79 928 poors out blue smoke under heavy acceloration.

[72porsche914]

It doesnt smoke when its first started, only when you floor it. Am I looking at replacing the rings, or valve guide seals? The car has only 92,000 miles on it, so I wouldnt think the rings are bad. On the other hand, it doesnt smoke on startup. That leaves me to believe that the valve guide seals are keeping the oil from leaking down into the cylinder walls while the car is parked.

Is there a way to tell? Pulling the heads will be a lot easier than pulling the whole motor.

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Ed Fahrenkrug

72 914 1.7
73 914 2.0
68 912
(all under restoration)

[ckcarr]

I'm not much help but in the old days I thought that blue smoke meant rings? Perhaps (worst case scenario) a cracked ring. Maybe compression test would divulge more, but if its an oil ring maybe not.

I wish there were tons of posters over here like on my BMW1100s board. That might help.

[josh912]

Ed, try the 944 board. The 944 engine is essencially half of the 928 engine. I'm assuming that they would have the same symtoms.

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Joshua Harrison
Porsche owner at heart

[TheStig]

I'm from the 944 board and it sounds like 2 problems. Valve guides or piston rings. The only thing to make sure is a compression test. Would a compression test also reveal a worn valve guide too though???

[Roland Kunz]

Hello

Compressiontest with added oil can check the rings. A leak down can determine the exact problem.

On a testdrve you can roughly check if it is caused by the head / valve steam seals or from the piston rings.

As you descripe it i would be surprised if the rings where involved much. Yet milage doesn´t hurt a engine. Coldstart are the major wear issues on a engine especially if the driver pushes the pedal while cold and drives to short for a internal even heat up.

Grüsse

[MoonMotors]

Definentaly a leak down test is the way to go. This way you can pin point in each cylinder where or what is leaking. The leak down tool is slightly expensive so if you don't have one your best bet is to go some where. It shouldn't cost to much just to have a leak down test. We charge $ 20.00 per cylinder checked ($160 total) Good Luck

[Wayne 962]

Very good suggestions, however, I always thought that bluish smoke was from running rich? Black smoke is always oil...

-Wayne

[MoonMotors]

Smoke from the tail pipe can be a hard one to call! Smoke color can be deceptive. Normally ( this is not allways true ) Blueish smoke is oil and black smoke is too rich. But like I said this is not allways true. I allways thought thick white smoke was water in the combustion chamber but I had a 95' Ford Thunderbird spuing
thick white smoke and it was burning oil and oil deposits. Three of the fuel injectors where not working at all and those cylinders got hot and started burning everything in there. So allways double check yourself or get a second opinion. It will save you lots time and money in the end.

Brad

[Joe Ricard]

First he did not specify what color smoke. But assuming the smoke is only at full throttle. it would be black
Means to me that CIS system is whacked. Well maybe just needing a little adjustment. The fuel mixture is controlled by the warm up regulator. As air enters the engine over the sensor plate, the plate goes full open unless control pressure correctly acts against it.
What I see happening is lack of control pressure. I would change the fuel filter and eliminate all vaccuum leaks then have a knowledgeable shop adjust fuel pressure and control pressure.
Hey after you romp on it pull the car to the side of the road and see what the plugs look like. black and sooty are rich fuel. black and oily is you poor bastard.

[72porsche914]

Wow, I havn't been here in a while. The smoke is definantly blue, and has the burning oil smell. I also noticed that it only smokes at a low speed when I hit the gas. If i'm cruising at around 50mph and step on it, then it doesn't smoke. When it smokes, sometimes it will make a heavy smoke screen I'm puzzled as to why the smoke is incosistant.

I guess I will eliminate the rings only with a leakdown test. Thanks for the help guys.

[Wayne 962]

Hmmm, that doesn't sound too good. Could be rings or guides. At lower speeds (or idle), it would be easier for oil to bypass the rings and the guides. At higher speeds (where there is more vacuum pressure), you're going to get less 'seepage.'

As an alternative to rebuilding, you might want to try a bit thicker oil in your engine, as this has a tendency not to slip by the cracks and spaces in the rings and guides as much. Might buy you a few thousand miles or more...

Don't use synthetic on a car this old - it will probably be too slick, and increase your problems...

-Wayne

[jrenfrew]

I have a 78 928 and if your car is an early 79 then you might take this as your first line of trouble shooting....

In 78 and early 79 Porsch has a crank case venting pipe that is fairly short and goes from the oil fill into the air filter air box. The hose runs along the drivers side of the engine. You might try taking a look in the air box (remove the filter) and see if there is a lot of oil sitting in there. If there is you could try plugging the vent pipe and go for a test drive.

Otherwise, I'm sorry to say rings are your next most likely suspect. Plus if the car is pushing a lot of oil from the vent pipe (which was a bad design and changed in later 79) then it's going to be due to a lot of case pressure most likely caused from a ring problem. Valve guide troubles typically show up when the car is dead cold or under heavy de-accelleration it will smoke good. Under accelleration the intake vaume is at it's lowest therefore makeing it unlikely to be oil getting by the values.

Hope that helps shed some light!

[Wayne 962]

Compression and/or leakdown test will tell you for sure the condition of your valves and/or rings. It might be wise to try this now, and put all other theories to rest for the time being...

-Wayne

[Roland Kunz]

Hello

A primitive leakdown can be done with a big tire tube with a long hose and some air filled into with a electric compressor.

You are not to much interesstet into the absolute relevance from the numbers you focus more on the comparsion between the cylinders and like to hear wher the air blows out.

One over the thump:
Oil smoke while load ( overpressure ) is piston rings. oilsmoke while of throttle ( underpressure ) is valve guides.

Also check the PCV for proper function.

Grüsse

[Wayne 962]

Roland, please elaborate if you can on this tire tube idea? I can't quite grasp what the setup would be to do this?

-Wayne

[Joe Ricard]

If there is a PCV valve on my car I wouldn't know where it is hiding. which also means It hasn't been changed in the 11 years I have owned the car.
Changed darn near everything else. If you think about it my 78 should really be like a 91 thru 02 model