MBC issues or is it me...?

[bryan_tberry]

Alright, I installed my Dejontool MBC this afternoon and per directions backed the screw out to a point in which I could barely blow air through, and set the lock nut. (I also made sure and installed the MBC correct, as I've been reading of DSMers hooking up the wrong hoses to the wrong nipples.) Anyways, I double checked everything and took off and boost was terrible. It would hit the normal 12-13 PSi it had done before, but was VERY stuttery and weak. I turned the screw inward about a half turn, and that seemed to help. For about 3 or 4 runs in an empty lot, I kept adjusting the screw in, and although it felt slightly different after the 3rd time, (pulled a little cleaner/harder), it still never boosted above 13lbs. Okay, no big deal, I'll just keep turning the screw. A whole six rotations later, I'm still pulling 13lbs.

Now, I suspect the culprit to be one of a few things and I plan on working with it as soon as I get out of work here. First, I'll keep turning it in and see if that makes a difference. It isn't all the way in yet. I have around an inch of thread left. Also, I have a boost leak in the throttle body shaft seals, which I'm pretty positive is the bad guy here... which makes me the bad guy for putting off the repair, . I'm going to try a few things as mentioned earlier, as well as hook up the pressure hose to the turbo instead of the line from the BOV to the IM. Wish me luck, and feel free to add any ideas/pointers.

 

[bryan_tberry]

Okay I turned the MBC all the way in and still no more boost than 13lbs. I'm nearly certain it's the boost leak. I didn't think it would be that dramatic of a change... is there anything I'm overlooking?

 

[oldman]

Okay I turned the MBC all the way in and still no more boost than 13lbs. I'm nearly certain it's the boost leak. I didn't think it would be that dramatic of a change... is there anything I'm overlooking?

Boost leaks will have to be fixed no matter what but it would have to be a huge leak for the turbo to not boost over 13psi. Remove the hose going to the actuator and go for a test run, this should result in infinite boost so feather the throttle and let off before 20psi, the objective here is to see if you're able to boost past 13psi. If in fact you're able to, the mbc is the problem. If problem persists, the problem is most likely a major exhaust leak (maybe cracked turbine housing), boost leaks (probably more than just shaft seals) or a dying tubo, maybe it's all of the above.

 

[Ultimatedsm]

You want the fix to your problem? Seems like your car is pretty much stock with the freemods only. You put on a MBC without changing the stock 2g BOV? The first thing you should change on the 2g cars is the BOV because it leaks past 13 psi, you will not get any more boost then 13-13.5 psi. Put on the 1G BOV (good for 18 PSI or more if crushed) or get some other BOV that can be recirculated (Greddy Type RS). Anyway, try the BOV first then come back to us. Hope that helps you out.

Another side note, if you continue to turn up the boost like that your T-25 will cook itself to death .

 

[TurkF26]

Couple questions.

First off are you running stock IC piping with stock BOV?? they tend to leak horribly if you try to run any more boost that stock.

Also how/where do you have your boost line ran too?? if you have it just stuck in a vacuum line zipted there, that could be your problem. Easiest thing to do in that case is to go to your local hardware store, but a brass union, a brass T coupler, a little ferrell thing that connects to the end of the boost line (If you already dont have this done) and hook that up to where your brake booster line goes into your intake manifold. Dont forget to hook your brake booster line back into the brass T.

Once you have checked both of these let us know. Im pretty sure the TB shaft leak is not gonna do that to your car. Seems like to me it has to do with how you are reading your boost.

 

[Ultimatedsm]

Couple questions.

First off are you running stock IC piping with stock BOV?? they tend to leak horribly if you try to run any more boost that stock.

Also how/where do you have your boost line ran too?? if you have it just stuck in a vacuum line zipted there, that could be your problem. Easiest thing to do in that case is to go to your local hardware store, but a brass union, a brass T coupler, a little ferrell thing that connects to the end of the boost line (If you already dont have this done) and hook that up to where your brake booster line goes into your intake manifold. Dont forget to hook your brake booster line back into the brass T.

