New MBC, Weird Issues

[Madcow1041]

I bought a new MBC from Dejon and installed it today. Knowing that I would have to make some adjusting, I kept the adjustment screw where it was, and since I didn't install it at my own home, kept boosting to a minimum.

I read around and found out that loosening the screw lowers the boost pressure, so I did that as far as I could without it falling out. I go out to test the boost, and as soon it starts to reach what I would consider around 60% stock boost (which I was assuming that it was at, although I do have an aftermarket boost gauge), I hear this really loud screeching noise. Not that of a belt, mind you. Just a really loud, high pitched screeching. It sounded like someone taking their nails to a chalkboard but amplified five fold. I was watching the boost gauge the whole time and it said it went 20+ or something like that. I also tried screwing the adjuster in all the way, and same thing. I immediately refrained from boosting at all until I could make it home, and that's where I am now.

I thought the noise could be knock, but reading around it sounds like it's not, so I'm very confused... Especially never having heard knock in the first place.

So, I guess my questions would be:

1) What could that noise possibly be?

2) Why doesn't my boost pressure go down with any adjustment?

Any and all help would be appreciated!

 

[Boost95]

You wont hear knock. The engine will hear it way before you can. 1st thing to do it check you vacuum lines for your MBC. Look the see if the line is kinked anywhere. That may cause the wastegate not to see a signal and overboost. If that checks out okay, do a boost leak test and post up.

 

[dustn03]

+1 check the vacume line and also you may have got a bad mbc

 

[S_Ranger]

I've had that noise because my mbc setting was too high and I had a leak. That's why it is important to have an a/m boost gauge installed before the MBC is in test. Since you have one laying around just hook it up real quick and post up. Turn the screw all the way out too so you can start from the bottom, 12psi, and work your way up.

 

[Madcow1041]

Thanks a lot for the replies. I'll have to run those tests out later, seeing as though it's 3:30 in the morning and really freaking cold outside. After I'm done, I'll post the results. But for now, I need some sleep because I've got a long day ahead of me.

 

[Madcow1041]

Well, I'm still in the process of working on the car.

I just did a boost leak test. The bottom of my BOV was leaking, so I fixed that. But, there's another leak on my BOV (coming from the set screw on top) that I don't know how to get rid of. I bought the car with a Greddy Type-S already in it. Is there supposed to be some sort of O-ring or gasket-type object on it?

Other than that, there are no more leaks. The MBC checks out (I think... I'm not extremely sure about how to tell whether it's working or not... ). I'm just waiting for my friend to bring by my boost gauge so I can see how many pounds I'm putting out, and fix it.

 

[MyBeatGSX]

The noise sounds like either the compressor blades hitting the housing or a lot of air being forced through an extremely small boost leak hole.

Does the turbo have any shaft play? That would be number 1 to check.


Make sure you connected all the vacuum lines to the correct sides of the MBC. You could be blowing boost out the vent/bleed hole, which would probably make that sound you heard and also give you no boost control.

Yes, the type s should have a gasket on the bottom. They are also notoriously leaky. Teflon tape the threads on the nipples and the adjuster screw.

 

[Madcow1041]

More testing will have to wait for another day. I just got the boost gauge an hour ago and it's dark out already. I need to use teflon tape all of the threads yet, but based on what MyBeatGSX said, I believe the noise is coming from the hole where the adjustment screw on my BOV is. I haven't checked the play in the compressor yet.

 

[Madcow1041]

Okay, so I've pretty much narrowed my possibilities down to two:

1) BOV leak causing un-regulated boost?
2) Bad MBC

I finally attatched my boost gauge. My gauge measures up to 20 psi. The boost jumps past 20 at WOT, which is why I reach fuel cut (obviously speaking). I'm going to use one of my friends BOVs and/or MBCs and see which brings me closer to, if not completely, fixing my overboost problem.

I still haven't checked out my compressor wheel, but I'm pretty convinced that the noise is coming from the adjustment screw on my BOV.

 

[Madcow1041]

Mm... Problem solved. I was prompted to switch around the hoses on my MBC...

Turns out they were connected the wrong way on the MBC. It also turns out that they were marked incorrectly in the first place, so yeah. Thank you for all of your help!