Map vacuum source.

[myburb]

This question is regarding map connection on gm 7.4. Early 90's they connected to a source on the throttle body, 93 they had it connected to #8 runner and 94 they connected to both #8 and #7 runners. I expect the 8&7 were to smooth the pulse but I was wondering why they moved from the throttle body. My after market intake only has an outlet on #8 and the pulse is really jumpy. To the point I thought maybe there was a problem with the motor. I connected to a source on the throttle body and the gauge is super steady but it doesn't idle as well. I haven't done a ve redo but just wondered if there was a reason I am missing why it was moved from throttle body to runner.

[1project2many]

I read this and thought "I don't remember MAP being connected to the manifold." So I looked up vacuum diagrams. The diagrams coming up for various C/K trucks w/ 7.4 in 93 and 94 show MAP connected to the rear port on the TB. That's what I remember from my dealership days, too. I'm not promising that the diagrams they provide are correct for all models but GM usually connects MAP to a port that provides a signal from both halves of the dual plane intake.

Edit: Best picture I've found is this link.

[myburb]

On the rockauto diagrams they show a 95 7.4 with isolated ports the same as my 94. Being as there were so many others off the throttle body that worked ok I will go that route. It makes the vacuum gauge and the data stream map reading so much smoother.