grandfunk

Just got done installing a mechanical vacuum/boost and electric fuel pressure set in my car. Took it out for a spin and the boost gauge is reading way off. At closed throttle its reading a perfect vacuum and at wide open it approaches 0 maybe gets to 1 pound.
Correct me if I'm wrong but if it were leaking wouldn't it be reading around 0 and not be moving off that point very far in either direction? I walked the line down for kinks and all the connections are nice and tight. Car is running nice and smooth so really no indication of a vacuum leak as far as that goes. Anyone seen this before?

157dB

You tapped in where for this boost guage?

hammeron

idling with stock cams and your idle set around
750, you should see roughly -20 to -23 of
vacuum. if your not seeing anything close to this,
then either there is an issue with the gauge
itself, or maybe there is a vacuum leak.

based on the details you have provided, that's all
i can say at this point.

grandfunk

I tee'd it off of the fuel pressure sensor vacuum line. The tee for the boost gauge is behind the tee that runs over to the bypass valve. The problem isn't that I'm not seeing enough vacuum, its pegged at 30 inches and won't go above ten unless I have the gas to the floor in which case it still won't read a positive pressure.
Maybe I'm not understanding the style of gauge autometer uses but with the gauge disconnected it should read 0 right? I'm thinking this gauge is just way out of cal due to some sort of physical shock it received on its way to me. With the engine not running the needle rests on 30" which just doesn't seem right for a mechanical pressure gauge.

157dB

iNSTALL IT after THE SUPERCHARGER.
Fricken caps lock.
The fuel pressure bypass is the wrong spot.

Yes, at rest, it should be 'zero' pressure and vacuum.
A reading of 30"s of vacuum is wrong unless you
and downshifting really hard.
Its almost impossable to pull a perfect 30"s of vacuum
without the use of special diffuser vacuum pumps...

Diabolical!

I have my boost gauge tapped in the same spot he tapped his and it works fine. It sounds to me like he crimped the tubing when going through the firewall.

BruceH

......

Simon1

Why dont you try blowing through the tube and see if you can hear a leak or feel ressitance? Remove it from the FPS line and just blow into it. That's the same line I use.

grandfunk

Thanks for all the suggestions.
I'm pretty sure the gauge is just broken. I took it out and noticed I can move the needle to wherever I want by just tapping the face, it will come to rest pointing downward at any degree around the face. It just moves to the lowest point when you agitate it so its just spinning freely. It just happens to start at 30" vacuum because it is coming to rest on the stop peg. The reading also changes at steady throttle when I tap it as the needle slips around the drive, always in the direction of gravity whether its on the left hand or right hand side of the gauge to begin with.
I can make it read 20 pounds of boost if I want to at steady throttle by just moving it around. Its obviously not an accurate reading and not due to any sort of problem with the line. Feel pretty dumb I didn't realize this before the install.

Vapour Trails

Yes your gauge is broken.

I dropped my first boost gauge and the needle stuck at 20 psi boost, but it would still respond to changes in pressure.