So, I've always been the stock boost kind of guy, I've never seen/touched/used a MBC. There are a couple of things that unscrew off mine, and it's the gauge *which has not moved....then again, I can't really see it while I'm driving!* and some ...plastic end piece. I have some pics, as I don't know what I'm talking about. *edit* this MBC came on the car. As of right now, the car is pushing ~10 PSI in first and second gear, while hitting 15 *I know, scares the **** out of me...no more WOT in 3rd!* in 3rd...don't know about 4th and 5th. That is the reason I'm trying to figure this little guy out. I think I'm getting boost creep/spike, but I don't have the skills/tools/anything to port the wastegate at this time...so I'm trying to learn as much as I can.

 

It looks like either a pressure regulator or a pressure relief valve like those used in this 2 part write up. You can control boost with either device alone, but the regulator alone will produce wastegate creep (not the same as boost creep), as mentioned.

You need an aftermarket boost gauge so you know if you're getting boost creep, and if you can't port your wastegate, tune the maximum boost to something manageable, and possibly increase intake/exhaust restriction.

http://www.autospeed.com/cms/article.html?&A=0670
http://www.autospeed.com/cms/A_0685/article.html

 

OK, so I parused the article a bit, not fully quite yet, and from my understanding is I undscrew this item just a slight bit at a time, and verify the boost is lowering.

Now, as I understand it, Boost Creep is different from Wastegate Creep....What's the difference? Now, these characteristics confuse me a bit, as the boost is different in each gear. If there was boost/wastegate creep, wouldn't it be consistent?

 

I'm not sure what you mean by "wastegate creep" either, it's not a common distinction.

If you have boost creep you need to TAKE THE DAMN BOOST CONTROLLER OUT UNTIL YOU FIX IT PROPERLY. The MBC just makes boost creep worse and more unpredictable. When it's cold all bets are off, if you are hitting 15psi now you could hit 20. You may have the adjuster set ok for a given ambient temperature, but it will constantly vary in the level of boost response and peak boost achieved as the weather changes. Trust me, I was ghetto and ran an MBC on an undersized HKS 40mm external wastegate with an aftermarket turbo. I would log the boost curve from one day to the next and the curve was always different (MBC setting was the same). All boost controllers suck when the wastegate is undersized, some worse than others.

Run a vacuum line from the compressor outlet straight to the wastegate actuator and remove the MBC. Then put some restriction in your exhaust or port your wastegate per the Aaron Cake writeup. You should be hitting a consistent 6psi boost in all gears without a boost controller if your wastegate is flowing enough. People wonder why turbo rotaries have such a reputation for blowing up... FD's are bad with boost creep too. Shitty Hitachi turbos...

 

The autospeed article refers to the wastegate opening partially before your set boost level as "wastegate creep." Air bleed and simple pressure regulator MBCs will do this, but the ball and spring design of so called "granger valves" and pressure relief valves eliminate it.

But this doesn't have anything to do with boost creeping to 15psi, I threw that in there so the OP could design himself a better MBC. That is after he gets the max boost levels back down so his motor doesn't blow up.

And another thing, get that MBC connected to something other than the boost sensor. I can only guess the previous owner set it up that way to trick the ECU into thinking it was below 8.6psi (fuel cut level). Your ECU won't adjust timing properly relative to boost levels; especially if you're seeing 15 psi . The valve should be inline with the wastegate line, and not involve anything else. But for now, remove the MBC, and run stock boost.

 

Yeah, I plan on getting a better boost controller in general *EBC if I can afford...*

Just to make sure I have this right, though. First thing I'm going to do is replace the regulator thingy with a vacuum hose, then get a smaller exhaust, then going off when I can, port the wastegate a bit. If I get the 'MBC' removed, with that start to steady off my boost, or will I need to get the exhaust done before boosting to ensure I don't blow anything?

 

1. Remove the mbc & hook up a vac line directly from the compressor to the wastegate.

2. Reconnect the boost sensor to the intake manifold.

3. Test drive the car to see how high the boost creep is taking you at WOT in 3rd/4th gear. Stock boost is 5.5psi on S4s, but your exhaust will still be overwhelming the wastegate. It might take longer to reach it, but it'll likely still hit 15 psi if you let it. Don't let it get there, if it starts to creep towards 10 psi, let off.

4. Find out what your fuel situation is. Hopefully you have larger injectors and an upgraded fuel pump. The fact that it hasn't blown yet leads me to believe you have some sort of fuel upgrade.

