The car is up and running . It idles at 400rpm when warm . The vacuum is at -4.5in. Ive checked for leaks and cant find any . The car runs great [ havent taken it over 4,000rpm ] Are the cams responsible for the low vacuum ?
Im going to take it in and have them bump up the idle . Will this improve the vacuum ?
Others have told me and I do now remember running around -19in of vacuum before the cam and rebuild

 

Mods can delete this post...found my answer....cams will effect idle and vacuum

 

i have the JWT cams and i idle low as helll...when starting up cold, car sometimes just shuts off

 

yup..raise the idle. also, if you installed a lightened flywheel, that could lower your idle as well.

 

I knew it would lower the idle , but I didnt think it would have that much of a effect on the vacuum

 

Oh....also...your lower compression pistons mean less vaccum..as well....IIRC.

 

If you turn on your AC/defroster, the idle should bump up and vaccum should increase. This simple test will tell you that an idle bump is in order.

 

Idle is bumped up to 750 rpm now . Still a little ruff , but vacuum iss up to 6.5 at idle now...thanks guys

 

you HAVE to do the idle air volume learning procedure. I bet it will correct the problem. Have you done it?

 

Yes I did have them do it. But I think they did it before they upped the idle and I wasnt done scaling the injectors back all the way . The dealers tech guy knows poop about this ECU . At first he called me and said they couldnt up the idle , that it was set . I had to tell them to keep looking for it in Assist , that 100's of guys have done it . Im going back to have them run it again when Im done . Cold as hell , and I dont get much time running the car right now

 

booger.....

they MAY be right on not being able to set the idle. If you have an 04 car that is of ULEV2 variety, you cannot set the idle (from what I heard).

 

Sorry to bring this post back from the dead but I noticed today after finally installing my ST my vacuum was -6.0mm hg and with it idling around 900-950rpm. I dont remember it looking like this before. I do have a built motor with nismo cams. I'm getting a little worry about this.

 

I have a Forged Performance stage 1 short block with Brian Crower stage 3 Cams and pull 14"@900 RPM.

 

isnt -6 at idle a little low? even with cams?... mine is at -21. but then again i dont have cams so..

 

Here's the thing, i'm getting my readings off the HKS VPRO intake manifold sensor. Is that reading suppose to match up with say a boost gauge reading?

 

make sure you are all reading the same units. mm HG doesn't equal inches of vacuum.

 

ON the camp 2 display, it's showing -6 psi from the vpro intake manifold pressure.

 

Units of measure are getting mixed up here. -10 inch/m is same as -5psi. -20inch equals -10psi.

Expect lower vacuum with cams and a built motor. Less compression and longer durations/lift will decrease vacuum at idle.

 

thanks for clearing that up. Is -6psi normal then?

I'm thinking it should be okay -6psi = 12.22 in hg

 

Yes, it's within the normal range I would expect for a built cam'ed engine.

One other thing you may consider is having a smoke test done. It makes finding small vaccum likes incredibly easy and thorough. No more listening for air. We smoke almost every car that comes through here, if the customer reports any type of idle/vaccum/startup issue. 9/10 times we find a small leak. Smoke machines aren't cheap, but they are a valuable diag tool.