I'm having over boost problems.

[Splitpi]

I have a boost gauge installed and a PTI ball and spring MBC. The MBC is setup like this:

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The setup was working great and dialed in right around 13 psi. I got around to installing my Brode UIC and 1G BOV and then all kinds of things happened. My first test drive I hit nearly 22 psi and quickly let off the gas because it freaked me out. I have since been trying to adjust it, but I don't seem to be having much luck. I have the adjuster screw out as far as possible and I'm still running higher boost. In first gear it cuts short to about 10 psi, then in second it hits 17 or so and holds about there for the rest of the gears. Is my spring worn? Or is there something wrong? Perhaps a vacuum leak after switching the tubing from the stock 2G BOV to the 1G (prior the T fitting was JB welded directly the BOV nipple, I put a new T fitting in along with tubing)? Also does the size of all 3 outlets on the T matter, i.e. can they all be the same size with no problems? I also yesterday replaced the tubing with silicone from the Larson Kit by Road Race. Didn't seem to help much. Any suggestions? I hate having to drive with one eye on the boost guage and the other on the road to make sure I don't over boost. Its my daily driver and baby so I don't want to kill the car.

Also don't know if this is important or not, but when I bought the car, it was stock except for the MBC and boost guage. But the BCS was disconnected. Its my understanding the BCS is not used when using an MBC, is that correct?

 

[oldman]

1. Turn the mbc all the way down and see what happens, sealing your leaky 2g bov by replacing it with a 1g will change the boost level.

2. Perform a leak test, this should always be included in any work done involving the intake tract.

3. Switch the pressure source from the BOV line back to your compressor housing and mount your mbc where you will be able to run the shortest hose routes possible.

4.

Also don't know if this is important or not, but when I bought the car, it was stock except for the MBC and boost guage. But the BCS was disconnected. Its my understanding the BCS is not used when using an MBC, is that correct?

That is correct but you have to leave it plugged in and cap of the nipple on the intake pipe that use to connect to the bcs.

5. Once you have done all this and fix all leaks, you will know have there are other problems or just the typical T25 characteristics.

 

[Splitpi]

3. Switch the pressure source from the BOV line back to your compressor housing and mount your mbc where you will be able to run the shortest hose routes possible.

Well with what the MBC was set at, I switched the positive side (inlet) to the Compressor nipple. I also shortened lines and zip tied it to the intake pipe so it is still accessable. I took it for a test run. 1st Gear it surged to about 6 psi. 2nd+ Gears it surged to 15 psi then held at 13 psi. Is it normal for it to spike so much? I just don't remember it doing that before when I had the stock UIC with stock 2g BOV.

 

[oldman]

Well with what the MBC was set at, I switched the positive side (inlet) to the Compressor nipple. I also shortened lines and zip tied it to the intake pipe so it is still accessable. I took it for a test run. 1st Gear it surged to about 6 psi. 2nd+ Gears it surged to 15 psi then held at 13 psi. Is it normal for it to spike so much? I just don't remember it doing that before when I had the stock UIC with stock 2g BOV.

Yes, a typical T25 will spike about 2-3psi before it settles, all this was probably covered up by your leaky stock 2G BOV. Don't be lazy and go through the leak test anyway, it will only improve the situation. The huge difference in boost level between tapping the compressor vs. the BOV line is a clear indication that you have leaks some where in between.