggest you read the ID label in the spare wheel bay to ensure you have the right engine code. Disconnect the feed into the bottom of the intercooler and see if is storing excessive oil indicating a leaking turbo. How many miles has it done. Regards Peter

**evolu** · 09-05-2010,05:27 PM

Originally Posted by Peter D

19.5 to 1 but I do not think that will be the issue. I suggest you read the ID label in the spare wheel bay to ensure you have the right engine code. Disconnect the feed into the bottom of the intercooler and see if is storing excessive oil indicating a leaking turbo. How many miles has it done. Regards Peter

Hi Peter,

Thanks for the info, but it is not the engine compression I am after but the cylinder pressure.

E