Vaccum @ Idle On Stock Cams

[bry2gdsm]

Noob Question... I've Searched But I Didn't Found Much

So i hooked my autometer boost gauge with a hose (not the tubing) to my car & it reads 15 in/hg of vac @ 800.00 rpm on idle.. (this was with the car fully warmed)

Do You guys think i have a leak? What Should be the normal reading?

Thanks & Sorry For The Noobness..

 

[JayJones]

mine reads 19 to 21

 

[bry2gdsm]

Does Having A Low Vac On The Gauge Mean You Have Leaks On The Intake Manifold Only Or On The Whole System?
I'll Have To Do A Boost Leak Test Then..

 

[1996dsm]

Mine reads 15 in vac. also, never thought of it being a prob. If it is i would like to know also.

 

[jrohner]

My 1G with stock cams reads around 19 at idle. For a leak to make you read low on vacuum, it would have to be after the throttle, meaning in the intake, throttle body, vacuum hoses, etc.

 

[rich3389]

Should be around 20 inhg.

 

[2qik4u]

16 to 20 if fine for most any EFI system. mine reads 16 at idle of 860rpms and i just did a vac leak test and found no leaks at all.

 

[ThomasG-1b]

Should be around 18-21. Turbo cars are a little lower and built NA cars running alot of timing is higher. My tb shaft seals are leaking and I can hear it just at idle. I read about 15 hg.

 

[bry2gdsm]

I've just checked all the manifold lines (the one in the middle of the intake manifold,the little one on the right manifold & the one that has a "p" on the throttle body) and those have no leaks.. Those are the only ones that are hooked since i've removed everything else... & including egr valve lines... What could it be? i've recently installed a vrsf fmic recently so that could it be leaking on the throttle body gaskets or something? or having big injectors & bad plugs could leak? i have 880cc & the plugs are a little bad... so i need to change them..
Any Suggestions?

 

[And_44]

I have an almost stock 1g. I did the vacuum line delete to eliminate a large amount of vacuum leak locations my vacuum at idle is 18-19 and never changes, my idle runs between 750-850.

 

[knochgoon24]

Replacing the throttle body shaft seals bumped my idle vacuum from -17inHg to -19inHg on stock 2g cams.

The switch to Comp101200's (272's) decreased my vacuum to -15inHg.

 

[bry2gdsm]

What Do you guys think it is? the seals? Need Opinions Please..

 

[knochgoon24]

Do a boost leak test. Listen for leaks around the throttle body, intake manifold, and fuel injector seals. Use a little soapy water and look for bubbles. Move the throttle while the system is pressurized. Sometimes the seals won't leak with the throttle closed, but will leak when the throttle is cracked open.

That will help you narrow it down.

 

[bry2gdsm]

Okay.. I Will Try That & let you guys know..

Thanks knochgoon24

 

[Strm Trpr]

I've replaced every single part that could leak air except my brake booster hose.
I can put in 30psi but it leaks out in about a minute.
My vac at idle with 2g cams is 15ish always has been.
I suspect the PO hurt the motor some time ago.

I do not burn any oil, and I do not smoke.

Dry Compression numbers are as follows:
#1 - 170
#2 - 175
#3 - 150
#4 - 175
Added a cap full of oil, and no change.

I did Sea Foam twice.
Both times half a can thru the BOV hose, and the other thru the AFPR hose.

Not sure what's wrong, but cylinder #3 is not right.

When it's hot out and the A/C is on, it dips down to 13in/Hg...

 

[EclipticalGS]

I pulled -21 stock cams, -17 272's

 

[1995gsx20g]

load directly affects vacuum so if the a/c or head lights are on it should read a little lower.

if its really bothering you i would do a leak down test even if you did a compression test and it checked out pretty good.

i had a bad coil that didn't cause a missfire but caused a weak spark and affect the vacuum by a few inches of hg

another instance was when i had a 255 high pressure pump in without it being rewired and if i turned the blinker on the idle would drop with the blicker along with the voltage. i also didn't have a afpr either.

 

[Locke]

My stock 1g reads 20-21"Hg at idle.

Should be around 18-21. Turbo cars are a little lower and built NA cars running alot of timing is higher. My tb shaft seals are leaking and I can hear it just at idle. I read about 15 hg.

The opposite is true. Turbo cars tend to have more vacuum at idle than NA cars, due to the added valve overlap in NA cars. (even stock)

I've replaced every single part that could leak air except my brake booster hose.
I can put in 30psi but it leaks out in about a minute.
My vac at idle with 2g cams is 15ish always has been.
I suspect the PO hurt the motor some time ago.

I do not burn any oil, and I do not smoke.

Dry Compression numbers are as follows:
#1 - 170
#2 - 175
#3 - 150
#4 - 175
Added a cap full of oil, and no change.

I did Sea Foam twice.
Both times half a can thru the BOV hose, and the other thru the AFPR hose.

Not sure what's wrong, but cylinder #3 is not right.

When it's hot out and the A/C is on, it dips down to 13in/Hg...

This is at the turbo, or at the LICP? 30psi lost in a minute during a BLT on the LICP is not very bad. Did you check your compressor cover for a leak? This is a common place to leak.

load directly affects vacuum so if the a/c or head lights are on it should read a little lower.

if its really bothering you i would do a leak down test even if you did a compression test and it checked out pretty good.

i had a bad coil that didn't cause a missfire but caused a weak spark and affect the vacuum by a few inches of hg

another instance was when i had a 255 high pressure pump in without it being rewired and if i turned the blinker on the idle would drop with the blicker along with the voltage. i also didn't have a afpr either.