robertbartsch

About 1.5 years ago I did a head and cam job with LT headers. The car ran rich for about two months and then I tuned it with Edit.

I blew a cam sensor recently so I took off the intake manifold. The intake ports are really caked with a thick oil-like sludge - almost tar-like.

I have a LS6 valley cover and a PVC oil catch can and flutter header tube block-off plates and it appears from the catch can that the PVC is not sucking in any crankcase oil into the intake.

Question - where is this oil sludge comming from? If the catch can and Edit tune were done a few months after the initial heads and cam could the rich condition or PVC problem from more than a year ago still result in tar-like intake ports today?


I will clean the ports out the brake cleaner and leave the intake as-is; Is this right? I suppose I could use "GM Top Cleaner" to remove any tar from the intake???

Thanks...

jimmyblue

iTrader: (11)

I have a theory about the PCV, which is that a lot
of the uptake comes "backward" through the makeup
air line fore of the TB, at WOT. Why? Because here
you have roughly zero pressure drop across the TB,
so the PCV "vacuum" side has not much vacuum and
no different than the "makeup" port. However the PCV
valve meters or checks flow while the makeup line
does not. It goes right to the valve cover. Inside
which is a nice oil fog pressurized by blowby, looking
for a way out. The light vacuum (air filter / lid / MAF
pressure drop) vs crankcase pressure is all you need
to back-flow the "makeup" line.

The TB core I ported had a big "skid mark" from this.

I think you should put a catch-can in the "makeup" line too.

robertbartsch

I'm in Japan now not near my car (NY).

Can you please describe the location of the "makeup" line? Is this the large thick line that goes around the back of the intake from the driver's side valve cover? On my car I blocked this line off...

My catch can is attached to the TB which is negative pressure vacuum when the engine sucks air into the ports.

Totally confused??? ..please helpp

Thanks...

jimmyblue

iTrader: (11)

Makeup line is the bung on top of the TB, before the
blade. Vacuum line is behind the blade, off the intake.
At closed / part throttle air is drawn through makeup,
crankcase, PCV valve, to vacuum line. At WOT, vacuum
and makeup are same pressure (=MAP, slightly below
atmospheric) so "cross flow" does not happen, flow in
both lines is (crankcase pressure-MAP) driven.