no hg or vac at idle?

[87 charger]

Ok i have a shelby charger t2 and when my car is idling my boost gauge sits on zero until i tap the gas then it goes to about ten and back to like 1 o2 psi .
Is this normal or should it vac lower at idle? Any answer will be greatly appreciated.

[Lee'sdaytona]

You should always have a vacume reading at idle. When you say tap the gas and it goes to 10---is that on the vac side? I'm gonna say your gauge is messed up
-Lee

[TopDollar69]

Idealy you want around 20 on the vac side at idle, then if you tap the gas in neutral or park, it should jump to about 10 or so on the vac side. The car really shouldnt get into boost at idle, only when there is a load on the engine.

[Lee'sdaytona]

^^20 at idle? I think not. Maybe if you have those super-sealing rings (can't remember the name now) that there was a thread about awhile ago...but stock engine should have 15 inches of vac at idle
-Lee

[87 charger]

The 10 was vaccuum i mentioned in the post . It will boost under a hard rev like maybe 2 psi tops for a split sec. I was wondering if this coud be related to the timing belt being off a tooth.

[Dave]

The 10 was vaccuum i mentioned in the post . It will boost under a hard rev like maybe 2 psi tops for a split sec. I was wondering if this coud be related to the timing belt being off a tooth.

If you rev it quickly it will build minimal boost... Wallace White does this when launching his R/T to build some boost coming off the line.

Anyways, yah your gauge is screwed up, I doubt your car would idle without vaccum.

[GLHSKEN]

Car would not idle with no vacuum... My experience.. a healthy 5-speed idles at 17-19in... A healthy automatic idles at 16-18 (drag from the tq)

[Stevien1]

Are you sure the boost gauge isn't tapped into a ported vaccum source (like one of the TB ports)? If so, move the line so it's behind the TB (tee off something that's in the manifold).

-Chuck James

[85_600]

Car would not idle with no vacuum... My experience.. a healthy 5-speed idles at 17-19in... A healthy automatic idles at 16-18 (drag from the tq)

This is good to know. In my hooking up a boost gauge post, I have a reading of 18-19 vac at idle in park and the psi never gets above 5, if that, when doing a wot ( driving of course - never at idle.) So now I have some base readings to go off of. Auto = 16 - 18. Mines a solid 18 - 19, the difference is almost exactly what my gauge is off by on the psi readings. Hmmm

back to topic ( Sorry ) :o

[TopDollar69]

I cant say 100% for sure but my Autometer boost gauge shows around 19 on the vacume side when the car is idleing. This is on a 90 Spirit ES with 5spd trans.

[85_600]

I cant say 100% for sure but my Autometer boost gauge shows around 19 on the vacume side when the car is idleing. This is on a 90 Spirit ES with 5spd trans.

So does mine - But mine also never reads over 5.5 psi even when I'm doing a WOT run. My gauge is messed up. Autometer is going to be getting it back to see what the problem is.

[85_600]

Are you sure the boost gauge isn't tapped into a ported vaccum source (like one of the TB ports)? If so, move the line so it's behind the TB (tee off something that's in the manifold).

-Chuck James

I tried this to determine if my gauge was bad or not. When I "T'd" into a TB line ( one of the ones off the back - suck through design TB ) I didn't get ANY readings at all. The needle never moved.

[turbovanman²]

I tried this to determine if my gauge was bad or not. When I "T'd" into a TB line ( one of the ones off the back - suck through design TB ) I didn't get ANY readings at all. The needle never moved.

Tee in at the brake booster, then you know for sure your getting manifold vacuum.

Basically, if your getting 16-20 inches of vacuum in any car/van, 5spd or auto, its all good.


Lee, I think you mean Total Seal rings, and yeah, I have 20-21 inches at idle-probably guage error though, :eyebrows: