Thread: Crankcase vacuum?

Hi all!

I picked up a 1999 Grand Prix GT about a month ago. Been going through it & fixing the little stuff, as well as doing intake gaskets & replaced the upper plenum (was starting to rot through where the coolant passages are). Did a full tune-up (plugs, wires, all filters, all fluids).

Now my problem is that the car is producing a HUGE amount of vacuum in the crankcase. If I pull the oil fill cap off (& I really have to pull), the car will die 9 times out of 10. The 1 of 10 it stumbles bad but stays running.


This is something I have yet to run into, so wanted to ask first if anyone else has had this issue. Could it be head gaskets? Or even the lower intake gaskets somehow? It runs smooth, has plenty of power & has no CELs or Codes showing up on the scanner.

I'm currently not driving it until I have time to fix it, as I don't want to make things worse, whatever the problem may be. The lower intake gasket set is the newer FelPro design (metal with molded rubber).

Sorry for the long post & thanks in advance! I'll answer any questions that may help me figure this out.

Greg.

Ok, this may sound dumb...

I can not find a pcv valve on that thing. Where SHOULD it be? The new (& old plenum) plenum doesn't have one, it's not on either valve cover, & there's none on the lower intake manifold.

Am I just being an idiot? It does happen from time to time!

Thanks,
Greg.

Damn, I feel like a moron. About 10 minutes after I asked where is it, I was going back to work & remembered it's under the pressure sensor on the left of the upper plenum.

Thanks, guys, for helping jog my memory!

Greg.