Vacuum Question

WhiteDevil · Aug 31, 2005

Well even though with the tweecer my car has run bomb for about 6 months, for some reason my idle quality has started to decline. I got a new IAC and put it on there, but the problem still seems to be there, it surges every once in a while now and dies some times too. I was no wanting to see if ican check my vacuum. I have seen people talk about measuring inches of vacuum. Is there like a cheap gauge or something i can get at kragen or autozone to check to see my vacuum and what kinda inches im pulling. Also if i can get something like that what is a good vacuum for a cammed 5.0? Thanks guys.

HISSIN50 · Aug 31, 2005

One can use a cheap vac gauge. However, I recommend using a Miti-vac. It works for this purpose and also can be used for tons of other purposes (brakes, removing fluid via fill holes, testing vac lines individually, getting your vacuum controlled hot-tub jets to change jet settings when the controller craps out , etc). Your choice though really with which you use. A cheapo vac gauge would work fine too.

A stock 5.0 will pull about 20" hg at idle. With your cam, I will defer to others. But if you saw under ~13" hg, I would look further - most EFI cams with power brakes, etc, dont have that low of a vac signal.

I would note that generally a vac leak will cause a hanging idle and a higher than normal idle. In my experience, it has not caused stalling.

I take it that there are no codes? As a very likely unrelated aside, a hanging (open) EGR can cause some surging and stalling. You might not even have EGR anymore.

Good luck bud.

DarkProphet · Aug 31, 2005

I use my boost gauge to measure mine, doubt ud want to buy one of those as they are like 50 bucks.

When you say 20" of hg, are you talking at 1000rpm or 800? or what? Thanks!

FlyBy763 · Aug 31, 2005

My car usually makes 19-20" Hg at idle...It made that much when it was idling at 550 and when I turned it up to 800.

WhiteDevil · Aug 31, 2005

Ok do you think these vacuum gauges are something i can get at like autozone or kragen on my way home from work today?

HISSIN50 · Aug 31, 2005

DarkProphet said:
When you say 20" of hg, are you talking at 1000rpm or 800? or what? Thanks!

Flyby hit it. It does not have much to do with what your actual idle is (though we are talking base idle with a closed TB). The TB butterfly restriction is what helps to create vac, so base idle does not matter much. As soon as the TB starts opening, the vac starts to diminish.

John, you should be able to get an interior (permanant) vac gauge, a Miti-vac or a diagnostic vac gauge at the parts store.

Good luck.

CManT1914 · Aug 31, 2005

HISSIN50 said:
Flyby hit it. It does not have much to do with what your actual idle is (though we are talking base idle with a closed TB). The TB butterfly restriction is what helps to create vac, so base idle does not matter much. As soon as the TB starts opening, the vac starts to diminish.

John, you should be able to get an interior (permanant) vac gauge, a Miti-vac or a diagnostic vac gauge at the parts store.

Good luck.

Yep, any parts stores that carry fuel pressure gauges, compression gauges etc. should have vacuum gauges.

JT, did somebody change your avatar again? Now it flashes, lol.

HISSIN50 · Aug 31, 2005

CManT1914 said:
JT, did somebody change your avatar again? Now it flashes, lol.

Yeah, Daggs was busy calling in favors to have a guy on here make mine do things.
The kicker is that for some reason I cant see what the movement is.

CManT1914 · Aug 31, 2005

HISSIN50 said:
Yeah, Daggs was busy calling in favors to have a guy on here make mine do things.
The kicker is that for some reason I cant see what the movement is.

You can't see it? The crystal ball glows.

WhiteDevil · Aug 31, 2005

Luckily i decided to call my dad and ask him if he had one before i bought one. He was like yeah in the bottom drawer of the tool chest. So i grabbed it, looked pretty damn old late 80s probably. But i hooked it up and it was reading about 15 or 16 so i guess its good in that area.

Zero Signal · Aug 31, 2005

That should be ok. I usually read about 17, but I also have busted vacuum lines that are taped together.

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