PCV valves are closed at idle (high vacuum) when the introduction of
extra air would indeed mess up the mixture. They open at low
vacuum/open throttle when the additional air intake is insignificant.
AFAIK, PCV systems work exactly the same on EFI cars but, yes, the ECU
can fine tune the mixture at all loads.
bs
Alan Bromfield wrote:
> That makes sense to me Bob. I guess with EFI systems the intoduction
> of air into the inlet manifold via the crankcase can be compensated
> for with idle speed and mixture controls. The introduction of air in
> that way probably dilutes the blowby gases too before burning them in
> the combustion chamber. It also explains what the dinky little filter
> is for that has been discussed elsewhere. Unfortunately in our simple
> carburettor engines we can't introduce air in that way without
> screwing up the mixture. The use of a PCV valve in the way Norman Nock
> advocates allows the blowby gases to be sucked out direct into the
> inlet manifold, which is a vast improvement on blowing them out of a
> tube somewhere in the region of the carb inlet.
>
> As you say it does work.
>
> On 17 March 2010 13:51, Bob Spidell <bspidell@comcast.net> wrote:
>
>> In this case, 'closed' doesn't mean 'sealed.' It means the system is
>> continuous, with an intake--the filter--and an output--the PCV valve into
>> the manifold. That's how OEM PCV systems work (see:
>> *http://tinyurl.com/yajrlzb )*. To truly breathe, you need an inlet vent
>> (the 'V' in PCV is for 'ventilation'). Ever try pouring gas from a can
>> without opening the vent hole? Pulling a significant vacuum means you're
>> not circulating the gases--the intent of a PCV system.
>> This setup does work well as is, however (I have it on my BJ8).
>>
--
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Bob Spidell San Jose, CA bspidell@comcast.net
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