Once you have checked both of these let us know. Im pretty sure the TB shaft leak is not gonna do that to your car. Seems like to me it has to do with how you are reading your boost.

Beat you to it sucka!! just kidding. By the way DO NOT "T" the MBC to the BOV line!

 

[TurkF26]

ya u did ultimate... it seems more like to be related to how he is getting his boost reading because even with the stock 2g BOV leaking, you would still see mor than 13lbs with the MBC backed all the way out. i really want to know how he has that gauge hooked up...

 

[oldman]

The brake booster line? I hope I'm reading it wrong. Routing should go from compressor to mbc then from mbc to actuator, short and simple, no need for T fittings.

 

[TurkF26]

No im not talking about the routing for the MBC from the Brake Booster line, I was refering to the correct way to hook up the boost gauge.

 

[oldman]

No im not talking about the routing for the MBC from the Brake Booster line, I was refering to the correct way to hook up the boost gauge.

The brake booster line isn't a good place for the boost gauge either, there is a check valve in the booster line that opens under vacuum to assist with braking which might affect the accuracy of the gauge reading. The boost gauge should be tapped to the fps/fpr line.

 

[TurkF26]

its a rought sketch but as long as the T is before the one way valve its fine. The T is attached right off the intake manifold and before the 1 way valve.

http://cowtownturboworks.com/forum/...b350b69b89043a00045d5028197cbb&sort=1&cat=505

 

[bryan_tberry]

As far as my boost guage goes, I installed it on the vacuum hose coming out of the IM on the drivers side; seems to be a typical spot to tap it. I even used brass fittings. I'll try to get some pics up. And yes, I'm still running my stock I/C piping. I beleive I mentioned I was stock other than free mods, a boost guage, and an MBC. I do have a new BOV and U/LICP coming to me in the mail, and my FIPK is waiting here on my couch to be installed in the next few days. Oh and oldman... you made my night. I was hoping those shaft seals wouldn't make too much of a difference. Tomorrow I'll bypass the MBC and post results. I'd really love to get this resolved. Thanks for your input so far, Ill let you all know.

 

[TurkF26]

the problem i have found using anything other than secure brass fittings off the intake manifold is that the boost reading is not accurate. all the plastic T's, etc... dont do well over 20lbs of boost and is not that accurate. i have had no problems what so ever with the setup i have directly off the intake manifold like i posted in the picture link.

 

[bryan_tberry]

Alright here's a pic of my boost guage tap/instalation. Seems like it should be okay in my eyes at least.

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[TurkF26]

u might have some leaks where those hoses go into the brass T. Try to maybe find some hose clamps to go over those so they are securly tight along those barbed fittings.

But now looking at how your line is setup, it may leak a little but you should still be able to read over 13lbs of boost. Id also recommend what oldman said and try to unhook everything and run unlimited (unsecure) boost and see if you can get it to go over 13lbs.

 

[bryan_tberry]

Yeah I'm pretty positive I'm not leaking out the boost guage tap... RTV works wonders. As soon as I'm out of class here, I'm heading to my apartment to mess with everything. Thanks, I'll let you all know.

 

[bryan_tberry]

Alright, I've got an update for my situation, hope somebody can shed some light. i'll jump straight to it. I disconnected my hose coming from my wastegate to my MBC and took it for a spin. Results: 13PSI tops. Wouldnt boost past that. So, that being said, I think at 13psi, my stock BOV is leaking. Anyways, I reconnected everything and it runs the same. I stlll have the boost leak in the throttle body. Also, I can literally feel the car trying to push forced air into the motor. It's like something is just pulling it back from its full potential. (My friends nearly stock 3G GT 5SPD walked away from me.) How much of a difference would auto make? When I'm cruising with overdrive off, at about 3kRPM, thast my sweet spot. I boost pretty well from there, but it still feels a tad weak. I'm hoping this is just boost leaks. I'll report back when I get my U/LICP in the mail.