bureau_c

After adding a catback (car already had dp, intake, mild streetport) I noticed my boost getting a bit out of control, so I decided the stock boost control wasn't cutting it and added something like Damian's dual ball-and-spring MBC setup. Basically, I've replaced both pills with ball-and-spring valves and then bypassed the stock solenoids altogether. However, with both valves wide open (i.e. lowest possible boost) I'm seeing primary boost that is basically uncontrollable, hitting 14-15 psi before I let off. I can't say what kind of transition spike I'm getting because I'm too chicken to keep my foot in it with those levels, however if I removed or blocked the lines going to the wastegate and prectontrol actuators entirely, I imagine it would act like this (oddly enough, if I get my rpms up over 4500 and then gun it, so I'm in twin mode, boost seems to hold around 10 psi...so the wastegate must be working then). Basically, I'm at a loss, so if anyone has any ideas of things for me to check, fire away...I'm all ears!

jds

PS: Yes I searched...most primary boost problems are underboost situations, and the few overboost issues I found were not accompanied with solutions.

DamonB

Overboost problems on the primary are typically because the precontrol is not functioning. Since the precontrol does not vent any boost to the secondary, you overboost on the primary. I had this issue first hand when my precontrol solenoid went kaput.

bureau_c

That makes sense. Now, since I've bypassed the solenoid entirely then assuming the line to the actuator is intact (it is) and assuming the valve I put in place of the pill is not broken (I would think its unlikely but its on my list of things to verify) then I must have an actuator problem? Can you think of anything else that it could be?

jds

DamonB

If everything was fine before you installed the valves, I don't believe the actuator has failed all of the sudden. Something in the way you hooked everything up is probably wrong. I am not familier with Damian's setup but I would triple check everything. What happens to the lines that lead to and away from the precontrol actuator? In stock form the solenoid is after the actuator.

bureau_c

I don't think things were fine before I made the change, although they do seem worse now...however I think I was misinterpreting some of my boost problems prior to the change and attributing them to a more wide open exhaust rather than to something failing.

In my current configuration I've unplugged the line going to the inputs and outputsof both wastegate and precontrol solenoids and plugged them together (actually taken the line to the input and plugging it onto the little manifold thing where the output from the solenoid went...essentially bypassing the solenoids. Then the valves go where the pills used to be. This configuration was used in Damian's initial setup...I think he has changed some things around a bit since then, although I'm not clear why, as everything seems to be working fine for him in either config.

jds