So I've been researching about pcv stuff and I keep reading the term, "unmetered" air. What exactly does that mean? I googled it and couldn't find anything...

 

basically as air enters the engine it must all go through the MAF to be 'counted' so the engine then knows in a simple sense how much fuel to mix in. If air gets in by other means NOT thought the MAf then this is un-metered air, it HAS NOT been 'counted'.

This will in turn likely make a car run richer if un-metered air is leaking in, as the PCM says it has X air so puts in X fuel to make the correct mixture, but the O2 will result in a lean condition as you actually have X air PLUS un-metered air. So the PCM compensated by richening up the mixture to make to O2 read correct. The car would run 'ok' but it is not optimum, hence it is important to check for air leaks.

With regards to the PCV stuff its all a sealed unit. No un-metered air gets in. The 'circuit' is made between the pipes in the throttle body and intake manifold and air flows around this to let the rocker covers breathe and extract bad oil vapours. if you have rocker breathers and you also run a pipe to the intake manifold as un-metered are gets though. In that case of running a breather on rocker covers you'd need to block off both pipes to throttle body and manifold such the there is NO un-metered air.

See pic below of LS1 routing:
http://www.ls1howto.com/howto/geniii...kpcvsystem.jpg

where air flows up the vent tube, internally through to both rocker covers and is extracted via the crossover and (blue) PCV return tube, but it is all 'counted' before in the MAF as it is a closed system. I have same set up but with extra catch can inline with PCV to catch all the crap rather than putting it in the engine


Hope this helps

 

Yeah mang that helps a lot!

 

What he said. But on a side note, the air that comes through the PCV system is usually not metered due to the contaminates that could be contained. This small amount of non metered air will not have adverse effects on the engine. A bad PCV valve will allow more contaminates through and that can clog up the throttle body and intake passages so it is a good idea to make sure the PCV is in good condition.

Massey

 

the air is still metered as the PCV is sealed but it will contain the contaminants you mention but any effect on running (unless you are pulling oil in) will not be noticed

 

^^ thats what I said... Trust me its in there!

Massey