MBC Not working properly.

[evil_tsi]

I installed your average run-of-the-mill MBC the other day, and seem to be having some problems with it. I can adjust the screw either way, and it will decrease boost a little bit when turned out, but when turned in the car won't seem to boost past 13 pounds. I tried installing the MBC both ways just to double check and make sure I'm not a complete retard, but it still fails to adjust boost at all.

Any ideas, here?

 

[LordZed]

What brand is it?

How do you have it hooked up?

Does it run ok at 13psi or is there bucking and sputtering?

Did you order one with a ceramic ball?

 

[evil_tsi]

Problem solved. We took it out and the spring was caught in one of the threads inside the MBC. Cleaned everything out and we're running a good 17 pounds now.

 

[Fastgoat64]

What causes the bucking and sputtering? I just installed a mbc and thats what my car does now. Someone said boost leak but the car ran great before. Also it doesn't do it all the time but most of the time. Also the mbc doesn't seem to work right at all but after reading many threads on this maybe I should take it apart and look at the spring? I dunno I'm about ready to just take the damn thing off.

 

[romeen]

What causes the bucking and sputtering? I just installed a mbc and thats what my car does now. Someone said boost leak but the car ran great before. Also it doesn't do it all the time but most of the time. Also the mbc doesn't seem to work right at all but after reading many threads on this maybe I should take it apart and look at the spring? I dunno I'm about ready to just take the damn thing off.

These issues can be very frustrating but if you approach it rationally it will be easier to figure out. If your car was running great before the mbc install then there are a few things to consider.

1) Most boost leaks start leaking air only after a certain pressure is reached. If you have turned up the boost the increased pressure in the intake tract might have found a weakness (coupler, etc) that would have otherwise held tight under the lower boost that you were running previously. The fact that your car does this intermittently is also consistent with a boost leak that leaks only after a certain pressure is reached.

2) It could also be a leak along the routing of the mbc. Either in the vacuum lines or the controller itself. Is it a bleed off type or ball and spring type/restrictive controller?

3) It could be misfire. Again if your car only does it when accelerating hard or in higher gears this may be the cause or at least contributing to the problem. Check your plugs and make sure they are gapped at .028". The spark has a harder time bridging the gap when cylinder pressure is higher. Too large of a gap under high boost/load may not allow the spark to fire properly.

4) You could just be turning the boost up too high and getting timing pulled or even hitting fuel cut. You need to fill out your profile so we know what fuel system you're running, etc. Are you using an aftermarket boost guage?

I would start with the boost leak test and go from there. Hope this helps.

 

[LordZed]

These issues can be very frustrating but if you approach it rationally it will be easier to figure out. If your car was running great before the mbc install then there are a few things to consider.

1) Most boost leaks start leaking air only after a certain pressure is reached. If you have turned up the boost the increased pressure in the intake tract might have found a weakness (coupler, etc) that would have otherwise held tight under the lower boost that you were running previously. The fact that your car does this intermittently is also consistent with a boost leak that leaks only after a certain pressure is reached.

2) It could also be a leak along the routing of the mbc. Either in the vacuum lines or the controller itself. Is it a bleed off type or ball and spring type/restrictive controller?

3) It could be misfire. Again if your car only does it when accelerating hard or in higher gears this may be the cause or at least contributing to the problem. Check your plugs and make sure they are gapped at .028". The spark has a harder time bridging the gap when cylinder pressure is higher. Too large of a gap under high boost/load may not allow the spark to fire properly.

4) You could just be turning the boost up too high and getting timing pulled or even hitting fuel cut. You need to fill out your profile so we know what fuel system you're running, etc. Are you using an aftermarket boost guage?

I would start with the boost leak test and go from there. Hope this helps.

Super mega excellent post!

 

[Fastgoat64]

Its a ball and spring type, I guess I need to do i boost leak test. The only thing is it never gets passed 13psi, it cuts out just randomly to be honest. Actually I want to get a FMIC vary soon, would it hurt to drive it like this for a week if im easy on it?

 

[Fastgoat64]

I also just changed the plugs, (NGK) and gapped them to .30 it helped but only for about 50 miles.

 

[romeen]

Its a ball and spring type, I guess I need to do i boost leak test. The only thing is it never gets passed 13psi, it cuts out just randomly to be honest. Actually I want to get a FMIC vary soon, would it hurt to drive it like this for a week if im easy on it?

Since it's not completely clear what is causing the problems no one can say for certain whether it is safe to drive it. More than likely it is a boost leak(s) which doesn't really damage the motor. Running rich as a result of a boost leak will cause poor gas mileage, foul up spark plugs, and can allow some unburned fuel into the oil via blow-by. But nothing that will damage a motor in a short period.

I really feel that boost leak tests should be a part of routine maintenance. Make yourself a tester as shown in the tech section and get comfortable with using it. Trust me, it will prove invaluable in keeping your car running well.

