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      07-11-2012, 04:19 AM   #45
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doughboy's Avatar
United Kingdom

Drives: 2016 M6 Gran Coupe LCI
Join Date: Jan 2009
Location: UK - Midlands

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H, missed this thread!

Compression test will prove rings, valve seats and head gasket. It would be a good start and is easy to do for a garage.

Leaks leading to unburned oil or fuel in the exhaust will destroy your CATs and your O2 sensors if not sorted.

Any startup problems with the HPFP will just lead to excess cranking as the ECU won't open any injectors or fire any ignition until fuel is up to pressure and ready to go. So it may give more cold 'cranks' for oil to be drawn in from any leak before firing thus giving a larger 'puff', if that makes sense?

I agree, when cold, oil in the turbos would't 'puff' blue smoke on start up. It needs to be oil in the combustion chamber for that to happen.

When not running, so you get a start up 'puff', excess oil can only get in the combustion chamber in 3 'gravity assisted' ways:

a) leaking head gasket between oilway and combustion chamber
b) leaking valve stem seal allowing oil to run down a stem from the cam chamber above (past open valve, or pooling on a shut one)
c) oil in inlet manifold running in past open inlet valves, or pooling behind shut valves and being drawn in on start up.

If its a) then this works both ways and will pressurise the oilways/crankcase with combustion gases when running, exacerbating any problems with the PCV, or it will suck oil in to the chamber when on overrun (throttle closed). Has anyone followed you to see if it smokes constantly on overrun, or gives a big puff when you get back on the throttle after overrun?, I suspect it will, as to lose as much oil as you are it can't just be start ups. I also think it will not smoke under acceleration.

If its b) then again it will also smoke on overrun or when re-applying throttle.

If its c) unlikely as you've change the cam cover and integrated PCV cyclonic filters.

BTW mine never uses any oil ever. It's never gone down from 'full' between any oil change (6-8K changes, so i've never put any top-up in it in 40K.
E90 330i 6MT gone. E91 335i 6MT gone. AMG E63 Estate gone. M6GC current...

Last edited by doughboy; 07-11-2012 at 04:38 AM.