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.

 

[eclipsh]

One step at a time. Go try taking the MBC out of the picture. It'll take five minutes to do and test. Do it now and get back to us

If you didn't have problems like this before installing the MBC then it is likely either how you installed it or it is the MBC.

 

[GSTdude06]

Ok I disconnected the MBC competely and hooked the hose straight to the wastegate

It still goes to 15psi but then around 5 6000rpms it goes down to around 10 11psi.....

When its at 15 it studders but still goes....

 

[oldman]

That means your mbc is OK and the actuator is old and slow to react. The bogging and boost dropping off is probably partly due to more boost leaks and the typical T25 dropping off at upper RPMs.

 

[GSTdude06]

ok so can I hook the MBC back up?

Where would be a leak come from?

Should I just soap down the gaskets and hoses and test it?

And thanks for all the help people and thanks ALOT oldman

 

[oldman]

ok so can I hook the MBC back up? Yes.

Where would be a leak come from? Don't know.

Should I just soap down the gaskets and hoses and test it? Yes.

thanks ALOT oldman

You're welcome.

 

[GSTdude06]

anytime....

your the most help anyones gave me on this site!!

but others gave me help to! so noone get mad

 

[GSTdude06]

Ok so I soaped the engine found some bubbles coming from a screw on the throttalbody why there I have no idea.....

Cleaned everything off and tightened that screw (was very loose)

Drove it around worked perfectly!

NOW.......

Its doing it again....

it was stayin around 10 11psi but now once again 15..

Car studders and what not...


Another leak somewhere else?!

And is all this normal for a eclipse cause I would like it to boost fine

 

[oldman]

Ok so I soaped the engine found some bubbles coming from a screw on the throttalbody why there I have no idea.....

BISS screw, did you just spray soapy water and let the car idle or did you pressurize the intake.

Cleaned everything off and tightened that screw (was very loose)

You can't just turn the BISS screw when ever you want, read this following link so you understand what it's for. http://www.vfaq.com/mods/BISS-2G.html

Bottom line, are you sure you follow #7 exactly as written and all conditions were satisfied?

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.

 

[GSTdude06]

i soapy watered the engine and everything yall said to do and pressurized the intake...

that screw i mmoved so i idle at 750 now

havnt drove it yet im bout to in a lil bit... ill post how it goes

 

[oldman]

i soapy watered the engine and everything yall said to do and pressurized the intake...

Dude, no offense, pressurize the intake using an air compressor, not by turning on the car. Obviously, you didn't click or read the boost leak test or BISS screw link I posted. I can only give you directions, you have to read/learn and then perform the tasks on your own.

 

[GSTdude06]

dude I did presserize it with a air compressor..........

i said i did....

and i read everything u post and follow EXACTLY what you say to do

 

[oldman]

Are you saying your boost gauge said you pumped 20 psi into the intake and held it for 30 seconds and all you found was a leak at the BISS?

If you have read and study the BISS page I linked you to, you would have known that the reason it was leaking is because the BISS oring is worn and needs to be changed. More importantly, you would have known that you can't just go and turn the BISS screw when ever you want, there are specific procedure which must be followed when adjusting the BISS.

 

[GSTdude06]

well I turned the screw b4 you gave me that page so it was already turned I just made it go to where I idle at 750.......

I guess I should get a new o ring for it that was the only place I could see bubbles coming from tho....

 

[oldman]

Are you saying your boost gauge said you pumped 20 psi into the intake and held it for 30 seconds and all you found was a leak at the BISS?

Did it really hold 20psi for 30 seconds before it bleeds down to zero? This is important.

 

[GSTdude06]

idk I didnt check that tomorrow ill look at that.....

I should hold 20psi on the boost gauge for 30 seconds?

 

[oldman]

I should hold 20psi on the boost gauge for 30 seconds?

It will likely start to bleed down immediately after you stop pumping, look for 30 seconds before it gets to zero. My guess is that you're a long way from 20psi right now.

 

[bigdogg2834]

I have one of those ebay MBC's and was having the same problem as you. I thought that the spring might be too long because like you I could only loosen it so far before the screw would come out, and I was boosting like 20 psi. So I took the spring out and clipped off about half a coil and now it works fine I can turn it down to 12 if I want to. So that could be the problem with yours.

 

[GSTdude06]

ill clip the spring if I HAVE to but ill go buy another spring before I do that incase it mess up.....

 

[oldman]

ill clip the spring if I HAVE to but ill go buy another spring before I do that incase it mess up.....

We have already determined it's the actuator, not the mbc since you were still boosting 15psi with the mbc removed from the system.

 

[GSTdude06]

ok good....

so its my wastegate? do I need a new one?!

 

[oldman]

ok good....

so its my wastegate? do I need a new one?!

You have two different issues here.

1. You are boosting 15psi instead of 10-12psi with the compressor/J-pipe connected directly to the actuator Probaby due to the actuator opening too late unless the hose you used is leaking. I do not see a problem with you boosting 15psi so I don't see the need to replace it.

2. The car is bogging during WOT, that's why you're leak testing. I think you're getting the two problems mixed up.

 

[GSTdude06]

ya een taking th mbc out its still 15 so that owuld mean its a leak....

that what your saying?

right now im installing my 3" exhaust so when im done with that I can leak test it some more

thanks for the help

 

[eclipsh]

No, what he is saying is that you have two things wrong with your car that are not related.

You are boosting 15 psi because the little brass can, called the wastegate actuator, is broken. This has nothing to do with intake leaks. It is a bad part that you should eventually replace.

The rough operating at full boost is because of the leaks in your intake. It is a completely seperate issue. It is also important and needs to be taken care of first. THAT is what you are pressurizing the intake for.

 

[green_bread]

Yes... follow the oldman.. he is wise....


The wastegate acutator should really be the least of your concerns, RIGHT NOW... Like it was said before, all it does is open the wastegate at a certain PSI so that the turbo wont build any more boost.

FIX THE BOOST LEAKS... trust me, you will be HAPPY you did and devote your time to fixing the before you start adding other things on to the car(which has been preached here time and time again). Not trying to be a prick, but why would you put on a 3" exhaust before you got this problem figured out?

GSTdude06:Ignore this part and go fix your boost leaks....
-------
I did have a question, though... he said that with no MBC peak boost was at 15 PSI before dropping to around 10-11. When the MBC was installed, he said he was spiking up to ~25 PSI. Is this something that could be caused by the spring being too long/too stiff?
-------


ADAM

 

[oldman]

I did have a question, though... he said that with no MBC peak boost was at 15 PSI before dropping to around 10-11. When the MBC was installed, he said he was spiking up to ~25 PSI. Is this something that could be caused by the spring being too long/too stiff?

I suspect that he had the mbc hooked up backwards in the beginning, reason why he was boosting 25+ psi.