Help! boost peaks, then drops

[Marck]

I have a EA82T car with a mbc and a bunch of other modifications. It was running fine until the other day I pushed it too hard (115mph at 5-5.5rpm ). After I pulled it this hard and came to a stop, I noticed the smell of burnt oil. I wasn't worried about this because I figured it is just oil that got sucked into the intercooler draining down into the engine, thus the smell of burning oil (I need a oil catch can). I checked the oil level a few days later and found it at the min level, so I topped it off. The engine does not continue to burn oil and the dip stick still shows that the oil level is topped off.

 

The problem I am having (that started after I pushed it too hard) is that the boost will raise to the psi that I have the mbc set for, but then it won't hold. The pressure starts to drop down until it reaches stock (7psi) boost. What do you think the problem is? I figured it was something wrong with the home depot mbc that I made, so I took it apart and replaced the spring and the ball bearings. That didn't fix it. I also pulled all the intake hoses and intercooler off, drained whatever oil was sitting in the intercooler, inspected the hoses/pipes, and then put it all back together hoping that if there was a small leak somewhere in the plumbing, it will be gone after I reinstall everything. I ran the car without the mbc and it runs just fine and holds stock boost. But when I install the mbc and try to run anything higher than stock boost, I have this problem where the boost will peak and then start to drop.

[Turbone]

I'll bet its the MBC. I bought one like you made, off of Ebay and had the same situation. Either going to have to put out some money for a decent boost controller, or leave it off.

Boost is addicting, so I know thats not going to happen:-p

[Marck]

I'll bet its the MBC. I bought one like you made, off of Ebay and had the same situation. Either going to have to put out some money for a decent boost controller, or leave it off.

Boost is addicting, so I know thats not going to happen:-p

 

but the mbc worked just fine for at least 1500 miles. Can these boost controllers go bad suddenly like this even when they worked fine before hand?

[Turbone]

I think so. I assume yours is made from brass fittings? Mine was also. The brass is a soft metal and its not exactly a close tolerance unit. Even a little air getting by is going to affect what happens at the wastegate.

I fiddled with mine for a couple of weeks to no avail. I tried making a very small hole in the hose after the mbc, but ended up with full boost (fun!) and a blown HG (not so fun). I wont use another brass or cheaply made mbc again.

[beataru]

I would check for a Boost leak, my car, With all the numerous problems that it has, ok let me start over.

When My car was running sweet, I made a MBC, and it worked good, Except for the horrible boost creep that the TDO4's internal waste gate has.

Now this boost controller isnt the best choice for boosting up a car but, If it is building pressure and then drops off I wouldnt suspect the controller just yet, if you have the time, and the cents to make a new one, I would. Just to be safe of course, And its one of the easiest things to rule out.

if it does it with the new one, check for boost leaks! Remember, most of the time they wont leak under atmosphere pressures.

[Skip]

put a temp "T"ee into the line

after the MBC going to the WG

 

then connect your boost gauge to it

 

 

that will show you if it's the problem

[Marck]

I put a stiffer spring in my mbc and that seemed to have cured my problem. I see no signs of a boost leak. Thanks for all the suggestions.

[Turbone]

I did try that with mine, but it had no effect.

Looks like I will be getting a new engine from CCR soon cause a have a almost dead cylinder.

Stupid ebay MBC:mad:

Thats what I get, I guess:rolleyes:

 

Good luck with it.

[Marck]

Well, my problem came back yesterday after I did a compression test on the engine. Compression looks alright with about 100-120 PSI per cylinder. I wonder if I have a leak somewhere. I don't have time to get into it this weekend. But I'll keep you all postd on it. I will try what skip suggests about putting the boost gauge after the boost controller to see what happens.

[Marck]

put a temp "T"ee into the line

after the MBC going to the WG

 

then connect your boost gauge to it

 

 

that will show you if it's the problem

 

How does this show me if it is the problem? I did this just now. The boost would climb to 6psi at full boost and stay there. So what does this mean? The car felt like it was running at 6psi too.

 

I expected that the turbo would run to about 13psi (where the mbc is set to), then the mbc would open and the boost gauge would abruptly read 13psi. But I guess this is not how it works. Because the boost gauge is installed, once the mbc opens, the boost leaks to the boost guage instead of all of the 13psi going to straight to the wastegate? Is that right?

[Gloyale]

Well, my problem came back yesterday after I did a compression test on the engine. Compression looks alright with about 100-120 PSI per cylinder.

 

Those are kinda low compression numbers. Specs call for 150 psi. You could have some worn rings or valves.

[Skip]

If you installed it as I sugg.

 

It would read zero (0)

 

untill the MBC opens.

 

If it reads boost pressure as you say

it is installed incorrectly or

is leaking all the time.

