Mysterious smoking 930

[halfbad]

I am stumped here guys. Recently replaced the turbo on my '87 930 because I was sure that the seals were gone. The dead giveaway was the massive amounts of smoke being emitted from the exhaust pipe upon starting and running. Unbelievable amounts of smoke. After having the turbo rebuilt and reinstalling it I seem to have the same problem. Yes I cranked the engine over without starting to pump oil into the turbo and checked the accumulator to be sure that oil was passing through it before starting the car. When it did start there were once again the big clouds of oil vapor in the exhaust. The reason I say vapor is that it does not appear that the oil is actually burning in the combustion chambers. I could be wrong but the smell and color of the clouds is not right. I checked the oil level and it is not overfilled and I went so far as to drain the crankcase and then dumped this oil into the oil tank. Then I restarted the car and it ran perfectly and no smoke-for about three or four minutes. Then gradually the smoke returned as before. I can repeat the oil drain/restart routine and clear the smoke for about the first three or four minutes of running time and then we are back to the big cloud. I have disassembled the induction system/intercooler and checked various tubes and hoses and am not finding any oil residue of any consequence anywhere. The car has about 56,000 miles on it and ran perfectly before I took the turbo out and it still sounds fine and starts and idles fine. No big drips anywhere either. Could oil be getting into the hot exhaust system through the waste gate or other device and vaporizing in the exhaust components? Or is it possible that the turbo is passing oil into the exhaust system and is actually still at fault? I am at a loss as to what is going on and have searched other sources to no avail.

[Gumba11]

Are you just getting a puff on start up and then it clears and runs fine, or does it smoke under boost all the time?

A puff and sometimes a large one is perfectly normal for our turbo cars. N/A cars can do it too although I seem to see it most frequently with turbos.

You can talk to Stephen Kaspar at Imagine Auto and he can expand on the exact cause but if your problem is as I explained above, you have nothing to worry about.

Hope this puts you at ease, I wondered the same thing when I first bought my 930 now 6 + years ago.

.................................................. ...C

[halfbad]

Hey thanks for the response. Once this thing starts smoking, it is continuous. I don't even get to the point of any boost and it will smoke. It smokes when it is idling once it starts. As I have stated the only time I have been able to get it to stop is when I drained the crankcase and put this oil into the oil tank. I am wondering if it has anything to do with the scavenge pump. I have noticed having been through this routine a couple of times that on sitting after I have drained the crankcase, the oil seems to drain from the oil tank into the crankcase over night to the tune of about a quart and a half to two quarts or so. I don't know if this is normal-does the oil drain from the oil tank through the scavenge pump into the crankcase, or is there a valve that is supposed to prevent this? Somehow the oil in the crankcase seems to be related to the smoke problem but I am not sure. I may still have a faulty turbo.

[TurboBert]

It could be a couple of things but it sounds like the drip tank is overfilling and backing up into your exhaust. This can be caused by a bad scavenge pump or too much oil flow to the turbo.

After market headers tend to have smaller drip tanks and are not vented - this can cause problems. If your exhaust is stock, then the second thing is to check to ensure the flow-limiting ball bearing is still in position. This is located under the pressure switch which is located in the back of the engine bay behind the air cleaner.

I did flow checks to verify flow rate and scavenge pump operation when I had similar problems. For more information you might want to refer to this thread:

930 Oil Drip Tank Fills When Engine Is Off -->Causes smoking

[halfbad]

Thanks TB, I will check the oil feed line and the ball bearing routine as well as the drip tank tonight and report back.

[Gumba11]

Thanks for the link also TB, I learned something new today!!!

YAY.....................................C