WVA6

PILL PUSHER posting on my buddies computer......

I am Stage III Homebrew (see sig for mods) and last week my car started overboosting uncontrollably at WOT. It was fine last week then Wednesday I did my normal warm up and into boost and WTF, booting way past 25psi and no stopping. I thought my MBC was sticking and I picked up another boost controller from LI S4 (Thanks Mike!!) confident that the overboost would be gone and it didn't change anything, still overboosing off the charts.

If I get into boost slowly at around 7psi in 2nd gear on it will surg a bit and make a slight woo, woo, woo, (for lack of a better term)and then after that it will hold boost at 20psi (MBC in parallel setting) until the redline taper. It does this everytime in every gear???

SO far I have:
Pressure test =0
Checked all hoses=0
Lowered boost=0 (MBC is working)
Swapped out diverter valves=0
Vaged it = 0 codes

What else am I missing? It makes it very challenging to drive on the track to make sure it is holding boost before getting into it. It seems like it would be something simple since it came on overnight with no changes to anything. BTW it was running strong last Tuesday and now this. If the N75 valve was bad would it have these symptoms or would it continue to overboost uncontrollably no matter what?

Thanks guys! Stage III at VIR = Big WOOT WOOT!!

S4Dean

doesn't work, then I'd be stuck on where to turn just like you.

silva

you will only make as much boost as whichever boost controller is set the lowest. Being that you are running homebrew (likely GIAC K03 chip), I don't think there is anything wrong with your N75, especially since you mention that by turning the MBC down your boost pressure also decreases.

Have you done a visual inspection of the actuator rods for the wastegates? There is a chance that one of them may be sticking, or, that you have a small leak at the wastegate actuator hose(s).

Hope this helps.