RE: Wierd 4kq CIS Fuel Problem

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> > > Turbo or non-turbo has nothing to do with it.
> > 
> >         THen why is it that NA Audis run fine with no Oil Cap and the
> > Turbo motors couldn't even think of it?
> >         ARe the Turbo motors and Non Turbo motors different in this
> > respect?
> 
> IMHO the turbo motors are much more "finely tuned", the n/a will run ok
> further away from it's "ideal" settings - so a vacuum leak won't shut
> them down like a turbo motor.
> 
> But I don't really know why....
> 
... it is quite simple ... on the MC engine (possibly others, but not the
WX) the valve cover area and crankcase are connected quite directly to the
metered section of air in the intake manifold.  The reason the MC engine
stalls when you pull the oil filler cap is that you are introducing a
massive source of metered air into the intake ... it is just as if you
pulled off any other hose that is attached to this part of the intake tract.
I would imagine that this was done for emissions control reasons, but I've
never understood why no valve or restrictor was placed in the connection
that goes from the back of the valve cover to the airbox.  On most normal
cars (my '78 Fox for example) this vent line is attached to a point below
the airflow sensor plate, which allows the crankcase ventilation fumes to be
metered with all of the rest of the intake.  I've had problems with that
stupid cast hose that goes from the valve cover to the crankcase vent
causing the engine to stall, so when I put the Avant's engine back together
I'm thinking about installing a valve that allows flow from the crankcase
vents into the intake only of there is sufficient pressure in the crankcase
(IOW a PCV valve ... ).  Actually that is probably why there is no valve ...
since it is so likely that the stupid hose is going to fail and if a
restriction or valve were put in place the engine would continue to run when
the hose failed ... spewing crankcase fumes into the environment (which
includes the passenger compartment of the car) so with this solution if a
leak occurs the engine will not run ... 

... there's no "more finely tuned" to it at all ... A/F ratio is A/F ratio
... and it needs to be as tightly controlled for a turbocharged engine as it
does for a high compression NA one ...

Steve Buchholz
San Jose, CA (USA)