Vac/Boost Gauge - Boost Leak Question(s)

[TheGreatGSX]

Just installed a new 30psi Autometer boost gauge which replaced a 20psi Autometer boost gauge. The vac at idle is still reading the same which is around 18-20psi but at decel it is reading 25psi. Before it read 22psi. Should I be worried, I see most peoples Vac read about 22psi at decel.

Also I noticed that the needle is very subtly vibrating at idle which I did not notice on the old gauge, which I am assuming that maybe since it reads a broader range possibly it's a tad sensitive to vibrations? Because it's vibrating with the car at idle or at least it appears that way.

Last but not least, when I shut the car off it seems like the needle is right below the 0. If you look at an Autometer boost gauge usually to the left of the "0" is like a window:

-20
-10 BOOST
[] 0
-10 VAC
-20
The needle is setting right below that [] when the old gauge it sat right in the middle of it.

Any way to calibrate these things or is this all normal or what? Thanks in advance

Edit:
Also I wanted something cleared up for me. They say a VAC gauge can let you know if you have any VAC leaks yet they also say even if your VAC gauge is reading normally to test for VAC leaks, can you have a VAC leak and your VAC reading be normal?

 

[gofer]

Just installed a new 30psi Autometer boost gauge which replaced a 20psi Autometer boost gauge. The vac at idle is still reading the same which is around 18-20psi but at decel it is reading 25psi. Before it read 22psi. Should I be worried, I see most peoples Vac read about 22psi at decel.

No you shouldn't be worried, 25in/Hg is normal if you downshift. Vacuum isn't measured in psi (pounds per square inch) its measured in in/Hg (inches of mercury).
Boost = psi
Vacuum = in/Hg.

Also I noticed that the needle is very subtly vibrating at idle which I did not notice on the old gauge, which I am assuming that maybe since it reads a broader range possibly it's a tad sensitive to vibrations? Because it's vibrating with the car at idle or at least it appears that way.

If you think about it the movement on the needle should be considerably less because it reads in a broader range. It could be shaking like that because the gauge is broke or you have a possible leak somewhere.

Last but not least, when I shut the car off it seems like the needle is right below the 0. If you look at an Autometer boost gauge usually to the left of the "0" is like a window:

It sounds like there are a few things wrong with this gauge from the get go and I would be pissed, especially if you bought it brand new. My autometer boost gauge is a little high in the "0" window like your saying but its still at "0" with the car off.

Also I wanted something cleared up for me. They say a VAC gauge can let you know if you have any VAC leaks yet they also say even if your VAC gauge is reading normally to test for VAC leaks, can you have a VAC leak and your VAC reading be normal?

If your used to seeing 18in/Hg at idle on your gauge and for no reason one morning its idling at say, 10in/Hg then yes you could assume and start checking for vacuum leaks. Your car wouldn't be idling like it should though either so that would be a dead giveaway too. Some vacuum leaks are so small your gauge won't pick them up, the gauge isn't that sensitive.

The best advice I can give to you is to toss that crappy plastic hose running to your gauge and buy some rubber vacuum line from a car parts store. That clear plastic hose loses integrity from the heat cycles and under hood conditions and starts cracking creating all sorts of vacuum/boost leaks that could have been easily prevented.

 

[TheGreatGSX]

No you shouldn't be worried, 25in/Hg is normal if you downshift. Vacuum isn't measured in psi (pounds per square inch) its measured in in/Hg (inches of mercury).
Boost = psi
Vacuum = in/Hg.

Yes, I knew this, sorry. I meant to type in/Hg. Thanks for the reply! Still confused why it would read 25in/Hg now but read 22in/Hg before with nothing done but the boost gauge replaced with another model. And yes, I am kind of pissed, which is why I've notified the seller and will be getting it replaced (Just to be safe). My biggest concern, is the needle is outside of that "0" box/window when the car is off, not much, but still outside none the less. Thanks again man, appreciate it.

 

[gofer]

You changed gauges and your 22in/Hg vacuum when you downshift on your old gauge looks like 25in/Hg of vacuum on your new one. I mean, you said it yourself...

If you look at an Autometer boost gauge usually to the left of the "0" is like a window:

 

[ramsack]

as for the shaking, did you plumb it differently this time? it is normal. the engine generates pulses of vacuum not just consistent vac.