This weekend I added a dual guage pod with a vacuum guage and air/fuel guage.

1988 305 TBI 700r4

FYI: Both are just toys to me.

Here's my question. I did a quick trace of vacuum lines and I decided to hook into a line that came out from the manifold and routed along the firewall over to the drivers side and down to near the front fender. I think that is the canister that stores gas vapors. My reasoning was that any vacuum line should serve my purpose. I was wrong. The guage works great. The trouble is that it appears to be measuring the vacuum in the tank. I didn't even know there was a tank on the car for holding vacuum.

I was trying to avoid routing a vacuum hose from the manifold over to my firewall. That is why I chose this hose. Now I'm wondering where the best place to hook in is. I've lost a little confidence in finding an appropriate spot.

This all boils down to 2 questions about my vacuum guage.
1) What did I actually hook into?
2) where is the best place to hook into?

BTW: I did do a search. there are a lot of posts about vacuum but not vacuum guages and none on where they hooked 'em up.

 

depends on what you want to see.

if you want to see the real time manifold vacuum, tap into any line that goes into the manifold BEFORE it goes thru a one way valve.

the only line you dont want to tap anything from is the MAP sensor line... any of the other lines would be just fine.

 

Thanks MrDude.

I was wanting to see real time manifold pressure.

Where does one get a vacuum line drawing? Is this something that is in my factory service manual (FSM) but I just can't find it?

 

theres usually a sticker under the hood.

but you could just look at one of the nipple connections going from the manifold, and tap into it there.

 

It never dawned on me to look under hood for the vacuum line mapping.

I did a closer trace of the hose I cut into after the vacuum guage showed a rather constant 21 to 24. So I've seen my options. My lesson learned is "always remove the aircleaner completely so you can see everything hidden under it". Doing that may not have helped me since I didn't know what the big fat T did. Only after this mistake did I find out I had a vacuum tank.

I'm also wondering (since I have the data) if the value I'm seeing from this location a good value.

Thanks again MrDude!

hopefully some newbie in my shoes can know find this if they guess the correct search words.