 

The MBC is a pressure relief valve,

holding back pressure untill

the "relief" setting is reached.

 

At this point it opens and allows the air to pass.

(in this case to the Waste Gate)

 

 

I think you may have a bleed style boost control

corn-fused with a pressure relief valve

that most MBCs are?

 

The MBC goes inline between the WG and the manifold pressure.

 

If you put a Tee in the line to the WG

and connect your boost gauge to the line,

 

it should read zero untill the MBC reaches the pressure

you have it set for.

 

Comp pressures are decieving, as long as they are balanced

the gauge you use could be reading low,

I don't think this is your current problem.

[Gloyale]

[quote name=Skip

Comp pressures are decieving' date=' as long as they are balanced

the gauge you use could be reading low,

I don't think this is your current problem.[/quote]

 

I don;t think that's his problem either. I was just saying that 100-120 psi is not "good"

[Turbone]

I don;t think that's his problem either. I was just saying that 100-120 psi is not "good"

 

Not true.

A turbo engine is low comp to begin with. My readings were 100 on 3 cylinders and 75 on one. It still has torque, when the turbo spools up.

[Marck]

Went to play with it just now and found that the problem has gone away. So whatever the problem is, we know it is intermittent.

 

One thing I tried was bypassing this black valve looking thingy that goes between the pressurized intake nipple on the turbo and the wastegate nipple. What is this for/do? My mbc is installed right after it before the wastegate nipple. It also has a third hose that tees inbetween the intake (before turbo) and one of the hookups on the black canister. Originally I thought it had to do with the boost light on the dash, but then found that the light still works when this thing is bypassed, so the boost light must use the pressure switch that is next to it. So if anybody knows what I am talking about and knows what this is for, please let me know.

 

Another idea I had about the problem was that maybe the BPV on my WRX intercooler is leaking-as it is not closing all the way when it should be. Next time the problem comes back, I will trying removing the intake hose that controls it, so that it stays permantently closed.

[Marck]

I was doing some research on boost controllers and came across this on wikipedia:

 

actuator springs that are too soft can cause the wastegate to open before desired. Exhaust gas backpressure is still pushing against the wastegate valve itself. This backpressure can overcome the spring pressure without the aid of the actuator at all.

 

If this is true, this may also be my problem.

[Gloyale]

Not true.

A turbo engine is low comp to begin with. My readings were 100 on 3 cylinders and 75 on one. It still has torque, when the turbo spools up.

 

Not like a freshly re-ringed motor that make the specified 145. But I looked it up and the specified acceptable limit of 117. So I guess 100 to 120 isn't too bad

 

NA engine are speced at168, limit 139

[Turbone]

Right. Big difference between 7.4:1 and 9.5:1 comp ratio.

The reason mine is so low is because of the cheap MBC I installed. It went full boost more than once and I only had it on for a day and a half.

The headgasket was bent in 2 places, so I can imagine what the rings look like now:rolleyes:

So Marc, if this is what you want, keep using that MBC:-p

[Skip]

Listen to the man Turbone.

A cheap MBC can lead to trouble -large time.

 

As for your questions

"black valve looking thingy"

It's called the waste gate duty solenoid.

It is used by the ECU to raise boost pressure if it determines the need.

It does this in the same way a MBC does it ->

by controlling the pressure sent to the WG.

 

Disconnecting it will cause a check engine light,

but my guess is that it's on anyway or burnt out/removed.

 

You are correct the pressure switch found near by turns on the boost light.

 

With

"a bunch of other modifications"

You still have the stock downpipe and cat?

This can cause back pressure to push the WG open.

Rare but this car sounds rare => to medium.

Does not sound "well done" at all.

Get a divorced WG down pipe.

 

And

"problem was that maybe the BPV on my WRX intercooler"

Yes this can cause the boost pressure to drop if faulty or plumbed incorrectly.

 

No doubt trust a cheap MBC but find fault in a factory BPV??

 

I am wondering who built up this car.

Couldn't be you, I mean black valve thingys and bunches of modifications - ah dah??

 

Please excuse the sarcasim but my morning java isn't working yet.

I hope it stays fixed, -> we may see a headgasket thingy post next.

[TheSubaruJunkie]

When I had my RX i also got one of those cheap homedepot built MBC's. The thing didnt work for crap. Boost was all over the place, and was extremly difficult to fine tune. I think i installed it and took it off the next day.

 

I found a MBC on ebay from GoFastBits and this thing is SWEET. Same concept, just made with good parts and machined, not made from brass fittings. Ive never had a problem with boost spikes or fluctuation. I sold the RX but kept the MBC and soon it will be on my Legacy Turbo.

