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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: chevyguy5894 on November 25, 2007, 01:45:26 pm

Title: Vacuum
Post by: chevyguy5894 on November 25, 2007, 01:45:26 pm

I hooked up a vacuum gauge the other day on my truck and it read 0 at idle and about 50 from 1500rpms and up. I was wanting to know what I sould be looking for for vacuum. I dont have a book that talks about vacuum. Its a 350 with heads and cam with holley projection on top. Just curious what other people say before i find a book or read the holley manual again.

Title: Re: Vacuum
Post by: VileZambonie on November 25, 2007, 03:48:33 pm

Did you hook it up to ported vacuum? You need to install the gauge to a manifold vacuum source.

http://forum.73-87chevytrucks.com/smforum/index.php?topic=5963.0

Title: Re: Vacuum
Post by: chevyguy5894 on November 25, 2007, 11:20:16 pm

(http://i100.photobucket.com/albums/m24/chevyguy5894/947c_1.jpg)

I took a reading off the two on each side but not the two in the middle. Also is that diagram for the motor being at idle or a certain rpm?

Title: Re: Vacuum
Post by: chevyguy5894 on November 25, 2007, 11:23:03 pm

I forget to add as you are looking at this pic the furthest one on the left is where my tranny is hooked up the one on top in the middle is pcv and the rest are blocked.

Title: Re: Vacuum
Post by: VileZambonie on November 26, 2007, 04:23:08 pm

There should be suction there with the engine idling otherwise it's ported vacuum which you would probably only use for EGR or perhaps Vac advance if you have it set that way.

Title: Re: Vacuum
Post by: chevyguy5894 on December 03, 2007, 06:52:26 pm

I figured it out. The projection had a port on the back that was the manifold vacuum. It was reading about 33 to 35. I had to set the ecm and was able to get it halfway set.  Thanks Vile.