Since putting in new plugs seemed to help for awhile I would try pulling them and gapping them to .028". If they are black and smell like fuel then that could be yet one more indication of a boost leak.

Fix your boost leaks. Then if your car is still not running well let us know.

 

[turbosax2]

The correct gapping is .028

 

[Fastgoat64]

alright I will pull them and have a look, thanks for the advice and I will let you know how they look.

 

[Fastgoat64]

Okay i pulled my plugs and they look like its running right, maybe a little lean actually. The weird part is when I first installed them I gapped them at .30, when I went to check them they were all at .25.....Wierd? I also changed my boost source to the compressor housing and I get boost much quicker it seems, but the car is still running like crap. I also went to menards last night to try and get everything to build a boost leak tester and I found everything but a shrader fitting. They had nothing that i could see that would make it possible to pressurize the system, so i'm going to the hardware store to have a look and if no luck there i'llgo to home depot. I never even noticed the tech section on this site, it's incredible to say the least, tons of information and diy techniques.

 

[Fastgoat64]

Okay, built myself a boost leak tester, works great. My intercooler has two holes in the neck the comes up through the fender well So I kind of rigged it to get me by til I can get a front mount kit and checked it and no leaks. So I put it back together and go for a test drive and still runs like crap when under boost. My exhaust sounds like a machine gun it sputters so bad. I pulled my intake back off and put my tester back on and I have a leak coming from the turbo somewhere? Cant find it but thats where it is definately coming from. Maybe its time to get a 16g?

 

[romeen]

Okay, built myself a boost leak tester, works great. My intercooler has two holes in the neck the comes up through the fender well So I kind of rigged it to get me by til I can get a front mount kit and checked it and no leaks. So I put it back together and go for a test drive and still runs like crap when under boost. My exhaust sounds like a machine gun it sputters so bad. I pulled my intake back off and put my tester back on and I have a leak coming from the turbo somewhere? Cant find it but thats where it is definately coming from. Maybe its time to get a 16g?

Did you use the soapy water out of a spray bottle technique to help identfiy the leaks? If not it is easy to miss some. This technique should help you to locate even the smallest leak.

How did you determine that the turbo itself is leaking pressurized air?

Specifically which NGK's are you using?

 

[staticbrainwash]

People also run into sputtering and bucking sometimes when they tap an mbc into the BOV line.

Make sure you run it from the compressor or outlet elbow on the compressor, and leave your Bov line for just that. . . the bov.

 

[kenamond]

You should be able to pressurize to 20psi and have it leak down no faster than 1psi every few seconds on a warm motor. Ring blowby on a cold motor will seem like a big boost leak, so make sure the motor is warm.

Also, all ball/spring and bleeder MBCs have a bleeder hole that will act like a boost leak. Make sure you cap or kink the MBC input line.

Pull the oil cap before the test so that you don't accidentally pressurize your crank case.

Listen to romeen.

 

[fisherob]

most problems seem to be boost leaks... should you use your boost pressure when testing?

 

[kenamond]

most problems seem to be boost leaks... should you use your boost pressure when testing?

I go 5psi higher than my boost level. You'll have boost spikes that are higher than your normal boost level. If it can hold 5psi more, that's just proving the system is not leaking ever.

 

[viprez586]

My exhaust sounds like a machine gun it sputters so bad. I pulled my intake back off and put my tester back on and I have a leak coming from the turbo somewhere? Cant find it but thats where it is definately coming from. Maybe its time to get a 16g?

Check the O-ring around the Compressor ring that seals with the housing
You'll also notice when you put the C-clip back in it is harder to seat, in my case i took a brass hammer and a flat head to gently tap into its groove providing a tight seal. Some people put high temp RTV around this clip but its your choice. A good place to put some high temp RTV though is the compressor elbow

Credit for pics goto VFAQ.com

 

[staticbrainwash]

Can you get just that o-ring? Because otherwise my 14b is all set, but i've got an interior leak it sounds like and that seems like the most likely culprit.

 

[viprez586]

Yup goto MACHV.com its under compressor o-ring. i think in the maintenance section

 

[staticbrainwash]

How hard is it to replace this thing? Looks as though a whole turbo removal is necessary. Or can i just pull the compressor housing off without removing all the lines?

 

[viprez586]

If your snap ring is in an easy enough position, props to you if you can get it off.
I had to remove my whole turbo. But hey you can use some simple green to make that compressor cover look brand new while you got it off!

 

[MelloEclipse]

how about my MBC seems completely stuck, and i'm not really sure what to do about it..... i'm not sure if it's seized or what, but the screw has NO freeplay in either direction...weird huh?

 

[viprez586]

What kind of boost controller is it?
I have a Hallman EVO In-Cabin. Mine was not providing any adjustment, all i did was dissasemble the BC at the boost source in nipple to find a ball and spring. Remove these, clean them + lightly dab some grease on the ball+spring. Reassemble and your smooth sailing.