Maybe your particular MBC unit is funky. Have you tried swapping in a known "good" MBC from a buddy's Evo? Also, when you say that you disconnected the MBC and tested the WGA, what exactly do you mean? Did you disconnect the MBC and then run a line directly fron the turbo's compressor housing discharge nipple to the WGA nipple?

 

Did you already put your MBC directly in-between the turbo nipple and wastegate?

 

maybe u should take the mbc apart and clean it for good measure.. maybe ur ceramic/steel ball is getting stuck on occasion

 

could be a hole in the diaphragm of the WGA.

 

Yeah, I kinda think that he should try disconnecting the MBC. Then running a line from the turbo's compressor housing discharge tube nipple, directly to the wastegate actuator nipple and then set boost up to 17 PSI by adjusting the length of the threaded waste gate actuator rod. Then reinstall the MBC, and adjust the final 4 PSI of boost, up to 21# with the MBC.

 

where did it say what type of MBC it is?

if it is a hallman, check which nipple on the hallman has the tiny pin hole out of the base of the nipple where it threads into the body of the MBC. the nipple with the pin hole must be on the side port of the body, not the bottom. this will cause the car to spike and drop. i've seen it before... any likely is a result of someone taking off the nipples to service the MBC, but putting them back on incorrectly.

 

By disconnecting I meant having the WGA completely disconnected with no vacuum line attached and slowly attempting to build boost past ~12psi. I believe that I read this in a seemingly similar thread about ~12 boost limit, but I do not know exactly what the test shows. It seemed that this is where the previous thread left off and I wanted to be able to have the information about disconnecting the WGA before starting a new post because I believed that my symptoms were similar.

Would a hole in the diaphram exhibit similar symptoms? I have not tried substituting nor cleaning the MBC controller. It is new and it does elicit a change in the boost spike psi when adjusted. Is the wastegate adjustment a necessary step with a MBC or would that be a workaround; I will give this a try later tonight. Also, I have not yet performed a boost leak test; is this still applicable? I am planning on acquiring the necessary pieces this afternoon for the boost leak tester.

 

It is the Buschur Racing MBC from their stage 1 kit. Is this a hallman type MBC? The description sounds similar. Is the pin hole in the nipple applicable to the Buschur Racing MBC design as well?

 

I picked up the parts for my boost leak tester but do not have time tonight to test the car since I have been driving around; I will do so tomorrow morning. I did disconnect the WGA and put pressure it's line to test for leaks; it held at ~20 psi with the arm extended for about 2 min until I disconnected it. Is this an appropriate way to test for a leak in the diaphragm in WGA? I do now have my tactrix (sp?) cable; is there any datalogging that I could perform and then post to help diagnose this problem? If so, which parameters should I attempt to log?

 

I completed the assembly of my boost leak tester and finally got around to testing earlier this evening. I first isolated the intercooler section by plugging the outlet pipe that goes into the UICP; it is here that I noticed some weird results.

The system held boost well; the only slight leak that I could hear was coming from my boost leak tester. The leak only amounted to ~2-3psi over ~5 min. The MBC was connected between the turbo outlet and the WGA and exhibited no audible leaks. I then noticed that the wastegate arm was extended at the ~15psi level where I stopped. I then depressurized and turned the MBC to its highest setting; I stopped at less than ~20psi and the wastegate arm was extended. Repeating a third time, I noticed that the wastegate arm began to extend at ~12psi.







The MBC is connected correctly: the line from the turbo outlet is going into the bottom of the MBC (farthest from the knob), the line to the wastegate is comming from the top of the MBC (closest to knob). The only spring that it came with is in the body of the MBC. Is my MBC not holding any pressure? Is it a defective piece, or could this be rectified with a rebuild? It is new with my BR stage 1 kit that I received less than two weeks ago. What does this mean?

 

no boost leaks... hmm i suspect it is the MBC. find a friend with a hallman or forge and give it a try. still wondering in that buschur MBC has the tiny pinhole on the WGA nipple side of the ball (if it is a ball and spring type)...

 

Does the MBC have a very small bleed vent in the body? If not, that could be your problem

 

I could not find a pinhole on either nipple that goes into the body of the MBC nor could I locate a vent hole in the body of the MBC itself. It will be a while before I can swap it with another unit as I do not even know anyone with a turbocharged car, let alone a MBC. I think this, along with the MBC being a new part, led me to eliminate all other possibilites before testing the MBC itself. Is this a problem with the unit itself? Does anyone else run the Buschur MBC?

 

I guess that you didn't like my idea. To eliminate the MBC as a possible culprit, first disconnect it. Run a hose directly from the turbo's compressor discharge tube nipple to the WGA nipple. Now, you can set boost mechanically, the old fashioned way by adjusting(either lengthening or shortening) the threaded wastegate actuator rod until you reach your desired boost level. If boost holds steady with this method, then your problem is either the MBC itself or a faulty hose connection.

 

Yes, I was apprehensive about your idea. It was not because I did not "like" it, but because I felt that I lacked sufficent knowledge to give it a try. From my forum reading: I was unaware of others having to adjust their wastegate to install a MBC, there were threads reporting shortened life when setting the WGA to a higher psi, I did not want to have to wait through several heat cycles to adjust the boost and continually disassemble the car without eliminating other variables first. There were suggestions that my diaphragm may have a leak and I wanted to test this before adjusting the wastegate. I asked further questions about this procedure that were unanswered. Based upon my knowledge at the time, the wastegate adjustment seemed like a workaround to the problem instead of addressing the possible real issue at hand. I felt there were simpler ways for me to test the system and the MBC without adjusting the wastegate.