MBC not working?

[GSTdude06]

I just bought a mbc and boost gauge and got them both hooked up exactly how it said. And it is turned all the way down but it says it is still boosting at 15-20psi on a T25 turbo. What would cause that? When it gets that high the car doesn't boost correctly. I don't know whats going on and any help I will thank.

 

[FastGS-T]

did you drive it with just the boost gauge installed first to make sure you were hitting 10 psi?

then when u installed the mbc, did you make sure the side with the bleeder hole was the one going to the wastegate?

if your mbc was an ebay knockoff it might be set at a 15psi minimum like mine is ( i added a larger/stronger spring to my slowboy one)

 

[eclipsh]

Double check all your hoses too and make sure you don't have one pinched off.

Also, explain exactly how you have it hooked up. It may be bad directions.

 

[GSTdude06]

I have a the bottom hose hook into my BOV line and the other line going straight to the wastegate, I un hooked the other hoses and capped them on, one on the turbo and one on the intake. It was off ebay, said it was 0-30psi. And no I installed both then drove it. But my BOV doesnt make the PSH noise like it did before it was like PSHHHHHH now it just goes psh for like half a second then stops and I no I have a boost leak at my egr valve.

 

[eclipsh]

You don't want it hooked to the BOV. You need to reconnect the BOV to the intake or wherever you had it hooked up. Leave the one half hooked to the wastegate on the turbo and the other line going to the nipple on the turbo body/elbow.

EDIT: My bad, that's on a 1G. This is how to do it on a 2G.

 

[GSTdude06]

it said to connect it bottom line go to the BOV line so I used a T fitting and tied it into the line

like so...

You must be logged in to view this image or video.

 

[eclipsh]

I'd try doing it the way I have mine set up (as described above) and see what happens. It works great for me.

Oh, and were the lines you got cheap silicone ones? I've had those blow holes in them really quickly. I use thick rubber tubing or fuel line.

 

[GSTdude06]

I have mine exaclty how that picture is set up, im not sure what is going on tho...would a boost leak cause that problem? A messed up BOV?

 

[FastGS-T]

you may have a boost leak. spray soapy water across all of your pipes and TB and try pressurizing the system.

you might have gotten a bad mbc, or you may be over boosting, take out the screw and make sure the spring is still in the mbc...

 

[GSTdude06]

I no I have a boost leak at my EGR Valve and I no my BOV isnt working right.... would those cause this problem?

 

[oldman]

1. Is this a ball/spring or bleeder mbc?

2.

I have a the bottom hose hook into my BOV line and the other line going straight to the wastegate,

What exactly does bottom mean? Opposite but inline with the adjustment knob or the T nipple?

3.

would a boost leak cause that problem?

Affirmative.

4.

You don't want it hooked to the BOV. You need to reconnect the BOV to the intake or wherever you had it hooked up. Leave the one half hooked to the wastegate on the turbo and the other line going to the nipple on the turbo body/elbow.

I completely agree with this 100%, instructions are written by people so it can be wrong. If you want to get to the source of the problem, answer question 1 & 2 above then follow the following steps.

5. Cap off the T on the BOV line, connect a hose from the J-pipe/compressor nipple to the nipple opposite but inline with the knob (assuming you have a ball/spring mbc) and the other nipple (with a tiny bleeder hole) to the wastegate actuator. If the pressure holds steady between 10-12 psi, the problem was your pressure source from the BOV line, an indication that you have either intake or BOV leaks. If problem persists, go to 6.

6. Bypass the mbc all together by connecting a hose from compressor/J-pipe directly to the wastegate actuator. If pressure holds at 10-12psi, your ebay mbc is the problem. Possibly due to size differences between the ball and housing, spring too long/stiff or it's lacking the bleeder hole on the actuator nipple causing pressure to be trapped between the mbc and actuator. If problem persists, go to 7.

7. Perform a boost leak test and fix all leaks, you should be able to pressurize the intake tract up to 20psi and allow no less than 30 seconds before it bleeds down to zero, obviously the longer the better. If problem persists, go to 8.

8. Apply compressed air directly to the actuator, increase the pressure one psi at a time. If the actuator doesn't open fully before 12psi, you have a defective actuator that either doesn't open, opens too late or not fully. If it opens between 10-12psi, go to 9.

9. You most likely have boost creep, which should have been question #1. Does boost shoot straight up to 20psi or does it linger at 12psi a little then slowly CREEPS up as rpm increases?

 

[GSTdude06]

i connected the BOV line back how it was and connected the bottom line to tha compresser nipple like you said....the problem still exhistes, im thinking its my boost leak and my air/fuel ratio....I have a controller to change it what should it be set at?

 

[oldman]

i connected the BOV line back how it was and connected the bottom line to tha compresser nipple like you said....the problem still exhistes, im thinking its my boost leak and my air/fuel ratio....I have a controller to change it what should it be set at?

I spent a good 20 mins on my previous post last night, the least you can do is answer 1, 2 and 9 then try number 6.

 

[Spyderman7]

Do you have it adjusted backwards.

 

[GSTdude06]

Sorry oldman here is your answers....