5. Remove that cone filter setup and stick in the stock air box to possibly restrict airflow a bit there. If your exhaust is free-flowing enough, this might not do anything at all.

6. Put a cat in the exhaust system to restrict it and reduce boost creep.

***OR***

7. Buy a S5 stock turbo to replace the S4. The S5 wastegate is almost SIX times larger than the S4 without any porting at all (13mm vs. 18.5mm + 25mm). Not to mention, the exhaust manifold is divided for better velocity and will let you get rid of the twin scroll b.s. They can be had for around $200 turbo + manifold.

 

OK, I'm liking the whole "get the s5 turbo" because the whole wastegate deal was always an annoyance to me. Now, I'm trying to get my hands on a turbo back Racing Beat exhaust. I don't imagine that will be too terribly free flowing.

1.) You say remove the MBC *which I'm going to assume includes geting the vacuum line connected from the pressure sensor to...wherever it goes..right?*

2.) Reconnect boost sensor. This is going to be entertaining, as I don't even know what it looks like/where it can be/why isn't it there right now! D:

4.) I DO need to figure out the fuel thing, but the PO said it's a Walbro 255, as for injectors...not sure. I'm going to ASSUME stock, just so I don't blow my engine in the long run *stock injectors can get me to 10 PSI safely, I believe I've read.*

I may play the dummy game of search and ask about hooking up that vac line to the compressor to wastegate, as TBH, I have no idea

 

Alrighty, I've taken out that MBC and replaced it with a straight vacuum/pressure hose. I also changed my oil *cheers* and now I am hitting fuel cut. Great! So now I know why that MBC was there. I get to about 4k RPMs before the ECU cuts me. Now I just need to get a more restrictive exhaust, and I'll be in business.

Then I can work on finding out what is leaking *and from the looks of it, it's also leaking some oil, as when I changed the oil today, I noticed a little drip from under the pan...might be the plug, or the gasket.*

*EDIT* Also, I thought the wastegate was part of the turbo! I plugged my vac line into what seemed like my LIM...I know it wasn't near my turbo! Did I just screw up?

*EDIT2* Thanks to this picture, I've learned I plugged the Pressure sensor into the Air Control Valve! Hurray!

 

The wastegate IS part of the turbo. It is an integrated wastegate design, with the actuator mounted on the compressor housing & the wastegate itself within the turbine housing. Hopefully you've got your wastegate vac lines looking like the ones in the pic I attached. Also, make sure you know that the vac diagram you posted is for S5 cars, so there are a few differences from the S4 layout. Your hookup for the boost sensor is correct though.

You said you're hitting fuel cut as low as 4k rpm. Are you reaching 8.6PSI or greater when this happens? You should still be able to get up to redline if you don't go full throttle, but at WOT, you will boost creep well above the fuel cut threshold.

For fuel, if your car has a walbro 255, but still only 4X550cc injectors, 10PSI is pushing the injectors to the limit of what they can handle. Even with a better flowing pump, the injectors will bottleneck the system. You really should take off the UIM and read the part numbers on the sides of the injectors. The secondaries can actually be read with the UIM still on. The stock 550cc Denso injectors will have the PN 195500-1370 & tan or purple tops.

 

Forgot the picture....^

 

That doesn't make sense...

The MBC cannot lower boost.
If you are hitting overboost fuel-cut after the removal, something else is wrong.


-Ted

 

^ the MBC was in-line with the pressure sensor(!)

You need to port the wastegate. Even an unported s5 wastegate probably won't do the trick, mine creeped like hell even with a small amount of porting to it.

 

Yeah, I've never taken off the UIM, so it is a scary subject for me. Any DIY's laying around for it? I figure I have the upgraded injectors, as my engine isn't blown yet, but I would like to know exactly what I have back there. I know he has a 5th injector thrown on the intercooler piping RIGHT before the intake...here is a pic.



You notice it up there on the right. I guess I could take that off and get an idea of what the secondaries are going off of, but wouldn't the stock primaries be OK, while upgraded secondaries do the trick? Or should I upgrade both of them?

During WOT, I hit the 8.6 PSI Fuel cut at right around 4k, maybe 4.2K. I haven't quite tried to get too high up in the RPM range without boost, I just took her out to warm her up, get the new oil through her system, and made sure the fuel cut exist. I guess I'll have to send out my ECU to get the RTEK chip, which I was going to do with my previous TII, or I could find another way of going about it.

