My z, for several years has had a drivers side smoky exhaust. Only when up to temp and only when the ambient temp is anywhere above 15 degrees C. I replaced the pcv valves and it made no difference, I replaced the turbo, albeit a used one and it has made no difference. The smoke is oil/blue. And is only there on tickover, as soon as the revs rise the smoke stops, I can usually control this by pressing the econ (aircon) button as this raises the revs just enough.

 

Are these symptoms turbo? Or potentially engine? What would advise my next step should be?

 

Thanks, dan

valve stem oil seals

Hot idle smoke at tick over is often a symptom of turbo seal failure, when you raise the revs the increase in back pressure created can then stop the oil passing into the exhaust. The fact you fitted a used turbo leaves a question mark there.

As I understand it, the valve stem oil seals very rarely fail on these cars and normally the smoke is more obvious at cold start up especially if the car has been standing for a few days. Then when the engine warms up the smoke clears, the opposite to yours.

For what they cost it might be worth changing the PCVs once more. Then obviously allow time for any residue oil to burn off. I heard a rumour that there are different specifications of PCV's for these cars, differences between US / JSPEC etc., don't know if its true, but l remember someone saying it could make a difference.

I'm no expert though.

Turbo seals tend to fail on the exhaust seal at which point you get grey/white smoke as it's not been combusted. If the smoke is blue, your hunting a pre combustion oil leak be it oil being sucked into the intake or into the combustion chamber.

 

Have you at any point done a compression or better still a leak down test. For the time taken this could rule out a fair few causes, esp a leak down. If the combustion is good then your sucking it in before the combustion chamber. Do you have excessive oil in the plenum? Or the intercooler pipes? I know you say you replaced a turbo but I don't know if your aware, that the opposing turbo drives the opposing bank. Ie if the passenger turbo was leaking oil into inlet it would be the drivers side that burns oil. I assume from your description your exhaust has no H or X pipe. I don't think however that's your issue. The above suggestion of valve stem seals isn't a bad shout and that may well show on a leak down test.

Which turbo did you replace? Apologies if this sounds like some egg sucking tuition, but just to be sure you're aware that the inlet plenum crosses over the intake so if the driver's side exhaust is smoking, it will be the passenger side turbo [potentially] at fault.

Well I've learned something new today, I didn't realise about the cross over situation. :)

Cheers guys, I replaced the opposite turbo last year to fix the opposite side smoking and that worked, this time I replaced the turbo on the side that is smoking and its gotten no better or worse, perhaps its pointing to engine then?? I guess I need to be looking at doing a leak down test and or compression test, most garages should be able to do these??

 

Cheers,

Yes most garages should be able to do a compression test but most will be put off once the bonnet if lifted.

Thanks, I understand about the turbo driving the opposing bank, but what about exhaust side of the turbo? If the rear turbo seal had failed on the drivers side for example then the drivers side exhaust will smoke?

 

Is there a blown up diagram somewhere that shows the route of boost?

 

Thanks

That depends solely on your exhaust. It's highly unlikely to cross over, however it is likely they are joined by a H or X section. This would mean exhaust gases are mixed before exit so both sides would smoke. Sometimes it's a simple single line from turbo to exit, only way to know is to get under there and look.

 

There is a school of thought. I've only read about this not seen it work. That the exhaust system must have an X or H, without this join the exhaust gets into a pulsing frequency that effectively sucks or pumps oil past the seals. Some have reported that restoration of this kind of join has fixed thier issue. I'm not even going to say this could be it, just you may wish to consider it as a cheap try.

 

I know you've said your compression wasn't bad, but what's not bad? Essentially those turbos are smoking because either they are being exposed to excessive crank case pressure or the real seal is so jiggered that oil is passing. Do you have cats? A lack of them is going to make the symptoms show more, due to the lack of back pressure. You say you've done done the PCV, I take it that's the valve itself that screws into the plenum? Have you investigated the front pipes? Is the brass restrictor still in place?

Thanks, I understand about the turbo driving the opposing bank, but what about exhaust side of the turbo? If the rear turbo seal had failed on the drivers side for example then the drivers side exhaust will smoke?

 

Is there a blown up diagram somewhere that shows the route of boost?

 

Thanks

 

Although these photos are for the AshSpec pipes, the inlet routes remains the same as stock. Exhaust paths from turbines and

out to the back of the car don't crossover, but may be linked (depending on manufacturer) by H or X pipes linking both banks.

 

 

^^^ That just looks sooo complicated!!