M30 intake vacuum and removing the oil cap - more

[Jeff N.]

OK - did the idle test and paper test.

Idle test - rolled the #1 pot way down. Pulled oil filler cap. No change in idle.

Paper test - placed some paper over the oil filler cap. Basically zero vacuum. Not positive or negative in any noticable fashion.

Hmmmm...mystery huh?

[genphreak]

A blockage in the rocker cover pipes leading to the intake vacuum?
A big leak elsewhere in the rocker chamber?
Broken pipes?

As many successive presidents have said a few times... 'The leak is in there, somewhere'

[Martin in Bellevue]

Well, could be that breather tube to the valve cover is effectively venting to the open atmosphere. Try plugging both ends of that little hose & check for vacuum change.
I did this for a while with the map setup, searching for more stability in manifold vacuum. It resulted in 20+ inches Hg, read from the map sensor taking vacuum off the test port to the brake booster.

[Jeff N.]

I think some old wine bottle corks will do the trick!

Well, could be that breather tube to the valve cover is effectively venting to the open atmosphere. Try plugging both ends of that little hose & check for vacuum change.
I did this for a while with the map setup, searching for more stability in manifold vacuum. It resulted in 20+ inches Hg, read from the map sensor taking vacuum off the test port to the brake booster.

[Jeff N.]

Two corks. One in the elbow end of the valve cover breather and one into the bellows boot. Essentially removed the plastic elbow.

With the corks in, I get slight vacuum at the oil filler as measured by Jeff's paper test. This must be the transfer of the manifold vacuum via the 3mm line to the valve cover now that vent to the intake is plugged.

Manifold vacuum sitting at 18 inches corked or connected as typical.

At idle, with the bellows uncorked (big hole in intake track post MAF) the car idles fine. No change from connected.

[Bill R.]

rpm it should be fine.. just out of curiosity did you remove that smaller vacum line and check it for obstruction all the way up to the manifold.. I'm just wondering if its restricted and not sucking as much as it should.

Two corks. One in the elbow end of the valve cover breather and one into the bellows boot. Essentially removed the plastic elbow.

With the corks in, I get slight vacuum at the oil filler as measured by Jeff's paper test. This must be the transfer of the manifold vacuum via the 3mm line to the valve cover now that vent to the intake is plugged.

Manifold vacuum sitting at 18 inches corked or connected as typical.

At idle, with the bellows uncorked (big hole in intake track post MAF) the car idles fine. No change from connected.

[Martin in Bellevue]

Maybe I wasn't clear. I was suggesting to block the small vacuum line to the breather hose, not the breather hose.