Vacuum Gauge Question

[MMJAXSTANG]

Hello all,

I just installed an Autometer Vacuum gauge and I want to make sure I have it installed correctly. When I have the throttle wide open the gauge reads 0. It seems like it should be the other way around. At idle, it's around 15 which is right. Do it have something backwards or would it not work at all if the tubing wasn't installed properly?

 

[Superhereaux]

your car should have 0 vacuum at wot




sounds like you got it right

 

[Mike97gt]

yep that is right

 

[hotmustang331]

Ok, here is how it works.

You have a vaccum line BEHIND the TB plade...now the engine is running but no air is coming through the blade. The IAC is controlling the air based off of EEC imput and it is also measuring vaccum I believe. That means the other ports are also under vaccum (15 inches)...but only the ports behind the TB, not the lines into the CAI which is before the TB.

NOW, when you go WOT that TB blade opens FULLY up, and the motor is pulling in all the air it can handle since it has a BIG source of free flowing air. Now its not going to try and "draw" air through that little hole and pull a vaccum when it has a big open source of free flowing air.

Basically like taking a sealed can, drill 2 holes in it the size of a straw. Put a straw in one hole and leave the other open. Now suck on the straw...whats going to happen? NOTHING, you will just fill up your loungs. Next to NO vaccum in the can since it already has a hole and the slight low pressure just draws in more air. If you were to plug the hole (TB closed) and drill a VERY small hole (IAC) then suck. You can pull a nice vaccum and slowly keep sucking in...and you can hold that vaccum. Understand? lol (I know long )

 

[John Smith]

How much vacuum should the car pull at idle? My car is pulling a little bit over 20.

 

[jeffnoel]

I just picked up a Vacuum gauge, were's a good place to get a strong signal. Can you post pics were you installed the Tee?