MBC problems.

[Benag]

Ok I installed my MBC but it won't boost past 13 psi with the screw all the way in. The stock BOV holds at least around 15 pounds doesn't it?

95 GS-T

 

[andrewjscott]

your wastegate is probably jammed open slightly. I had this problem, my couldn't boost past 13 psi either, and it was slow to build boost. But man, when you fix it, it pulls hard.

 

[Benag]

How did you fix that?

 

[oldman]

Which mbc? How is it hooked up?

 

[andrewjscott]

Oldman is right, make sure it is hooked up correctly first. but if infact it is the wastegate stuck open, take the waste gate actuator arm off, and see if the flapper closes anymore (open being sorta towards the t-belt, closed toward the tranny)

 

[Benag]

I bought a PTI MBC (ball and spring) off ebay. It was $10 ( I skipped the more for quality because it fit my budget). I hooked the bottom to the wastegate and plugged the compressor housing nipple. I unplugged both from the BCS. Then I hooked the side across from the screw to a "y split" attached between the BOV line. When I unscrew it all the way I get 11 psi and all the way in I get 13 psi. Can you tell me what I did wrong or what the problem is?

 

[ddavisaf]

Yup.
You bought an ebay MBC

At what RPM do you hit 13 psi?

 

[oldman]

1. Switch the bov line back to the compressor and see if things change. If problem persists, go to 2.

2. Test run withe nothing connected to the actuator, this should result in run away boost so be sure to let off the throttle before 20psi. If in fact you get a run away boost, your $10 mbc is the problem, probably is associated to the length and tension of the spring inside the mbc. If problem persists, go to 3.

3. Make sure the flapper is closed completely. If flapper checks out, you have a dying turbo.

Good luck.

 

[Benag]

How do I make sure the flapper is closed all the way?

 

[Benag]

Well I did test 2 and it would still only boost to 13 psi. So now how do I test the wastegate?

At what RPM do you hit 13 psi?

Do you mean in first gear?

 

[oldman]

Well I did test 2 and it would still only boost to 13 psi. So now how do I test the wastegate?

If you're only able to build 13 psi with the actuator nipple Left open, nothing connected to it, this is what I would do.

1. Pull the actuator arm off the flapper, the flapper should sit tight toward the passinger side. In other words, it should take some afford to put the arm back on the lever.

2. Check for any pre O2 housing exhaust leaks, this includes any cracks on both the manifold and turbine housing.

3. Check for boost leaks by pressurizing the intake, no visual inspections.

4. If 1-3 checks out, you're most likely looking at a dying turbo.

 

[Benag]

Sorry for posting late but I've been busy. I don't want to sound like an idiot but is there something I can read on how to do this test with the wastegate flapper? I'm not sure exactly how to do it. And can I do it with the turbo still on the car?

 

[ddavisaf]

Get a line with compressed air. Like an air tank or something. Remove the vacuum source from the wastegate actuator. Hook up the air tank, and as you apply the air to the actuator, watch and see if the arm on the wastegate that connects to the flapper move. It should move immediately.

 

[andrewjscott]

If it turns out that the wastegate bracket got bent (due to a clumsy, careless brother ) the wastegate will still open if you follow ddavisaf's steps, but if its jammed partially open (like my issue) your turbo will struggle to build boost. Just remove the the cotter pin (in my case, paperclip) that holds the wastegate actuator on to the flapper and see if the flapper will close anymore.

 

[Benag]

Ok i did a boost leak test and heard the loud hissing coming from the left side of the intake manifold. Would this be enough to hold me back at 14 psi? (It now seems to be reaching 14psi in higher gears if I hold in the gas) Also, to fix this leak is it probably the gasket between the mani and the pipe? I am going to test the wastegate as soon as I get home.

 

[oldman]

Ok i did a boost leak test and heard the loud hissing coming from the left side of the intake manifold. Would this be enough to hold me back at 14 psi? I am going to test the wastegate as soon as I get home.

Yes.

Also, to fix this leak is it probably the gasket between the mani and the pipe?

What pipe? Intake manifold is connected to the TB and the intake ports on the head, no pipes.

How are you performing this leak test? Did you spray soapy water on every gaskets, couplers and vacuum hose connections. How much pressure did the system hold during your pressure test when you discover this leak at the intake manifold. Bottom line, just because you found one leak, doesn't mean it's the only one. Focus on what has been suggested so far, go through them one by one in order to eliminate them. For example, you have completly ignored this,

2. Test run withe nothing connected to the actuator, this should result in run away boost so be sure to let off the throttle before 20psi. If in fact you get a run away boost, your $10 mbc is the problem, probably is associated to the length and tension of the spring inside the mbc. If problem persists, go to 3.

and it shouldn't take days to see if the flapper is closed all the way as the checking method has been given many times, it should only take 2 mins to check.

 

[Ultimatedsm]

Ok I installed my MBC but it won't boost past 13 psi with the screw all the way in. The stock BOV holds at least around 15 pounds doesn't it?

95 GS-T

Well theres your problem why your MBC doesn't go past 13 psi. The stock 2g valve can't hold past 13 psi if its life depended on it. Get a 1g BOV or some aftermarket one that recirculates back to the intake. I am sure thats your problem right there.

Anyway, I hope that helps and good luck boosting that thing past 13psi.

 

[Benag]

Oh I thought I replied about the runaway boost test. I did that and it still only went to 13 psi. And for the leak test I made one of the devices shown on vfaq and heard the loud hissing coming from the intake manifold. Where the IC piping goes into the left side is where it sounds like it is coming from. I guess I'll get some water spray and find it exactly though. And I pulled on the flapper arm and it is really tight towards the passenger side so I guess it isn't leaking right? Well I'm going to find where exactly the leak is and fix that then post back. Oh yea, there is a small hissing coming from the bov but i guess that is to be expected. I'll have to upgrade that too.