Trouble Controlling Boost with MBC

[theKnifeArtist]

i've been running stock boost for about a year now after my headgasket job. Before that, when i got my ddp, i was using a manual boost controller that i was given from our friend empera. the problem i had then was when the mbc was installed, i had max boost, or boosting till fuel cut(14ish) with it adjusted to as much out as possible. this was back when it was automatic, mind you. i didn't know what the deal was, but i didn't bother with it after my HG job.

well today, my buddy was bitchin' to me about how my damn wastegate is always open and about my boost leak at around 12psi that i never fixed. Ever drive a supra with a ddp on stock boost? hehe, yeah it makes a lot of noise just driving around normally through the gears. so, i had nothing to do today, so i decided to do this shit.

Fixed the boost leak and installed the mbc. Same problem as before. I have the screw undone as far as i can, and bam 14psi with fuel cut through any gear. I can't drive it past part throttle.
Anyone have any idea of what it can be? i know i have it hooked up correctly. Can the mbc be faulty? i took it apart and looked over the whole thing and it seems fine. Any ideas or anything is appreciated.
Thanks.

 

[jtran8]

First , supra love ebc ; second , if you want mbc make sure to use the one that has ball and spring like ( Drjone mbc) . now if your car hit 10+psi without boost controller , that's mean you have boost creep ; but if your car ran fine before and now you have problem after install it , thats mean either you install it wrong or you have bad boost controller .There are two ways to find that out, one run without mbc and find out ; two while you take it out , use mouth blow through it and use your finger to turn knob in and out to see how it works . remember some mbc back out knob mean turn up the boost for example TURBOSMART mbc . While other mbc turn the knob in mean turn up the boost . thats why you need to test it by blowing through it ,and make sure the hose that hook between boost controller and wastegate actuator no more than 18 inches or shorter is beter .good luck !:icon_bigg

 

[theKnifeArtist]

-I am aware of my boost creep. The stock wastegate cannot handle stock boost levels with a 3" exhaust and the wastegate dump tube on the ddp. i'm not worried about that though, because i plan to run it at around 12, and it'll be good for that.
-i remember doing the blow test on the mbc and it gets harder to blow through when tightened. here is a picture of what it looks like on the inside, the drawn in stuff is the ball and spring.

i talked to a teacher about it and he said it could be a mbc for higher boost levels, thats why it won't go as low as i want it, but i dont think this mbc is meant to be controlling boost levels at least above 14psi

 

[tlo86]

just do what i did. go to a fish store and buy fishtank fittings and make your own MBC will cost 10$

 

[jtran8]

That mbc looks alright to me . It,s not really that your mbc can't control at lower boost , the problem is that you already have boost creep up to 12psi ; boost controller use to turn up the boost but can't go any lower than what you already got . What i think you should do is turn your mbc all the way out , which = without mbc . now test drive it , it shouldn't go higher than before . Then turn the knob in litle bit at a time until you get boost level you want.:icon_bigg

 

[theKnifeArtist]

well thats what im sayin. the mbc is all the way out, and its boosting a lot more before. i know this because with no mbc at stock boost, once i got to like 5 to 7, the wastegate opens, and i can clearly hear it dumping below me. then it would creep to around 11ish, depending on what gear im in of course. with the mbc in and the screw loosened as much as i could, i'm clearly setting it at a higher boost, because i hear no waste untill 13-15. this is all part throttle to half throttle mind you, because if i go WOT or close to it, the boost goes up so fast that it'll hit the fuel cut level pretty quickly and that doesnt feel too good
yeah im confused too.

 

[jtran8]

If i was you , i'd port wastegate to solve boost creep problem first since you have bad boost creep , then save some money and get yourself a new or good used ebc ; control any boost level you want , you get what you pay for. Now this is not for you only but also for those who have bad boost creep ; If you have boost creep , you have to solve boost creep problem first by " porting the wastegate " then install boost controller . Boost creep is bad ,it can blew your engine at high boost level , not only that but it also cause turbo lag ( slowly spool up) down on low end power and turbo lag every time you shift to different gear . This is because your wastegate start open at lower boost level , this also call boost leaks . now if you got your boost creep fixed you only get 8psi of boost at 6500rpm on 3rd gear without boost controller ; intall ebc in and turn it to 12psi of boost , ebc will hold until it see 12psi of boost then it'll open and that's when wastegate open . A 400rwh supra with bad boost creep will be slower 1/4 mile time than 350rwh supra without boost creep. Trust me , i already done all that , feel instant power if you do it right .:icon_bigg

 

[87soup]

I have this same problem... What the heck is it???

