Extremely high vacuum?

[firenexx]

I recently hooked up a vacuum gauge to my '94 Mazda B4000 (5spd, 168k). The engine was warmed up. The needle hit 30 hg (the highest reading) and didn't move. Is there anything that would cause a really high vacuum reading? I looked at a bunch of vacuum diagnosis guides but none of them said anything about it being too high.

Should I assume it's a bad gauge and go out and get a new one?

 

[cammeddrz]

improperly timed camshafts (timing set a tooth or two off) in some engines can give extremely high compression if off one way, and extremely high vacuum if off the other. i'm not saying this is the case but if the gauge is funtioning properly that is the only reason i know of that would cause high vacuum. never actually seen it to 30hg. and also vacuum gauge readings should vary a lot with even the slightest throttle change which also points to a malfuntioning gauge

 

[firenexx]

Alright. The gauge looked to me like it was trying to go somewhere above 30 but of course the needle was blocked by the pin at 30 so it couldn't.

I will replace the gauge and see what happens.

 

[disciplerocks]

My Focus pulls 20 at idle and it has a blower on it. I would think you should be pulling more.

 

[Hahnsb2]

Pretty sure 30 hg/in is a perfect vacuum, I'm sure the gauge is bad.

 

[LittleHorse]

Pretty sure 30 hg/in is a perfect vacuum, I'm sure the gauge is bad.

Atmospheric pressure is like 29.9" Hg or thereabouts, so yeah, 30" of vacuum should be outer space.

 

[BRUTUS_T_HOG]

Atmospheric pressure is like 29.9" Hg or thereabouts, so yeah, 30" of vacuum should be outer space.

0" Hg is atmospheric, 29.9" is the maximum you can get without being in space, and 30" is space

 

[LittleHorse]

0" Hg is atmospheric, 29.9" is the maximum you can get without being in space, and 30" is space

you're talking about gauge vacuum, I'm talking about absolute pressure (0" being absolute vacuum, 29.9" being atmospheric pressure).

But at any rate, an engine isn't going to produce 30" of vacuum

 

[doorgunner]

if the vacuum doesn't vary with engine rpm, maybe it's reading the manifold vacuum/+ faulty gauge......

my sbc was idling @ 25lbs. vacuum until I realized the timing was set at 0*.......LOL

 

[firenexx]

I am hooking the gauge up to the vacuum hub where most of the other vacuum lines are connected... brake booster, a/c shit, etc. Is this the correct place to check?

Also the gauge reads 12.5 in. when it's not hooked up to anything.

 

[Tedybear]

I am hooking the gauge up to the vacuum hub where most of the other vacuum lines are connected... brake booster, a/c shit, etc. Is this the correct place to check?

Also the gauge reads 12.5 in. when it's not hooked up to anything.

Gauge is screwed. If it's not hooked up to anything? Shouldn't be reading anything LOL.

It happens, sometimes tools get dropped and the internal workings get damaged. It's well worth it to pick up another one and redo the tests.

S-

 

[Big Jim M]

30-12.5=17.5... About right I'm think'n.
Big JIm

 

[cammeddrz]

i went out an started my v8 bII and revved it, the most vacuum i saw on the gauge was as it was revving down and it hit around 22

 

[AllanD]

that guage is phucked.

Get another.

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