Vaccuum problem

[James Czebiniak]

Need some input with a vaccuum problem. Will try to keep this short.
RebBuilt an 89GT 5.0 bored .030, b cam, new lifters, comp cams 1.7 roller rockers, new stock heads slightly exhaust ported.
put engine together. Had a major vaccuum leak and it ran terrible. Once I found the leak (forgot to plug in PCV valve) it smoothed out and idled fine.
was sent a bad set of FMS lifters from Summit. Had to remove upper and lower intake. Got new lifters, put it back together and it runs like it has the leak again except this time all vaccuum lines are connected correctly.
I get almost no vaccuum at idle. It idles like it has a major lift cam with about 20 degrees overlap. Burns a lot of fuel because the computer cannot figure out what is going on. I have had 4 guys look at it and listen and no one can find a leak.
If you speed up engine to about 1500 rpm you start getting vaccuum.

pulled off upper intake again and the gasket looks fine. No loose hoses no obvious leaks.

Anyone have any advice on this.
Feel free to email [email protected]

 

[ss93cobra]

I know this doesn't help much, but if you had a vacuum issue that you corrected by installing the pcv valve, tore it down, and now have the same problem, the first place I'd look is with what you've done. Double check all the lines and fittings that are involved in the intake removal to find your problem. I'm not trying to sound like a smart ass so please don't take offense. If it was great before you touched it, it has to be something you've done. Your cam specs and lifters should be a decent streetable combo.
Good luck.

 

[DMAN302]

Check the PCV grommet a poor seal there is a vac leak. Also did you get the grounds all back...including the hego (spelling) orange ground wire often tied to a intake bolt. That ground is for the O2 sensors and can cause issues.