New MBC not working..

[the_red_pooch]

Ok, I bought a cheap MBC off ebay just to make due for a few weeks when I could offord to buy something better because I haven't decided if I want to buy a standard mbc or a dual stage yet. And I had a bad snowmobile accident this weekend and broke my collar bone(compound fracture) and won't be working for awhile so I'm poor atm. Anyways, I bought I believe it was a voodoo mbc and I'm almost positive its installed correctly. The only thing I didn't do was block off the stock bcs nipples, they're open and just hanging there. Now I installed this and it had almost no effect at all no matter how far I turned it in either direction. The only difference I have noticed is I only run 12 psi instead of 13 and it falls to 10 by about 6000 rpms! I have no idea whats going on. I'm sure I get what I pay for but honestly they can't sell something that doesn't even work at all whatsoever can they? Maybe i did something wrong, I'm just askin for opinions or possible answers as to why its doin this.
Thanks,
Dustin

 

[romeen]

Sorry to hear about your collarbone.

Don't worry about the nipples on your stock BCS. You can cap them if you want to keep dirt out of there but it won't affect boost control in any way now that you are bypassing it. Just keep the electrical harness attached to it to avoid a CEL.

You stated that you're "almost positive" that you hooked up the pressure lines correctly. I would recheck it so that you are 100% sure. Also if you describe to us exactly how you have it hooked up we might be able to help you better.

 

[Spooling99]

Where did you route your boost source and vaccum sorce to? Hopefully you didn't "T" into the bov line.

 

[the_red_pooch]

Uh oh, I did T it into the bov line. As for how I installed it, I installed it identical to a diagram I found on the forums here. And I read the how-to on installing them on these forums too. I'm not exactly sure if it was a how-to, but it was a pretty indepth description atleast. My BOV line has a T in it for my boost gauge and one for my MBC. I believe the other end of the BOV line goes into the intake over towards the cam gears. But back to the MBC, from the T in the bov line it goes to the mbc and then down into my wastegate on the turbo. I just reused all of the stock lines that went to the bcs. Where should I move the source line to?

 

[kenamond]

Uh oh, I did T it into the bov line. As for how I installed it, I installed it identical to a diagram I found on the forums here. And I read the how-to on installing them on these forums too. I'm not exactly sure if it was a how-to, but it was a pretty indepth description atleast. My BOV line has a T in it for my boost gauge and one for my MBC. I believe the other end of the BOV line goes into the intake over towards the cam gears. But back to the MBC, from the T in the bov line it goes to the mbc and then down into my wastegate on the turbo. I just reused all of the stock lines that went to the bcs. Where should I move the source line to?

Instead of going from the T on the BOV line, go straight from the compressor outlet nipple where the old BCS connected (don't leave the now-exposed "T" nipple open).

The lowest boost you can run is the stock WGA actuation pressure which is around 10-12psi. If the MBC is hooked up correctly, you may not be tightening it enough.

also, there is a 3rd vaccuum line for the stock BCS that connects to the intake pipe (pipe between the air filter and turbo compressor inlet). You need to cap the nipple on the intake pipe or you have a vaccuum leak. That won't affect your boost situation, but should be done nevertheless.

EDIT: It's not a huge deal to T into the BOV line, but it's discouraged. Not like you're going to blow your motor over it in a day.

 

[the_red_pooch]

Isn't the compressor outet nipple the little nipple off my wastegate? I have it connected from that nipple to the mbc and then from the mbc to the T in the bov line. I'm not exactly sure what you're saying I guess as to where else to route the mbc line instead of the bov line...

 

[romeen]

Dustin, got your PM. Go ahead and route it like Mack says. Make sure the lines to the MBC are hooked up correctly as far as the line "in" and "out". Let us know how it works after you reroute the lines.

As far as boost falling off a little around 6000 rpm it's probably just the turbo running out of steam. Furthermore the 14b exhaust housings are prone to developing cracks, especially around the seat for the wastegate flapper. This can also have a slight effect on boost response and boost levels.

 

[romeen]

Isn't the compressor outet nipple the little nipple off my wastegate? I have it connected from that nipple to the mbc and then from the mbc to the T in the bov line. I'm not exactly sure what you're saying I guess as to where else to route the mbc line instead of the bov line...

Doh!! No wonder it's not working. The boost/pressure source is going to be the nipple on the j-pipe (14b's dont have a nipple on the compressor). If the j-pipe doesn't have a nipple then you will need to put one on (easy to do). This line will send the pressure signal to the mbc. The line "out" from the mbc goes to the nipple on the WGA. What pressure source was being used previously? For the time being go ahead and reverse the lines. Line from BOV hose to "in" port on mbc and line from "out" port to nipple on WGA.

 

[kenamond]

Isn't the compressor outet nipple the little nipple off my wastegate? I have it connected from that nipple to the mbc and then from the mbc to the T in the bov line. I'm not exactly sure what you're saying I guess as to where else to route the mbc line instead of the bov line...

There's a nipple on the compressor outlet (where the compressor scroll opens up and heads to the intercooler) and one on the goldish "can" (WGA) bolted to the compressor housing. The compressor provides signal to the WGA telling it to open at ~11psi. This ends up bypassing exhaust gas around the turbine wheel so that boost doesn't continue to rise. The BCS or MBC intercepts that signal, makes it look lower, then passes it on to the WGA. The MBC lets you manually change how much boost you hide from the WGA, thus giving you control over your boost level. The more of the signal you hide, the higher the boost level you'll end up with.

