So I had an overboosting issue where it seemed the ambient temperature affecting my boost way to much or my boost threshold was very fine or something like that (so I turned it down a bit (17 psi or so, with taper from the leak). I went to CBRD, got a boost leak and everything plugged up and now it goes to 17 psi and holds strong till redline

So I now that I know all my boost leaks are sealed I figured I'd inch the boost up to 19-20 (where it is supposed to be and leave it) but when I went to go do some pulls and inch up the boost, no matter how much I turned the FORGE MBC up, the gauge read 17 strong. I turned it up probably close to 3 full rotations and about 9-10 clicks and nothing is happening so I don't want to turn it up any higher

Bad MBC? Looking for some help please

 

Hmmm.

 

Where was it leaking from anyway?

 

So, what happens when you turn the adjustment knob on the MBC all the way back out to what should be the lowest boost level attainable? Does the boost level still stay at 17#?

 

yea, try doing what the above guy said. if it stays where its at. its gotta be the controller

 

You did the right thing: First you went to CBRD and got a verified and expert boost leak test run on your car at their shop. So, we are now assured that a boost leak is not the cause of your boost level not responding to your turning the adjustment knob on your MBC.

Still there are a couple of things that we should further assure ourselves that are not funky with your setup. It may very well be that as you suspect there is something wrong with your MBC such as a sticky ball, etc. So, you can disassemble the MBC(Hallman, right?) and inspect for free movement, lubricate and reassemble the unit.

Whenever I experience a problem such as the one you describe, I always like to go out and buy a couple feet of new vacuum hose and replace the old existing hoses with new stuff and secure the hose ends with hose clamps to their respective ports or nipples.This way we are now sure that it is not a boost hose problem. I realize that this seems redundant but rubber hose is so cheap and I like assuring myself of proper hose integrity, connections, fitment and routing.

If you disassemble and lubricate the MBC mechanism then we also know that it is not the MBC that is causing the problem. Note: If you still suspect the MBC, it is really easy to verify its functionality by replacing it with another MBC...... That simple.

When CBRD ran the boost leak test did they tell you at what PSI the diverter valve was lifting? Did they tell you up to what PSI level they pressurized the intake system? If you get a chance, ask them. I'd like to know.

Once we eliminate faulty boost hose routing, faulty MBC function, boost leaks, and premature DV venting, then we get down to my favorite area which involves the wastegate and the wastegate actuator's possible role in this scenario.

EDIT: Incidentally, I'd like to know more about how the car was running before the boost leak test. Were you running at a boost level higher than 17# before? Were you experiencing boost taper? You sort of imply these things but some more details as to how the car was actually running before you began to experience the problem might be helpful. Also, what DV and WGA are you currently using?

 

we have seen quite a few forge mbc's (well forge products in general, especially their actuators) cause problems-

let us know what you find out-

cb

 

I'll switch all my vacuum hoses when it gets nice out again.

Yes I was running a boost level higher than 17 BEFORE the test. BEFORE the test is when I had a overboosting issue. I turned the boost up to 19-20ish and then if it was really cold outside the boost would spike to 23 and it would overboost, fuel cut and throw a CEL.

There was boost taper, from 20-about 16-17 (where it is now)

I'm running a Evo 9 BoV (bought used)
Stock everything else.

It's a forge MBC by the way, I think I'm gonna just go ahead and buy a hallaman pro cause I've heard nothing but great things.

 

As Chad says the Forge MBC's are a great looking piece of aluminum. However, over the years several users have complained about experiencing functionaliy problems with them.

In the winter months on cold nights you can expect a 2-4 PSI jump up in boost level. That is normal with an MBC equipped car. With an EBC, or with ECU boost controlled boost you won't get that variance. So, that is just the nature of the beast(MBC).

The taper is normal too with a stock 16G turbo especially if the turbine housing is unported. You can reduce taper by porting the housing and by using a couple other tricks. It can be reduced and even eliminated in some cases.

So, you are experiencing several problems that have to be addressed one at a time. These problems have all come together at the same time. But, they are not really all one and the same.

 

It's not really that cold outside is it? I mean you can still tinker with your car a bit in spite of the nippy weather can't you?

If it is not too much trouble, I would like you to do what I asked you to do before and rotate your MBC all the way out counterclockwise to the lowest knob adjustment possible. This will tell us two things which I'd like to know:

1) Is your MBC really stuck on 17# or is it reponsive to being adjusted lower than that level.

2) We will get a good idea of the actuator spring pressure your gate is running at.

So, turn the knob all the way out counterclockwise to full-soft and do a WOT run in 4th gear for me. Report back what boost level you see on the gauge.

 

I am pretty much sure that your problemo is related to too little WG spring tension. Before with the boost leak it was not a factor. Once you got the boost leak fixed then it became a problem.

I think that if you run the test which I asked you to above(turn MBC knob all the way out counterclockwise) you will get a very low boost reading of 11-12 PSI. That is your Gate is not preloaded at all.

Since the boost leak was fixed now your WGA diaphragm is forcing the spring to open the flapper valve at much lower shaft speeds. I am still tninking this through and I'll explain it to you later as the day progresses from my iphone. (Gotta run!).

Basically you need to increase preload on the gate. There is nothing wrong with your MBC per se. It will be brought back into play(range of adjustment) once you increase WG spring pressure.

 

Sometimes in a case like the OP's there is not one easy isolated single cause or a single and simple solution. There are cases where there are several contributing factors. No one single cause. Everthing being a little bit off and having all those little things add up is what I am thinking here.

So, he needs to isolate possible causes and eliminate them one by one. First, he did the boost leak test. That was number one on the list. We can scratch boost leaks off the list of possibilities.

Next he should look at whether or not his Forge MBC is functioning properly. There are a couple of ways that I know of to troubleshoot the MBC. First, would be to unplug it and substitute a known working MBC in its place.

The second method is to unplug the MBC and try raising boost up to the target boost level(22 PSI?) by rotating the turnbuckle on the end of the actuator rod.

Also, i would take a look at the DV. Probably I would crush it a little bit.

Like I mentioned he started fine and did the boost leak test. Now he just needs to systematically go through the other possibilities one by one. I realize that it is drudgery. But, someone has got to do it.

 

take the mbc off all the way take the ball and spring out and un screw the bolt out that is inside and clean it off a little and put it back and then go try it..... i had same problem thats how i fixed it..

 

^Not a bad idea

 

Okay so, turned the mbc down all the way (12.5) rotations. Boost is at 11-12 ish. Gonna try and take my mbc apart or is my Wg messed up?