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Smoke On Overrun

waxer52

By waxer52,
in Engines & Forced Induction

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waxer52 Enthusiast

waxer52

Posted
Posted

Smokey, Misfire (valve stem seals maybe)

I have a rebuilt rb30 bottom end with new rings and bearings. New standard head gasket and an rb25det head.

I have got a misfire from idle and it struggles as you accelerate gently (wideband reads lean as expected due to misfire).

My crankcase breather is just venting to air at the moment with very little smoke at idle, but if I kink this pipe I get excessive smoke from the exhaust on deceleration. It still smokes a bit a idle from the exhaust.

The smoke is more white than anything, but has a slight smell of oil.

I have done the usual search and come to the conclusion its the valve stem seals.

Am I right?

Can bad valve stem seals cause a misfire?

P.s. I have wasted spark running perfectly, fuel pressure and injectors are ok, afm is ok.

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https://www.sau.com.au/forums/topic/299729-smoke-on-overrun/
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SECURITY Grand Master

SECURITY

Posted
Posted (edited)

connect your crankcase breather asap to see if it stops it THEN see if you still have a problem THEN we can start ruling things out. common sense would tell you to connect anything thats supposed to be connected to see if its causing the problem, and i dont mean blocking it off... connect it as standard.

its happened before - dysfunctional PCV has caused an oil problem on other cars including my own. start from there.

Edited by SECURITY
gotRICE? Veteran

gotRICE?

Posted
Posted

SECURITY saved my life with the same situation!

Stock RB25, catch can setup with blocked PCV, would smoke just after start up when i took off from lights, and came to a stop.

Reconnected PCV, never seen another whiff :D

Defiantly never blocking the PCV again.

waxer52 Enthusiast

waxer52

Posted
  • Author
Posted

Im running msd coils in wasted spark mode. Cas has been replaced. Plugs at 0.8.

Misfire happens from startup most of the way up the rev range have not taken the revs over 4000rpm as mototr has only been built and not mapped yet.

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