Here is the setup. Its a Greddy Profec B Spec II. Everything is Greddy OEM parts minus the harness that controls the solenoid. Now the problem. The car SEEMED to be working fine. 8psi all the time, no problems whatsever.

I put on some T-Bolt clamps in place of my worm drive clamps. Nothing major. I noticed a week or so BEFORE I put the clamps on that vac showed "-99" on the Greddy at idle. The boost gauge showed me -21. Now, I will note that the boost gauge and the Greddy unit both get thier signal from the same port on the manifold. The actual vac/boost to the solenoid is on its own seperate port. The line is a small nipple with an adapter to a larger hose.

So anyways, I notice a drop in vac on both the Greddy and on the boost gauge at idle. Goes down to like -19 on the gauge and usually like -94 on the Greddy. Nothing large I assumed.... only now it would boost 10psi for like 2 seconds, the it would shoot to 12psi and hold. Whatever, seemed cool, car was fast, trapping 105mph, all was good. I didn't think too much of it at this point. Few weeks go by, everything is golden, 10psi then it hits 12psi but its working wonderfully otherwise. I get on the highway one day and notice its quite a bit slower, I look down, gauge only shows 8psi now under boost. 1st gear, 2nd gear, 3rd gear, it doesn't matter... 8psi. Nothing more. So I was thinking, perhaps the solenoid isn't working correctly... Up the boost on the Greddy unit and it responds. Dialed it in to where it hit 12psi in every gear, wrote the problem off... Then I go home from work and now it wants to boost like mad. I hit boost cut at 14psi in every gear... damn thing is acting up again. I dial the boost controller down, now its doing the 10psi for a few seconds then to 12 crap again.

Anyways, its back to holding 8psi now, I don't know what the deal is. I was hoping someone had some insight as to when I could look for or why its doing this. Whenever its boosting lower, I am noticing the vac at idle is also lower. When its going to boost higher, I am pulling more vac at idle. The car seems to run fine otherwise, was trapping 105mph at the 10-12 setting, so it seems to be healthy. Leakdown and compression are good also, no change since last tested a couple thousand miles ago. Any ideas?

 

check your vacum lines for any kinks/melting. if you have zip ties on them, they could possibly be the culprit (not where they meet the fitting, but where you used zip ties to hold the hose)

 

I've gone as far as putting in all new lines. The only thing I have to work with right now is that POSSILBY the size of the line going to the solenoid itself is too small. The nipple is like 3/8", but I have it reduced down to a very small vac line to tap off the back of the manifold. Perhaps this would cause problems? Not sure how since it works sometimes, then not others, but its just a thought. There are no kinks that I can see in the system.