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ricksgem 10-04-2007 07:48 AM

1994 911 Turbo Smoking, Can't Figure This out!

I'm at wits end.

I'm billowing blue smoke. Then engine was rebuilt 5000 miles ago and runs great, but when the car gets warmed up, MASSIVE amounts of blue smoke come out of the exhaust!

I realized I hadn't rebuilt the turbo when I had the engine rebuilt, so I pulled it and sent it off to I thought perhaps the seals were leaking that that was where the oil was coming from.

I put the rebuilt turbo on the car and the problem persists. After I drove the car oil was DRIPPING out of each tailpipe.

The engine oil is at the right level, and the engine pressure reads normal on the gauge. I replaced the air filter in case that was part of the problem.

So ASSUMING the rebuild on the turbo was done properly, and assuming the same for the engine 5000 miles ago, what can the problem be? Can blowby account for this much oil, and if so how do I determine that?

I'm reading about the possibility of a "plugged engine crankcase breather" but I can't seem to find it, does my car have one? (my repair manual has been on backorder FOREVER!)

How could I test for a restriction in the turbo oil drain line?

I'm truly stumped, ANY help would be GREATLY appreciated. There's not a good mechanic nearby.

h20cooled7 10-04-2007 08:09 AM

im gonna take a stab, possible cracked rings while assembling the cyls and pistons? try a leak down test on all cyls and see what you come up with . its probably something that was done when the motor was rebuilt.

AFM744 10-04-2007 09:57 AM

Haven't posted on PP for a while, but I'm back with a '92 C2 turbo after years of Audi bi-turbo tuning experience.
My bet: oil return obstruction. Whether your return line is not draining into the engine or you did like I did once and left the shipping plug in the turbo oil return flange. I did this once on an S4 and literally had to hang the exhaust for a week to drain quarts of oil out. Especially on KKKs, if the oil cannot easily drain out the drain line it will happily make its way into the impeller housing and smoke like a forest fire.

ricksgem 10-04-2007 10:52 AM

An obstructed return makes perfect sense, but what I don't quite get is WHERE IS THE "RETURN TUBE"? There is one oil connection to the turbo, is there a "tube-in-a-tube" there or something? Is there an easy way to test it?

I am strongly suspicious that my problems lie on the turbo end rather than the engine, because the engine purrs so beautifully and there is no smoke AT ALL until the turbo kicks in.

AFM744 10-04-2007 11:40 AM


no smoke at all until boost? When I left in a shipping plug on one of the K04s on my Audi there was smoke almost the instant I first started it.
Pull the sparkplugs and see if they're oily. If they're clean then you know the leak is downstream of the engine. It's possible to have oil dump into the compressor (cold) housing too, which would blow oil up through the intercooler and make a mess of the whole intake tract, and give you oily plugs. But the smoke only on-boost has me scratching my head. Rev the engine in neutral (and get the oil pressure up) without making boost, this may diagnose whether it's actually boost or oil pressure causing this.
I made plenty of mistakes on the Audi, and got to help others sort out their's, but I haven't torn apart my C2 yet so I'm going on general logic. If it's only smoking ON-boost then I'd start looking real hard at the case breather plumbing. This was actually a TSB turbo failure cause on my Saab; the case breather would clog causing the case pressure to build, backing up turbo oil draining.

im4duke 10-04-2007 11:53 AM


Originally Posted by ricksgem (Post 3513528)
WHERE IS THE "RETURN TUBE"? There is one oil connection to the turbo...

Does your turbo not have inlet (top) and outlet (bottom) oil lines similar to this?

ricksgem 10-04-2007 12:28 PM

I should have been more clear, I'm virtually certain the turbo is dumping oil into the intercooler, and that all the plugs are oil-soaked, since when the turbo kicks in the engine glugs and the smoke pours out. It takes a few seconds for the engine to recover if I clutch, which I imagine is the oil burning off the plugs.

As to the oil return tube, I took exactly one oil tube off and put it back on when I replaced the turbo. I will take that tube off and see if there is an obstruction, but I don't see anything else that could be for return. Unfortunately PP doesn't have a pic of the 94 turbocharger line, which is different than the 91-92.

If someone understands this better than I, please let me know, I'm feeling rather dumb today.

patkeefe 10-04-2007 12:54 PM

You may want to look through this. It only took me six months to figure this out.

964 T #304 10-04-2007 01:21 PM

The turbo has to have an oil supply & return line . Look@ pic posted by (im4duke) above.

ricksgem 10-04-2007 01:24 PM

Okay so I'll admit I was an idiot, I found the oil feed, it isn't visible from below and I somehow forgot taking it off and putting it back on (must be all the burning oil fumes I've inhaled!)

So I assume the bottom is the return, there is a new-looking metal braided line leading into a cylindrical canister, which then leads to a rigid tube and into the crankcase.

The line has oil in it that flows slowly, anyone know what the cannister is for and how to see if I have adequate flow?

I cannot find this replacement part at PP or automotion, if it was cheap enough I would just replace it. Thoughts?

