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300 Tdi smoke on overrun


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Clouds of bluey smoke pour out the exhaust on low throttle overrun. None with no throttle, and none with enough. I assume stem seals, but would I not get smoke with no throttle as well like my my 19j did?

The exhaust manifold gasket has gone a bit and is leaking in case that would have any effect and she smokes the same colour a bit idling when cold.

I get black smoke as well, but i imagine this will be due to standard fueling with no intercooler fitted.

Is my assumption of valve stem seals likely or does anyone have any other suggestions?

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No harm in checking the stem seals, as they're certainly cheaper than the turbo.

You can (carefully) lift the collets off if you have the appropriate tool to lever the washer+spring down (I made one up following a guide that I found somewhere on the net - can't remember where), and then lift the seals off to check their condition. But youi'll need to rotate the engine to ensure that the relevant piston is at the top of its travel so that the valves don't disappear down the cyllinder!

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Are there any other symptoms for timing being out, besides the smoke I mention and noise? Noise is hard to guess, the rest of the vehicle rattles too much to tell.

I think I'll be popping the head off just to have a look at bits and pieces anyway, so will do the stem seals when I have things apart. I'll check the timing if the smoke persists afterwards.

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I've not had anything apart yet, but I have noticed that the engine seems to miss when it smokes so it could point to a fuel issue such as timing? Obviously, I need to actually do something to narrow it down, but any speculation is welcome...

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I had a similar issue with mine where it would push out loads of white smoke at overrun and would splutter a bit if you revved it hard after starting it when cold. I checked the timing and it was more or less OK but was slightly retarded. I advanced it a little and it's been OK ever since.

Put the engine in TDC using the mark in the flywheel, remove the inspection plate over the front of the injection pump pulley and get a 9mm drill bit and push it in the hole. If it goes in then the timing is (more or less) OK. You might still be able to advance it too which will make it a little more clattery but it will hopefully cure your issue and could potentially give it a little more pep.

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  • 4 months later...

Taken me this long to get time off work to take the front cover off and lo and behold: the crank sprocket is loose on the crank, so presumably a new woodruff key should sort this. (Along with a timing belt, tensioners and new sprocket)

Will be nice for her to not choke everyone around her anymore...

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