 

[1992supraman]

how do you port the wastegate???

 

[flubyux2]

hey, im goin thru boost spike issues.

i have a double-stack of shims and no additional boost controllers. it hits 10psi immediately, then continues up to 16.5psi ultimtely at 4400rpm. then it falls off to 11psi till 7000rpm. my problem has been deemed to be the stock WG hole size is inadequate and i have to enlarge it by porting. feel free to come check out my thread in the General discussion forum too... ive listed some sizes in case any of you were curious about interrnal WG anatomy.

i wonder if i could get 16psi to hold from 4500rpm to 7000rpm by just poking holes in my WG signal hose...

 

[jtran8]

Some time enlarge wastegate hole alone is not enough . If you still have boost creep problem after enlarge wastegate hole ; make sure to check out one of my post under "( hitting fuel cut with AVCR)" I tried to help some one so I show some pictures and instruction how to port your wastegate .

 

[flubyux2]

did that car with boost creep problem still have it with the boost controller turned off? if so, what did it ultimately creep to?

mine is just spiking and then it comes down.

 

[jtran8]

Boost spike has notthing to do with boost creep ! Boost creep is because your set up efficent that wastegate hole not big enough to vent cause boost keep creeping up untill fuel cut or blew up your engine . Now boost spike is boost that suddenly go up fast and then go back down , if you have this problem you have bad boost controller ( be my guess you got mbc don't you )? replace it with ebc , this will solve your boost spike problem.

 

[buldozr]

remove your turbo and physically look at the WG hole... not much room to play with gents, maybe another mm or two due to the flapper being so close to the wall, might help, might not, I was talking with my builder at Forced Performance, he can swap out the flapper and punch out the whole but in all honesty, it is a bandade, this turbo wasnt designed to do this shit. My two cents.

 

[buldozr]

remove your turbo and physically look at the WG hole... not much room to play with gents, maybe another mm or two due to the flapper being so close to the wall, might help, might not, I was talking with my builder at Forced Performance, he can swap out the flapper and punch out the whole but in all honesty, it is a bandade, this turbo wasnt designed to do this shit. My two cents.

Also note, some of the complaints of boost creep are related to worn out waste gate actuators, keep that in mind as well.

 

[jtran8]

No need bigger wastegate flaper for ct26 . Stock flaper is more than what you need , those who still have boost creep after ported their wastegate that's because they only done half way . Enlarge wastegate hole alone is not enough to solve boost creep problem .

 

[flubyux2]

no, actually, there is a 10mm difference between the diameter of the stock flapper and the stock hole. you could easily port the stock WG hole 5mm, 8mm if you are feeling daring. DSM's "upgrade" to 34mm flappers and run well over the power level a stock CT could ever dream of. i mean, air in, air out.

also, i know the difference between spike and creep. i dont have a creep issue... my boost comes back DOWN to 11psi from 16psi. but what i was asking was, how high does that guy's boost actually GET at the top of the gear?

 

[theKnifeArtist]

so to kind of conclude with the solution to my problem...
what i did was use slightly larger diameter lines for the mbc, so that i could compensate with adjustment on the mbc.
and so it worked.
i fine tuned it to 13psi, and its been working great. Only up to 4th gear though, not 5th, that load'll spike (no pun intended) that shit right to fuel cut in an instant. Wastegate porting would be required here to solve this.
but as long as i can run out 4th gear without fuelcut issues, i'm happy for now, cus it'll finally be ready for dyno day in a week or so

 

[theKnifeArtist]

scratch that "solved my problem" thing i said. i hit fuel cut today in third gear and i'm not too happy about it. guess it was colder today than the time i adjusted it. yeah guess i need wastegate porting

 

[suprafanatic]

i just had this same problem for like 4 months and i FINALY FIXED IT!!!! mine was set for stock boost, not boost controller. and i was still boosting to 14-15psi really fast and hitting fuel cut... there are a few reasons for the problem,, 1. if you have a larger exhaust system then the car will boost more.. 2. unbolt the wastegate but keep the arm attached and push the arm and see if the flap opens, if the arm isn't at just the right angle it wont open some times so play around with it, the arm will twist some if needed. heres what i did to fix mine, i unbolted the wastegate, pulled it down, twisted is alittle and then only put one side bolted up and left 1 bolt out. i did this so there wasnt as much tention on the wastegate which obviously will LOWER the boost level. it then boosted to about 5-6psi and held there, i was happey to finaly not over boost!!! THEN i put my boost controller back on and now iam boosting 12psi steadily!!!!