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Old 09-18-2019, 07:18 AM
Xelo Xelo is offline
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Join Date: Jul 2011
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Hello again,

I am planning to do this modification also (including a catch can) but after days of studying I've stumbled upon one issue that has not been adressed (or addressed too little).

There are 2 versions for any PCV system: open and closed.
Open ones are venting the blowby gases to atmosphere, closed ones (as in this case for the M54s) are venting the "filtered" air back into the engine through the intake manifold.

Now comes problem #1: this "filtered" air is not measured .

MAF measures air coming through the intake manifold, but the one coming back from the valve cover through this modification is routed back into the IM AFTER the MAF (through distribution cover) - so there is a surplus of air going to the cylinders, although the ECU has measured less and O2 sensors will measure more.

This will cause crazy fuel trims.

Any schematic of closed PCV system on the net is described as having a venting hose coming from the air filter (so metered air) which allows the crankcase to breath.

See examples below:







Returning to the case of M54 engines: OE system does not have a supplementary/aditional valve cover breather as I remember. The only port of the VC is the one going to the CCV.

So this raises so many questions:
1) Why does the OE M54 CCV system does not have a breather allowing the crankcase to draw air from the intake
2) Would this breather be a good idea as it still allows vacuum but also protect engine seals ?
3) Where would the best connection for a breather be ? I have heard a case where the guy connected a hose from the vacuum F connector in the intake boot to the oil dipstick. If so, would this need a non-return valve (for the improbable case oil from the crankcase/oil pan would come up and flood the intake) ?




My take on this:



Last edited by Xelo; 09-18-2019 at 07:24 AM.
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