 

[JayRolla]

Still even if he does switch the mbc it does not explain why it was not working. The line at the bov will still allow him to control boost.

 

[the_red_pooch]

Well I tried to switch the "in" and "out" lines and it just made it go back down to about 10 pounds and falling. It only falls when I have this stupid MBC hooked up backwards or when I have the dial opened way up. The only way I can get close to stock performance back is if I have the adjustment knob screwed all the way in flush. Then its back to about 12-13 psi, otherwise I only get 10 psi if I adjust the mbc knob out (I'm assuming its just working off of the wastegate spring when this happens). The only nipple I can find anywhere on my turbo is the one coming from the wga(its not a goldish can exactly because its surface rusted pretty good but I assume its what you are talking about. Its roundish in shape and 2-3 inches thick bolted on the compressor). I'm running my "in" line on the mbc from this and the "out" line on the mbc is going to the "T" in the bov line. So I don't know what I'm doing wrong. It looks identical to the diagram I have. Thanks for the patience guys, sorry I don't know more about what I'm doing... .

 

[kenamond]

Well I tried to switch the "in" and "out" lines and it just made it go back down to about 10 pounds and falling. It only falls when I have this stupid MBC hooked up backwards or when I have the dial opened way up. The only way I can get close to stock performance back is if I have the adjustment knob screwed all the way in flush. Then its back to about 12-13 psi, otherwise I only get 10 psi if I adjust the mbc knob out (I'm assuming its just working off of the wastegate spring when this happens). The only nipple I can find anywhere on my turbo is the one coming from the wga(its not a goldish can exactly because its surface rusted pretty good but I assume its what you are talking about. Its roundish in shape and 2-3 inches thick bolted on the compressor). I'm running my "in" line on the mbc from this and the "out" line on the mbc is going to the "T" in the bov line. So I don't know what I'm doing wrong. It looks identical to the diagram I have. Thanks for the patience guys, sorry I don't know more about what I'm doing... .

It may be that the MBC spring (if it's a ball-spring type) is not stiff enough. If you can disassemble the MBC and take the spring to the hardware store, you should be able to find a spring of equal length and diameter but with greater stiffness (not too too much). Some MBCs are designed to up the boost a few psi max.

 

[romeen]

Dustin, I just want to make sure I am understanding you.

1) You ran the vacuum line that is teed into the BOV line to the "in" port on the mbc.
2) You ran a hose from the "out" port of the mbc to the nipple on the wastegate actuator (the can that is bolted to the turbo).
3) You then tried to turn up the boost by screwing the adjustment knob clockwise (tightening it) and when it was screwed in as far as it would go the boost only went up to 12-13 psi.

If that is the case then the mbc is probably defective. If you have a boost leak tester you can check it. Hook up the mbc as I've stated except leave the end that attaches to the WGA unhooked. Have a friend plug up the end. Pressurize the intake like you normally would for a BLT. Then check how rapidly the pressure is being released past the mbc. The rate of release should get less as you screw in the adjustment knob. If you don't have the means to do a boost leak test then I suppose you could get some idea by blowing through the "in" hose. As you tighten the adjustment knob it should become harder to blow through it with less air coming out the other side.

 

[the_red_pooch]

Romeen, yes thats correct. When I got it I tried the blowing through it with my mouth thing and as I tightened it yes it did get more difficult to blow through until I couldn't at all. I think it may be defective though, I suppose I'll end up just waiting and maybe purchasing a better quality mbc. I don't know what else to do . Maybe I can find a good used one on the classifieds or something. Any suggestions for something cheaper but will actually work? . Thanks again guys.
Dustin

 

[Fastgoat64]

Man we must have the exact same MBC because mine is doing the exact same thing except if i hook it up backwards it makes more boost but the car cuts out and pops right at 13 psi.

 

[kenamond]

Romeen, yes thats correct. When I got it I tried the blowing through it with my mouth thing and as I tightened it yes it did get more difficult to blow through until I couldn't at all. I think it may be defective though, I suppose I'll end up just waiting and maybe purchasing a better quality mbc. I don't know what else to do . Maybe I can find a good used one on the classifieds or something. Any suggestions for something cheaper but will actually work? . Thanks again guys.
Dustin

You can get a "good enough" MBC for under $50 new. The cheaper you go, the more chance of getting another defective one. Did you try disassembling the MBC to take out the spring? A stiffer spring will cost you under a buck. A new MBC is a lot more than a buck.

fastgoat64: Hooking up the MBC backward is a bad idea. It is about the same as snipping the hoses and tossing it in the trash. The WGA gets no boost signal, so there's nothing to open the wastegate, so you overboost. The other end leaks boost and is a boost leak (the MBC has a bleeder hole on the "out" side, so hooking it up backward is a boost leak). You may be hitting fuel cut due to this and potentially other boost leaks. The ECU will cut fuel and spark when it senses too much airflow, and it is a safety net for a non-functioning wastegate actuator. You shouldn't hit fuel cut at 13psi unless you have significant boost leaks. The turbo is sucking air through the MAS which meters air flow. If most of that air is leaking between the turbo and the combustion chamber and the turbo is overboosting, the air the ECU sees can be much higher than what's making it into the combustion chambers.

 

[Fastgoat64]

Well it didn't make any sense to me to hook it up backwards, but I read many posts on the MBC and quite a few people were encouraging it if it wasn't working the right way. Figured I'd give it a shot, bad idea, now the car hesitates really bad til about 1500 rpms.