1- yes I do
2- It is the line opposite of the adjustment knob going to the T fitting on the BOV line.
9- If I floor it it jumps to around 20-25psi, if I slowly press the pedal down it will creep up to 20-25psi and when I floor it is like studders in wont gain speed well.


I took away the line going to the BOV line and connected it straight to the compresser nipple like your thing said and its still jumping high. The knob is turned counterclockwise as far as I can get it without it falling off.


Im thinking its the leaks and air/fuel mixture is wrong but I could be wrong.



Oldman im falling what you gave me im fixing my EGR leak today (hopfuly) it will be fixed. Then I can find out where the other ones are cause that one is the loudest of them all.




-Logan

 

[oldman]

I took away the line going to the BOV line and connected it straight to the compresser nipple like your thing said and its still jumping high. The knob is turned counterclockwise as far as I can get it without it falling off.

Let's focus on this because it's important. Did you perform #6?

6. Bypass the mbc all together by connecting a hose from compressor/J-pipe directly to the wastegate actuator. If pressure holds at 10-12psi, your ebay mbc is the problem. Possibly due to size differences between the ball and housing, spring too long/stiff or it's lacking the bleeder hole on the actuator nipple causing pressure to be trapped between the mbc and actuator. If problem persists, go to 7.

or #5?

5. Cap off the T on the BOV line, connect a hose from the J-pipe/compressor nipple to the nipple opposite but inline with the knob (assuming you have a ball/spring mbc) and the other nipple (with a tiny bleeder hole) to the wastegate actuator. If the pressure holds steady between 10-12 psi, the problem was your pressure source from the BOV line, an indication that you have either intake or BOV leaks. If problem persists, go to 6.

Sounds like you're describing #5 not #6. Boost leaks aside, you probably have tons of them, it's clear that you're experiencing run away boost, this can only be caused by the following 3 things.

1. Reversing of the hoses in and out of the mbc. We have already eliminated this possibility.

2. A defective wastegate that never opens.

3. A defective or poorly designed mbc, most likely due to spring being too long or lodged side ways in the housing.

This is why it's important that you follow every step I listed in the oder they are listed. Performing #6 test will tell you whether you have a bad actuator or a bad mbc.

 

[eclipsh]

I took away the line going to the BOV line and connected it straight to the compresser nipple like your thing said and its still jumping high. The knob is turned counterclockwise as far as I can get it without it falling off.

Did you take the MBC out as well? FWIW, my Turbo XS MBC bleeds MORE air off when it is unscrewed and less when it is screwed in...

 

[GSTdude06]

Ok I got my gasket for my EGR valve and put it on so I DONT have that leak no more and the only other leak was my BOV which is bad so I put my BYPASS valve back on, everything is better BUT now it doesnt do it as bad but I still cant floor it all the way but now it doesnt go past 15psi before it went to 25psi. I havnt changed lines or anything my Bypass valve line is going straight to the intake now and I have the bottom hose on the mbc hooked to the compresser nipple and the other line going to the wastegate.

My wastegate fludders still so it would be working right?

Once it hits 15psi (very close to flooring it) it messes up but before it couldnt come close to flooring it.

I have to buy a new BOV cause the one I had was cheap and broke.

Could I being hitting fuel cut?


And I did perform 5 oldman sorry for the mis understanding

I will try 6 when I have some time and light outside

But right now its staying at 15 no more than that I just cant floor it competly right now.

 

[oldman]

Sounds like you're not done with the boost leak test, how much pressure was the intake able to hold and for how long on your last test after you block off the EGR?

 

[GSTdude06]

It was never blocked off I just was missing the gasket so all the air leaked out the sides.....

And I just hold the air pump on the nipple for a lil while then take it off and listen for leaking air.....

Im not sure if thats the correct way but it showed me 2 leaks...BOV and EGR both are fixed now

 

[oldman]

And I just hold the air pump on the nipple for a lil while then take it off and listen for leaking air.....

Im not sure if thats the correct way but it showed me 2 leaks...BOV and EGR both are fixed now

This is what you need to do.

1. Borrow an air compressor from Walmart.

2. Make yourself a leak tester.

3. Mix some dish detergent with water in a spray bottle, spray liberally around all gasket, coupler, TB, injector seals.....etc.

4. Disable or turn the mbc all the way up.

5. Pressure test and fix all leaks until the system is able to hold 20psi for about 30 second before it bleeds down to zero, go by the gauge in the car.

And you thought leak testing was a walk in the park.

 

[GSTdude06]

Ight I got the leak tester made and I have a air compresser and all that stuff....

So my problem is a boost leak for sure?!

Is my mbc bad cause it wont go to 1psi like it said it could or is that cause the leak to?

I want my psi around 11-12 for now until I get my 14B hooked up. And get a 255 fuel pump.

 

[eclipsh]

Yank the MBC and connect the wastegate directly to the turbo nipple. See what your max boost is. If it goes down to 10 psi it is your controller. Still check for leaks though.

 

[mr95gst]

If you are asking if the MBC will go to 1 psi it will not your wastegate is not that efficient to regulate the boost that low. You can only run the lowest number of boost that your actuator spring is set for the MBC can only turn up the boost from that point. It just regulates the air into the actuator to hold it closed to run more boost. Hope that answers your question.

 

[GSTdude06]

What if it stays around 15???

Leaks?

Or another problem?!