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Old 06-04-2001, 08:20 PM   #1
alfriedesq
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Post Help with boost upgrade - high boost problem

I kept increasing the MBC and kept turning that screw up and up - - it kept going faster and faster

And then - it started to cut out in third gear after it reached some set point - also tripped a CEL

I had to back it up a notch and then it ran fine with no cut out

Anyone know what is casuing this and how I can disable it ??

PS - it happens about 17 psi


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Old 06-04-2001, 08:30 PM   #2
SuicidalLabRat
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The rex only maps to ~17; Are you smoking crack!? What's your EGT at 17?

SLR-
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Old 06-04-2001, 09:06 PM   #3
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alfriedesq:
You hit overboost fuel cut (like I told you you would when we spoke on the phone! ). It Subaru's way of preventing excessive overboost and potential engine damage that overboosting may cause. In my WRX it's ~19psi. Others have said that theirs is as low as 16.5psi. As far as we can tell it happens when the ECU sees a MAP sensor voltage of 4.5V for a few seconds. There may be other sensor inputs that trip it as well, but I don't think so (or at least we have not found them yet - has anyone else?). My advice to you is to leave it alone and set your boost controller low enough to avoid tripping fuel cut.

SLR:
I'm not sure what you mean by "the WRX only maps to ~17". The stock ECU goes to open loop at ~60%+ throttle position and at that point dumps more than enough fuel to keep the WRX rich at 17psi. In fact, at mid-rpms you can take fuel out at 17psi and still run a relatively rich A/F ratio (~11.5-12:1). Max EGT on my WRX stock (14.Xpsi) was 800C (1472F) measured in the exhaust manifold just after the collector before the turbo. At ~16.5psi max EGT recorded is the same as stock - 800C (1472F). It's not until max boost is increased above 18psi that EGT rises significantly hitting 850-870C (1562-1598F) in my WRX.
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Old 06-04-2001, 09:11 PM   #4
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TurboXS, great info, you're a great resource to this board. This would probably explain why my SFC is reading rich even when it's tapped off the rear O2 sensor.

My boost cutout is about 17psi. It cuts out after about 2 seconds of WOT.

I think SLR meant that the WRX can only run about 17psi before the boost cutout kicks in.

[This message has been edited by RidinLow (edited June 04, 2001).]
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Old 06-05-2001, 05:19 AM   #5
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Hey Mark you called it...

Al, I told you not to crank that boost up too high. Did you install the boost gauge as avised by me and Mark.

Back her down a little bit you should be happy with a setting somewhere in between 14-17...

P.S. Max boost should be measured at the top of third gear... Or even go to and see what the boost spike looks like..

Good Luck... turn that thing down...
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Old 06-05-2001, 10:04 AM   #6
alfriedesq
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TURBOXS

You are da man!

Thank you very much. I forgot all about that fuel cut off stuff - too much to remember. Your boost controller is an amazing product. I appreciate all your help and guidance.

The car runs very well and fast at the adjustment point right below where the fuel cut off comes into play - - my autometer says 17.5 psi in third gear

I have one question for you . . . .do you think the car could handle more boost if someone where to figure out a way to work around the fuel cut off protector - - eg. with a aftermarket CPU??? What do you think the max boost limit is with the stock engine?

Thanks for your help and guidance. . . .

PS Imprezd - I did listen to you - I put an autometer in the cup holder by the parking break - -


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Old 06-05-2001, 10:24 AM   #7
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Al, well their is something that does get around the boost cut... HKS makes it and it's called a fuel cut defencer. It's basically the hack way of getting around the factory safe limits.

But the thing is that after 17 and 18 psi the turbo is going to start running outside of it's efficiency range. Which will in turn heat up your internals, make you have very high EGT readings and in the followings... blow your ej20 to smitherins

Looks like you have become a boost-a-holic... Don't forget you have many other ways to gain power than just by turning up the boost beyond the turbos capabilities.

By the way. You are waiting on the Link ECU setup right... Once you go ahead with that, the the Fuel Cut won't be a problem anymore because you won't have the factory computer..
Take it easy...

[This message has been edited by Imprezd (edited June 05, 2001).]
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Old 06-05-2001, 10:50 AM   #8
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I think we are all waiting on that ECU

suby
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Old 06-05-2001, 10:57 AM   #9
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I don't think the stock engine is going to have any trouble handling whatever amount of boost that little turdo is going to push out. It certainly won't be very efficient boost at 17+ psi *blegh*. Regarding that, however, tuned well, I can see this engine withstanding 400hp, no problem. The tuning becomes the issue. After all my time on endyn's board, I'm not convinced that I can actually do it, though =) (or maybe I'm actually closer =) ). Seriously, though, experience and how you tune will make all the difference in the world for the car's longevity. Tuned wrong, and the thing won't last the day @ 14 psi.
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Old 06-05-2001, 11:03 AM   #10
Imprezd
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Conduit... yes.. you are right...!!!

Oh, I am not waiting on the LINK, I am waiting on the Unichip.

P.S. I miss my poor RS.
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Old 06-05-2001, 01:20 PM   #11
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I spoke with the guy from LINK USA today - he said its comming soon. . . .

At least it runs fairly strong with the MBC

If it blows up - I'll put all the stock stuff back on it and let the dealer fix it under warranty

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Old 06-05-2001, 02:19 PM   #12
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If it blows up - I'll put all the stock stuff back on it and let the dealer fix it under warranty
FYI lots of members won't like that statement.
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Old 06-05-2001, 09:00 PM   #13
Imprezd
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I guess you guys haven't noticed what his Username is..How about i Make it noticeable Al Fried ESQ.

OJ got away with murder alot of people didn't like that either..
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Old 06-05-2001, 09:02 PM   #14
alfriedesq
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Oh yeah AARON?// Why is that?

Anyway - i never let what others think quite my voice and I'm sure there are a few others lurking around who are planning the same move
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Old 06-05-2001, 09:21 PM   #15
Rexy
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Coming from someone who doesn't even know what fuel cut is, or doesn't have an EGT it wouldn't surprise me if he would try to do such a thing..
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Old 06-05-2001, 11:54 PM   #16
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Another way to get morepower within the 17 psi fuel cut limit - install a larger compressor.

TARMAC's WRX is stunningly fast with only 15-16 lbs of boost with an IHI VF22 ballbearing turbo upgrade (the same one on my RS-T), and a larger exhaust with EBC. The compressor, which is the same as on some of the older STi's, bolts right on and flows more cfm of air for the same level of boost than the stock TD04 can. The upgrade is well worth the $1,100.

That test drive was before he installed a new JCS cold air intake with filter in the inner fender and an Air/Water intercooler. I can't wait for my next ride

Larry www.ImprezaRS.com
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Old 06-06-2001, 06:15 AM   #17
Imprezd
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Just becuase someone doesn't have an EGT gauge has nothing to say about their knowlege... Rexy boy..

And I suppose your knowledge of cars, is directly proportionate to the amount of posts you have right...

Rediculous!

[This message has been edited by Imprezd (edited June 06, 2001).]
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