Hi all,

About two weeks ago, I had a turbonetics MBC installed. I had the shop just throw it while they were in that area tapping the EGT sensor in. This particular BC likely would not have been my first choice, however, I got it for free from a buddy. During the same visit, I also had a Perrin cat-back & cat delete pipe installed. Prior to this, I had installed the HKS SSQV with recurculation myself.

The BC definitely works, (I have to set it pretty low as boost will immediately hit cutoff). I have backed it down to a level at which it spikes up to about 21 for a second or so, and then tapers off quickly & holds at about 17 till redline. My question is this:

Why doesn’t it just hold at 21? I had an Apexi EBC in my Benz, and it would hold at exactly the setting you wanted. I thought a manual would do the same (I mean it’s just a simple ball valve & spring right)? Is this tapering down effect a function of the ECU or something? It seems like it’s doing exactly what it did without the BC, except now it jumps a bit higher for a second or so, and then tapers to a bit higher boost level. I think I remember it dropping to a bit over 16 with no BC.

Anyone have any answers? Is it possible that the shop just hooked it up wrong?

TIA,
Jason

 

yeah same question here

 

When the BC was installed were the hoses connected to the boost control valve removed? ie did you take boost control away from the ECU? It sounds to me like the BC was just plumbed into the existing system, and that your boost control is still being managed by the ECU. just my 2c

 

You arent specific about how they hooked it up. But if the controller is connected to the same ports that the stock boost solenoid, the 21psi spike is just that, a spike. Its due to a surge of pressure building up before it can be bled off. The actual setting is the "Stable" boost reading you get, tapering is when that stable setting drops off slightly.

If you were to take the boost controller line from the "Snail" (the port on the turbine neck) and plug the fitting, and run that line off another accessory port like T'd off the same line that your Diverter Valve (BOV) you might find that you won't get as much spiking.

You need to verify that the taper is due to the boost controller, or the tapering is due to the BOV because its opening too early, or adjusted so it leaks boost.

A manual boost controller completely replaces the function of the factory solenoid so if its no longer connected, it will have no function. The solenoid itself should still be connected to its wiring though.

The max boost you get if you were to roll onto the throttle and build the boost slowly (avoid the spike) that is the boost level that the controller is set at.

The main reason I took out my MBC was that I would get generally stable boost at 21psi, but I would get severe spiking when downshifting now that the weather got colder.. So its no surprise.

I don't know much about the turbonetics MBC, I use a Hallman, but its possible that it also needs to be disassembled and rebuilt, the valve can be leaking, cracked, etc.. I'm not certain what would happen if it were installed backwards, but If it were a checkball valve, I would assume it would probably allow the actuator to open at its spring pressure (10.5psi)

This isn't the be-all end-all troubleshooting guide, but it should point you in the right direction.

 

what is this fuel cutoff you guys speak of?