For some reason, out of the blue I can't get more than 10inHg vacuum on my gauge. It's plumbed straight from the intake mani so I know the reading is accurate. However, normal driving, vacuum won't go under 10inHg.

There's no vacuum leaks (at least can't hear any) and the gauge doesn't fluctuate like it use to when there was a small leak. And I've noticed when engine braking, in any gear, the gauge hits 10 and won't go any farther. Like I said it doesn't fluctuate at all like a vacuum leak, but it just won't pull the 18inHg like they do stock.

Originally posted by eclipserstturbo
It's plumbed straight from the intake mani so I know the reading is accurate.

How do you know the gauge is accurate? Or the line or either fitting has no leaks in it?

Just because it is plumbed on a dedicated line does not mean the reading is accurate. Check everything out. At 10 in Hg your idle would be high. Is this the case?

Originally posted by CODE4

Originally posted by eclipserstturbo It's plumbed straight from the intake mani so I know the reading is accurate.

How do you know the gauge is accurate? Or the line or either fitting has no leaks in it? Just because it is plumbed on a dedicated line does not mean the reading is accurate. Check everything out. At 10 in Hg your idle would be high. Is this the case?

Have you verified the reading with a known-good gauge? I've had mechanical boost gauges fail in similar ways.

I'll try my other boost gauge when I get a chance just to verify. It's still idling fine (900-1050rpm) at 22lbs of fuel on 330cc injectors. There's no loping or unusual behavior at idle and does fine throughout the entire rpm range. Rides exactly like it has since the motor was put in, just won't go past 10inHg. But I'll try switching gauges and let you guys know what happens. Thanks for the replies.