 

I say get rid of the cheap crap, and buy a real MBC. Do you want a $4 MBC to cost you $200 in gaskets and pistons?

 

-Brian

[Marck]

So everybody is pretty much on agreement that I should replace my homebuilt home depot mbc with one of higher quality. Besides mine being made of brass, what makes those $100 dollar mbc so much better? How does this part destroy piston rings and head gaskets as long as it never lets boost reach over what it is set for? Its the boost setting that will increase piston ring wear or if boost is set to high it may kill a headgasket.

 

To skip and others:

Sorry for not sounding technical in that last post, but the truth of the matter is that I did build this car up from a stock platform.

 

I threw the "backpressure opening the wg info" out there to see what kind of response I get. But this car does have a 3" mandrel bent divorced wastegate downpipe made by perrin and moddified to fit my car by a local welding shop. There is a 2.5" cat right after that with 2.5" piping leading to a 3" muffler. So there should be little back pressure.

 

No doubt trust a cheap MBC but find fault in a factory BPV??

I question everything. I especially question the BPV when it comes from ebay and have yet to test if it works. I know the mbc is working or at least most of the time if it is the culprit.

 

I guess I should list the mods so you guys can help me better. If we still had signatures it would be listed in that and then I can just say the car is the one listed in the signature. It gets tiring to repost the mods list everytime I post a question.

 

My subaru came stock as a GL 3d coupe with all RX equipment minus the aero body kit. Some of the mods are listed below (in random order):

1. 1. 
      
   2. All Metal Two Row CSF Radiator
      
   3. MSD Blaster High Vibration Ignition Coil
      
   4. Magnecor 8.5 mm wires
      
   5. NGK iridium spark plugs BPR7EIX gapped to 0.050 in.
      
   6. Peugeot Rims with 225/50R15
      
   7. High Volume Oil Pump by Toga
      
   8. Ported and performance valve grind on cylinder heads
      
   9. Regrind Cams by Deltacams (260 duration, .386 inch lift)
      
   10. XT Spider Intake from 87.5+ XT Turbo w/ EGR
       
   11. RC Engineering Cleaned, Calibrated, & Flow Tested Fuel Injectors.
       
   12. Custom Header by TechWorks Engineering (TWE) w/ HPC Hypercoat Extreme Coating
       
   13. Lighten XT6 flywheel from 19lbs to 15~17 lbs
       
   14. XT6 6 puck sprung (10700) clutch by Clutchnet
       
   15. XT6 50% stronger pressure plate by Clutchnet
       
   16. K&N Cone Style High Flow Air Filter with custom pipe
       
   17. Red Top Optima 800 CCA
       
   18. Autometer A/F Mixture and Boost Gauge
       
   19. RHB5 VF11 Turbo from a 91 Legacy
       
   20. modified WRX 3.0” Perrin catless downpipe w/ Jet Hot Coating
       
   21. High Flow Cat, Muffler, 2.5 inch exhaust pipe
       
   22. Heated 4-wire Bosch O2 Sensor
       
   23. Shorter Weighted Shift Knob
       
   24. KYB GR2 rear dampers with stiffer Eibach springs (8” L, 2.5” ID, 225 lbs/in spring rate)
       
   25. WRX Intercooler w/ BPV & Hood Scoop
       
   26. Man. Boost Controller set near 12~13 PSI

One correction to above, I pulled the deltacams out to pass a smog test and have yet to put them back in. So I am currently running stock cams.

[beataru]

I dont think its your MBC Mine worked great, I had boost creap but that is not the mbcs fault, its the td04s fault for having the dumbest designed internal wastegate man has ever come up with... for the most part its true that "you get what you pay for" but a manual boost controller.... how do you screw that one up... so long as its not leaking and the greedy boost hungry bastard behind the knob is paying attention, it should work fine....

Its the same thing as guns dont kill people, people kill people... Cheap MBC's dont destroy engines people behind mbcs controll engines... Expensive mbcs work exactly AND I MEAN EXACTLY as the homemade mbc does sure they look prettier but if you want to sit at the "dopy nopi nationals" then sure buy a good mbc... or hell BUY AN ELECTRONIC ONE!!! but if you want more boost... disconect your wategate... just kidding, either buy a mbc, or buy the parts and make one your self........... and boost leaks will cause the symptoms that he had... I have had tons of boost leaks, that I only found when I hooked up a smoke machine to the intake... it was so small that it only truly caused issues once my boost reached 9psi.... so end of my rambling on and on... but dont tell a man that his work of brass art sucks, it hurts real bad!!!!

