The truck is in my sig. I have installed a Comp Cams 35-255-5 camshaft and it has a KN FIPK and the air pump and associated plumbing is removed. I am wondering what kind of idle vacuum I should expect? It seems a bit low to me, around 16 in. hg. at idle and it wavers slightly with a corresponding speed change.
It is speed density EFI.
Thanks

 

i think it's something like 17 to 21 in.hg

 

Doesn't sound bad to me, but you are probably getting close to the limits of the SD system at idle. If you think it's an issue, you might want to try an adjustable fuel pressure regulator and bump the pressure a couple of PSI.

Also, has the engine been rebuilt? An engine will gradually lose vacuum as the rings wear, so you might have to factor that into the mix.

 

Manifold vacuum is dirctly related to the camshaft. Your aftermarket cam will not pull the same as the stock cam.

 

That cam is a SD EFI compatible cam that has been recommended here many times, I was hoping it would not cause issues with the stock ECM. The engine is rebuilt less than 4k miles ago.
Thanks for the comments, guys