MBC question

[subiekillrGST]

Hey everyone, I just installed a ball and spring manual boost controller this weekend. It doesn't seem to be working right. I have it loosened pretty much all the way out and my boost will go to 16 psi and fall back down to 11 psi. It never stays at a constant psi, and when my car is cold the boost will jump to 17 or more psi but once it passes 15 psi it cuts out a lot and drops down to 11-12 psi. I have tried different ways on hooking the mbc up like from the turbo housing to the bottom of the mbc, and between the BOV and intake manifold. I totally disconnected the wastegate solenoid sensor. Can someone please tell me what I can do, I want my psi to stay at a constant 14 psi. I appreciate the help.

 

[oldman]

Let's do a test to see if the mbc is the problem. Bypass it by running a hose from the turbo outlet nipple and run it directly to the actuator. You should now run about 10psi. If in fact you're running 10 psi with out the mbc, either you hooked it up wrong or it's defective. If irregular boost level persists, something else like boost leak could be in play. Good luck.

 

[subiekillrGST]

thanks a lot man, i'll give it a try first thing tomorrow, and i'll post what happens.

 

[subiekillrGST]

Alright i did what you said and my boost went to a steady 12 psi. Then I hooked my MBC back up and noticed a vacuum leak, fixed that. And I capped a nipple on my intake. I screwed the MBC back down and drove it it jumped to 19 psi. So i turned it down to 15 psi, it stays there pretty steady it will drop down to about 13 psi in the higher rpm range. I also checked my spark plugs and wires, two of my spark plugs were loose so i put them back in, and now my engine doesnt cut out everything runs great. Thanks for all the help.

 

[oldman]

You're welcome. That leak you found was probably preventing correct boost singal from reaching the actuator on time, glad it worked out for you.


edit: The drop off at higher rpms is normal for a T25, I would suggest a complete leak test to make sure there are no other leaks.