1986 305 TPI/ Just changed out my plenum and runners with a polished set. Old plenum had oil resadue in it and inside of throttle body had the same is this normal. not wet but a film of buildup. PVC is hooked to manifold, Brake booster hooked to back of plenum is this correct. On passenger side there is a hose from valve cover ot throttlebody can I disconnect and use a breather in the valve cover. Thanks

 

yes

 

Sorry - yes you can put a breather element into the valve cover. Do you have the original air breather? Does it have a manifold temperature sensor in the cover? If so, I believe you may throw a code without the correct manifold temperature reading. The varnish looking stuff may have just built up over time.

 

Not on a MAF car .
On a '86, the air to the PCV system ( from the TB port ) is metered ( measured ) by the MAF sensor.
With a open breather on the cover you have same effect as a vac leak because the computer is not measuring that air which ends ups in the intake through PCV valve.
Can do it on a '90+ engine because they are speed density and don't have a MAF sensor

 

MAT sensor is under plenum on TPI cars.
Only thing in front of TB is the MAF sensor and air cleaner

 

Just curious how the maf sensor meters anything being introduced to the intake from anywhere down the intake track.MAF can only meter what comes through the front of it.

Am i misunderstanding what youre hes asking?I run pcv on driver side and a breather on the other.The breather is just that.It lets out gasses and keeps oil residue out of your engine bay.I suppose I could be wrong or just misunderstanding his question but how can the maf meter something that doesnt flow through it?

 

That is the problem; it can't
On the stock TPI PCV system ,the air comes from the port on the TB so it has already passed through the MAF sensor and been " accounted " for. Because the ECM is aware of that air it can adjust fueling accordingly
Like the water meter at your house; the MAF measures flow. If it goes to the toilet or kitchen afterwards doesn't matter ; it has still past through the meter

Exactly.
If you allow air into engine that has not been metered ( from a open breather ) then the ECM has no way of knowing

Some have run open breathers on PCV system without problems; others have had idle problems because air is going into intake from PCV valve that is not metered

 

Opposite actually; it lets air into PCV system ( except under low vac as below )

The TPI air supply line on pass side serves two purposes
When high vac in engine ( idle / cruise ) ,it supplies metered air to crankcase to purge fumes through PCV valve
When low vac like WOT and PCV valve not operating,it allows the engine fumes to pass back from the rocker cover to the TB and into the engine to be burnt
That is why you have oil in the TB / plenum especially on older worn engines with more blowby

 

if worried about passing oil through either line into the tb or plenum, then put an inline paper filer on the lines.