Vacuum on boost gauge.

[my98GST]

What should the perfect vacuum be? Mines reading 10 vac on my boost gauge. Is that normal or is something wrong?

 

[mpb87]

10 seems low, mine sits between 15 and 20 at idle (i'm assuming thats where you mean it sits at 10)

 

[kenamond]

Mine's at around 15 at idle and 20 when motoring the engine (clutch out, off the gas, decelerating above 3k rpm).

 

[andymoraitis]

Unless you live in a high altitude location, typical vacuum (without aftermarket cams) is around 18-20 in./hg. If your gauge is stitting on "O" with the motor off, you can rule that out. Your best bet is to perform a vacuum leak check by spraying carb and choke cleaner on your vacuum lines with the motor at idle. If your idle changes, you have a leak and need to repair/replace the line.

For comparsion, I live 800' above sea level and I see 15 at idle and 25 at deceleration on a stroker with Comp 200's.

Good luck and let us know what you find,

Andy

 

[kenamond]

I'm at about 7500 feet.

 

[2DaTrakNow]

You could always double check to see where you hacked in for your gauge line. I wasnt thinking the first time i hooked mine up, and i put it in a spot with a few restrictions. My vaccum was only at about 10-12, and my boost only read about 4-6 psi. I then relocated my boost/vaccum gauge line, and now i am back to normal with about 18 in/hg vaccum, and about 10-11 psi. So you could always double check that if you wanted to.

 

[dnhieu]

i have been having this very same problem since i have had this new talon of mine. i have ABSOUTLY no boost leaks and my vacumme is at 9 untill the car warms up and it sits between 10-11hg. my boost guage sits near 1psi when the car isnt on does that mean its diffective? if i let my external wastegate control boost it sits perfect at 1bar/14 psi so im thinking the guage is still good. am i wrong?

thanks in advance
david

 

[my98GST]

When the car is off, the needle sits on 0. When at idle, (first start up's after has set for a bit) it will read 20ish. Then it will suddenly jump up to 10. Where are all the vacuum lines that I need to check? I'm unfamaliar with vacuum lines. It didn't start doing this until I did my turbo swap..

 

[GSntncT]

When the car is off, the needle sits on 0. When at idle, (first start up's after has set for a bit) it will read 20ish. Then it will suddenly jump up to 10. Where are all the vacuum lines that I need to check? I'm unfamaliar with vacuum lines. It didn't start doing this until I did my turbo swap..

Well, if you are venting, and/or have anything to the equivalent to 264/272 cams, that will affect your vac readings. From there, I personally would take a look at your intercooler piping, ensure the bov has no kind of leak, the vacuum line coming off the bov, and the vacuum line where your boost gauge should be t'd into, which is the vacuum line that runs from the intake mani, to the fpr.

 

[my98GST]

..............I uh..... guess.... It helps if the vac. line is pluged up to your fpr huh?

Now its sitting at 20.

 

[oldman]

which is the vacuum line that runs from the intake mani, to the fpr.

Be careful when giving newbies this suggestion as most still has the Fuel Pressure Solenoid hooked up. The boost gauge should be tapped in between the intake manifold and the FPS, not in between the FPS and FPR. Tapping the FPS/FPR line will result in incinsistant reading similiar to what my98gst is reporting.

 

[GSntncT]

..............I uh..... guess.... It helps if the vac. line is pluged up to your fpr huh?

Now its sitting at 20.

Well, good. At least it was something simple.

Oldman: Thanks for pointing out something that I didn't even think about. Correct as usual bro.