1.) ding ding, thanks arghx.
2.) Well, that's the thing, if I have the turbo out, I might as well 'upgrade' it a bit, right? From what I've read, the S5 turbo's are a bit better in terms of turbo itself + wastegate, correct? OR is it all just wastegate plus?

*EDIT* I was looking around, and the S-AFC looks pretty darned good, from what I can tel. Would it be the wrong thing for me to get? Seems like it would fit like a glove for my needs.

 

Doh.
I was too lazy to read everything.
Sorry for the mix-up.

Interesting way of avoiding fuel-cut though...
It's just like what the Hondas used to do...


-Ted

 

This car is the master of surprises. Upon closer inspection of a leak, I deduce it's oil near the front. I learned that the OMP isn't even hooked up to the throttle! Wonderful. More looking...all 4 lines from the OMP are severed. GREAT! No oil into my housing. Time to premix asap. Lets hope the damage isn't severe.

 

yah......i saw that in the first pic and i didnt want to comment............changing the boost readings that the ECU sees is a big no no. get a FCD!

ive got my MBC installed in the line inbetween where the WG picks up at the hole in the turbo, and then spliced back into the WG. also have my boost gauge plugged into the MBC because it has 2 aux ports, but im thinking i should put it elsewhere, because wont it not give proper vac readings if its sitting right at the turbo?

 

This guy's father is the Rotary Doctor, so something tells me he, by genes, hates hondas :P

But a quick question. You mentioned a MBC can't lower boost. So that means the only way to limit my boost is to get a more restrictive exhaust and then port the wastegate with a SAFC Neo + EBC, correct?

 

port the WG with a neo and ebc? i r confused ahaha..

porting is a physical mod, not electric. i hope j00 know that! gotta take a die grinder and enlarge the actual wastegate hole. a neo will help with the tuning, and a EBC will only give you more accurate corrections in raising the boost. the only thing that is going to fix your fuel cut prolbem at the moment is getting a FCD and porting the wastegate, or going to more restrictive/stock exhaust.

 

I wasn't meaning LITERALLY porting it with the AFC Neo, I was saying port it COMBINED with a AFC will do exactly what I'm wanting. Sorry for being confusing *I was?*.

 

ahaha good god. i was really hoping you werent that lost. yes, the other mods should suit your setup nicely.

 

Hehe, thanks. I may be pretty dumb when it comes to cars, but I'm not THAT bad. :P

*I hope D:*

 

Yeah, that last pic you posted tells me that you've got your hands VERY full. That wiring harness looks serverely modified, especially where he wired in a 5th injector. I can't imagine doing those kind of things to my car; it make me feel sorry for it for putting up with the previous owner.

After you address the boost creeping problem, I'd tackle the task of getting the wiring back to stock. That 5th injector is positioned in an absolutely retarded location. It's BEFORE the throttle plates. All it's doing right now is flooding the system with fuel so the 15PSI spikes don't kill the motor. You're much better off using the standard 4 injectors at sizes appropriate for your HP level.

 

Yeah, this is turning into more of a project car than I anticipated...but I really don't mind. I'll fix the boost creep issue, then resolve the OMP leaking/not doing anything with a blockoff plate....the only issues I'm going to have is the search function not working like I want it to. I can search for a DYI UIM removal all day, and I doubt I'll even come close to finding one lol.

 

Question!

I'm really thinking of getting the AFC Neo. I've gotta get the more restrictive exhaust, but I feel more comfertable with a fuel controller. Now, I have no idea how it works or anything, so if I do get this item, I'll scavenge the forum here.

My question is, is the AFC Neo what I want? It's relatively cheap *375-400 bucks*. Something tells me that it will not include a FCD, so I'll have to get one of those in the future *Although I kind of have one with that MBC...*. Now, the whole reason for this is so when I get my exhaust *I'm really wanting a Racing Beat, but waiting for another used one to be sold for 300...* I'll have a way to tune the fuel which...in my crazy head means I will be mostly resolved. I'd assume that my wastegate will need to be ported or the boost spike will always occur.

Since I've never seen anything of that sorts before...does that sound about right? I'm trying to get a list of step by steps of what I need to do. This weekend is the "hopefully take off the UIM and find out what injectors I'm running" while that's the only physical thing I can do at this time, since I doubt I can take off the turbo at this time with my limited expertise. Man, DYI would rock, I should make some :P