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Hi everyone-
I had convinced myself that I had a vacuum leak, because my car stumbles a bit during idle and hard acceleration (new DI cassette, BTW, gap 1.0 mm, but no dielectric grease yet), and during "compression braking" the turbo boost gauge doesn't go very far into the white. I hooked up my vacuum gauge today to the line to the boost gauge and did some calibrating. The line to the boost gauge attaches to a Y connector below the throttle housing. The two other lines from the Y go to the back of the intake manifold, at the cylinder #1 end, and the hooter valve. Hooking up the vacuum line to the hooter valve shows that it will only allow 12 in. Hg of vacuum (that is, 12 in. below atmospheric pressure), which is exactly where my turbo boost gauge needle stays during compression braking. It will hold this vacuum OK, but no more. So it's the hooter valve that's doing this. Is this normal? I know that intake manifold pressure with throttle closed at high rpm should be lower than this, or more vacuum. Piston engine planes will hang out at about 10 to 12 in. Hg (which would show as about 20 in. vacuum on my vacuum gauge) in this situation.
My other question concerns the charcoal canister. The two lines to the charcoal canister hold vacuum well, but the canister itself does not at all. However, it has holes in the bottom, so I would expect it wouldn't hold vacuum. But, then, why do vacuum lines go to it? What does it do, anyway?
thanks in advance.
Erik A
'91 9kt 119k miles
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