[mwebb]

right
more information
here goes
blue trace is crankcase pressure at idle on the VW ALH TDi engine
every one of those pressure pulse s that is not captured by the
Crankcase vent valve or PCv system would be expelled to atmosphere through the catch can plumbing -
this would be the source of the HC pollution i was referring to

the pressure pulses are much stronger off idle at cruise or WOT .

there is no way around this when using the catch can , you will be venting / wasting HC emissions that could be burned and would provide some slight amount of power while reducing HC emissions

there is no benefit to using a catch can and the system pollutes more

blue trace
i hope this makes it easier to understand , with understanding comes
responsibility
- now you can not say -
" i do not see how this is bad "

you can not put the genie back into the bottle