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Smoking On Over-run


bishbosh
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Coming home today from Devon I was descending Porlock Hill in Low 2nd under engine braking (auto box :blink: ) and noticed a significant amount of smoke exiting the exhaust.

Once back on the flat the smoke disappeared.

3.9 EFI BTW.

Any clues?

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as Les says,

V8 smoking on overrun.... tends to be Valve Stem seals, easy fix, and cheap.

,.....if also on acceleration then Piston rings, not so easy ...and not so cheap :huh:

Nige

as FF says. Overrun condition would be closed throttle so big vacuum and very little fuel delivered so if vavle stems ae leaky, oil will get sucked in and it wold be that that is burnt off.

Not entirely convinced that valve stem seals are the answer. There are two schools of though, much lie fitting switvel or procomp shock gaiters; IHBS the early ones were crappy felt/rubber O-rings that disintegrate and can cause blockages; the later rubber cup type with clips are better but you need to have different valve stem.

New valve guides are the only way (from my experience - look at my old LRE sig - there valve stems themselves wear very little).

Are you using 20/50 W?

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