By the by... I am interested in the delta regrinds, my bro in law just got his 98rs running and he had his reground... and my did he get a HEWGE LIFT!!! I can understand if you dont want to go on specific duration and lift, but are you running much bigger than stock, or just a littlebit... and how is that working for you??? I wana put HOT HOT HOT cams in my beast!!! but im afraid that I will have to build up my valvetrain to handle it (and how big did he go??? lets just say that it spit shims at hand turn with wrench speed)

[Marck]

I dont think its your MBC Mine worked great, I had boost creap but that is not the mbcs fault, its the td04s fault for having the dumbest designed internal wastegate man has ever come up with... for the most part its true that "you get what you pay for" but a manual boost controller.... how do you screw that one up... so long as its not leaking and the greedy boost hungry bastard behind the knob is paying attention, it should work fine....

Its the same thing as guns dont kill people, people kill people... Cheap MBC's dont destroy engines people behind mbcs controll engines... Expensive mbcs work exactly AND I MEAN EXACTLY as the homemade mbc does sure they look prettier but if you want to sit at the "dopy nopi nationals" then sure buy a good mbc... or hell BUY AN ELECTRONIC ONE!!! but if you want more boost... disconect your wategate... just kidding, either buy a mbc, or buy the parts and make one your self........... and boost leaks will cause the symptoms that he had... I have had tons of boost leaks, that I only found when I hooked up a smoke machine to the intake... it was so small that it only truly caused issues once my boost reached 9psi.... so end of my rambling on and on... but dont tell a man that his work of brass art sucks, it hurts real bad!!!!

By the by... I am interested in the delta regrinds, my bro in law just got his 98rs running and he had his reground... and my did he get a HEWGE LIFT!!! I can understand if you dont want to go on specific duration and lift, but are you running much bigger than stock, or just a littlebit... and how is that working for you??? I wana put HOT HOT HOT cams in my beast!!! but im afraid that I will have to build up my valvetrain to handle it (and how big did he go??? lets just say that it spit shims at hand turn with wrench speed)

 

Thank you. I don't think there is nothing wrong with going cheap with a mbc as long as you pay attention to the boost gauge. I don't expect the mbc to work flawlessly and definately not accurate or super precise, but it should be somewhat precise in that it reaches near the same max boost every time I floor it. I don't see the point of replacing a $20 mbc I made myself with a $100 mbc if it won't solve my problem that I have described in my first post. Now if my mbc is causing my problem then I will replace it with a well made high qualitly unit, but I am not going to throw more money at it only to find out that it doesn't fix my problem. The point is to make the car as fast and fun to drive as possible without sacrifing too much in reliability, longevity, and without spending a fortune on it. If I wanted to go expensive, I would have saved the few thousand I put into this car and put it down as the down payment to an STI or drop an EJ engine into the car for the ultimate subaru sleeper.

 

As for critizing one's work or car without even seeing it is just mean and it hurts. Makes me almost want to leave the board that I have been with for 5 yrs. This shouldn't be the message we are sending out. I draw my automotive knowledge from three main sources. 1. is the one year of automotive technology that I took 6 years ago in high school. 2. is this message board. And 3. is my factory service manuals. I have learned way more about cars from the threads I have read and posted on this board over the past five years more so than I can learn from 1 year of classes or any auto manual. So lets be open minded and kind to one another on the message board. It is not nice to make rude remarks by the text one types.

 

As for the expression "a bunch of other modifications" was me being too lazy to list out all the mods on the car when I wasn't sure if it was needed. As for, "black valve looking thingy," I thought I described it well when I described where each hose coming out of it was going to. I didn't know the name of the part and it looks like some kind of pressure controlled black valve. When I wrote the expression "black valve looking thingy" I was going for comedy, not the writer's engineering incompetency.

 

Back on topic, I have found that you can control the boost level with the gas pedal and still rev the engine to where you need it to shift. So you can set your mbc as high as you want and then just be causious to your right foot. If you feel the need to smoke somebody, smash the pedal all the way down so that you are running your max boost setting. If you want to take it easy on the old car, then just press the gas lightly until till you reach near stock 7psi boost and hold it there and the revs will still increase until your shift point. Heck you can even go really easy on the car and not boost the car at all and still drive it. This may sound trivial, but I mention it because I think too many of us subaru owners have gotten to use too the lead foot. Lets face it our cars, especially in stock form, are very weak in power. On a non-modified engine (turbo or NA) slamming the gas pedal to the the floor was the only way to drive and you would still be the slowest thing driving up small inclines.

[TheSubaruJunkie]

This is what i got:

 

http://cgi.ebay.com/ebaymotors/OBX-Manual-Boost-Controller-Acura-Integra-RSX-TSX-TL-CL_W0QQcmdZViewItemQQcategoryZ33742QQihZ007QQitemZ170117243530QQrdZ1

 

I still say its your MBC. But what do i know

[beataru]

MAN!! OBX makes copies of everything... I like their stuff!!!