You guys are the best!

ricksgem 10-04-2007 01:46 PM

I'm starting to suspect that I'm SUPPOSED TO have a pump to drive the oil return from the turbo and it was bypassed by the previous owner. There is what looks like a pump mounted on a nearby exhaust piece, and one end has a tube (not connected to anything) and the other end goes up into the engine somewhere. It is just slightly smaller than the oil tube that runs right past it. Does anyone know if the 94 911 turbo is supposed to have a pump? I will see if I can get a pic. Even so, I have owned the car for years without a problem.

ricksgem 10-04-2007 02:13 PM

Pics of parts in question
I have a pic of the mystery cannister between the turbo and crankcase (disconnected from turbo) and the pump-like thing mounted to the exhaust manifold that is not connected. Anyone know what these are???

ayglass 10-04-2007 06:37 PM

The disconnected bit is the wastegate. Mine looks exactly the same. The cylinder coming off the bottom of the turbo should connect to that braided line that runs to the front of the engine where there should be a cam-driven oil scavenge pump to take the oil back to the fender tank. I hope this helps a bit. ...

Jim2 10-04-2007 06:52 PM

Can we take a few steps back here.

First, there is nothing incorrect with the installation of your turbo, return reservoir, return line, pump etc.

In order for the community to try and diagnose the issue, please describe in detail when the smoking began. Did it start before or after your engine rebuild?

Are there any other particlars surrounding the time when the smoking started? Anything at all that comes to mind... service work, oil change etc.

ricksgem 10-04-2007 07:24 PM

Taking a few steps back...

The car was stolen and rebuilt before I bought it, and some parts were incorrect (for example, the wrong distributor was used and spun the wrong way, spitting oil into the cap.) This is likely due to how rare this car is and how hard parts are to find, but I knew this going in, buying a $100K car with 30K miles for $35K. I point this out because improper or improperly installed parts are a possibility, though I have owned and enjoyed the car for almost 10 years.

After tracking and autocrossing for years, the engine started to lose compression and I had the engine rebuilt by a local mechanic and 911 guru in Connecticut (Al Conrad).

It drove flawlessly for the first 5000 miles on the new engine, including 1000 miles down here to Georgia, but as we were building a new house it sat for over 6 months, not something I had intended or foreseen.

It was after sitting that the problem arose, maybe the 2nd or 3rd trip, when suddenly the smoke began billowing. I read that sitting for a long time will kill your turbo seals, and that was why my focus began there. It should have been rebuilt with the engine and was not. In fact, the returned parts after the rebuild looked pretty bad, the blades on the turbine were chewed up.

Now the smoking behavior is quite predictable, a little puff at startup (keep in mind the chamber is filled with oil at the end of the previous run) and then no smoke for the first 5 minutes of calm driving. As the engine warms, you start to see some blue smoke and then if I punch it the engine glugs and the smoke billows, with BOTH tailpipes dripping oil.

I have removed the turbo oil return tube and will blow it out with compressed air tomorrow, but I doubt that is the cause unless some part of the old turbo fell into it. It had oil flowing out of it, so there must at least me SOME flow. I had wondered the purpose of that cannister before I put pressure on it, but I assume it is just for crud collection.

Absent that being the problem, I'm not sure what to do next. I will buy the equipment to do a leakdown test (the nearest certified Porsche mechanic is now 60 miles away from me!) but given that the engine sounds fine I am having a hard time believing this much oil could be blowing by, and only at high RPMs.

Okay, there's my life's story with this car, thanks again for all the help, I've learned a lot and I think together we can get this thing fixed!


ayglass 10-04-2007 07:33 PM

Let me be the first to vote turbo oil seals. You might check that out first and save some effort.

ricksgem 10-04-2007 08:01 PM

Sorry if I wasn't clear, I have had the turbo rebuilt and the problem persists. Unless the new seals are faulty, it must be something else.

ayglass 10-04-2007 08:51 PM

I suspect that my scavenge pump is bad. I posted over on rennlist with the symptoms I'm seeing. We might both be in the same boat. It's my understanding that if that pump fails, you get oil even with good seals. I'm trying to figure out how to diagnose this myself. I'll be watching this thread with interest!

Tinker 10-04-2007 10:02 PM

Why not disconnect the scavenger pump's output at the oil tank (catch the output in a can or something) and run the car BRIEFLY to see if the oil is returning to the tank?

I am wondering if the check valve at the pressure switch is stuck and just dumping oil or over-pressurizing the turbo's oil supply?


Jim2 10-04-2007 10:20 PM

Not sure if I can be of any help...

The fact that the problem showed up after sitting for six months is likely a coincidence.

Turbo seals are metal and simple in design, little to go wrong with them unless the turbo bearings fail, or are very high mileage. Sitting for long periods without use will make no difference to them what so ever.

What weight oil are you running? (Is it possible that it got changed to an incorrect, very light weight? )

Oil thins when it gets well used. Has it been neglected? Roughly how many miles since last change.

Tinker makes a good suggestion. Also consider getting a better look at the metal line from your steel braided line which goes forward to the pump and ensure it is not damaged. You might take the left tire off to do this. While you are at it, have a look at (or feel) the discharge line leading from the pump, over the transaxle, then onto the tank on the right side of the car.

If you need some pictures just ask, though the 94s might be somwhat different than the old beater I have here.

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