Boost drops to 0 psi @ 5K RPM in 3rd (4EAT)

skid542 · Post by **skid542** » Fri Apr 24, 2009 4:08 am

If it were a faulty boost control solenoid then the MBC would have fixed the issue.

I rode with Todd the other day and this is by far the strangest issue I've experienced.

The car pulls strong right up to 5k and then instantly the boost drops to 0psi and the car quits pulling and RPM's quit rising. The motor still runs great - sounds good, no missing or stumbling. It's like the perfect soft rev limiter. But if he starts a run at part throttle it holds boost and accelerates right through the trouble spot.

What I don't get it is why something, seemingly electrical, would be temperature sensitive? I've been racking my brain over this for the last few days and haven't come up with anything definative.

I'm thinking somehow maybe the fuel is getting limited? Did you pump in a high pressure/flow pump before all of this?

I'm grasping for ideas with that one though.

asc_up · Post by **asc_up** » Fri Apr 24, 2009 4:21 am

Hmmm. Have you tried a different wastegate?

skid542 · Post by **skid542** » Fri Apr 24, 2009 4:28 am

He's tried a wastegate, several different BPV's (including Subaru and other Bosch's), TPS/throttle bodies, among other items.

It's probably quickest for him to list the things he hasn't changed.

wtdash · Post by **wtdash** » Fri Apr 24, 2009 4:29 am

skid542 wrote:I'm thinking somehow maybe the fuel is getting limited? Did you pump in a high pressure/flow pump before all of this?

I've been running an STI fuel pump since the swap.

Mike @ Revtronix suspects my TPS wiring due to some weird readings. I'm not sure where to start w/that....other than pull a used one from another car, and keep replacing parts.

beatersubi · Post by **beatersubi** » Fri Apr 24, 2009 6:42 am

Datalogging would be a huge help. Does the revtronix have any datalogging capabilities?

Post by **Legacy777** » Fri Apr 24, 2009 4:35 pm

In looking at Todd's logs, he's maxing out the the MAP sensor. I'm not sure if that has something to do with it or not. A bleed type check valve or similar hooked up to the MAP sensor vacuum/boost line would eliminate this as a possible issue.

Other thing I'm wondering is if the TCU has something to do with this.

beatersubi · Post by **beatersubi** » Sat Apr 25, 2009 6:55 am

Any way to try an aftermarket or non-Subaru MAP w/ the EM?

wtdash · Post by **wtdash** » Tue May 19, 2009 5:15 pm

Month later bump. ....and no resolution.

Regarding the MAP.....I had my FCD hooked up, which 'clamps' the voltage before causing fuel cut. Wouldn't that rule out the MAP as the cause? The Revtronix chip pushes fuel cut to 18 or 19 psi. And to repeat, this feels nothing like a fuel cut...it's not an 'abrupt/hit the wall' drop...it's smooth.

The TPS readings are kinda hard to read. Are they cause or effect? As stated earlier, I've swapped in another throttle body/TPS and got the same result.

The data logging I've done doesn't show anything, either.

I reinstalled the 480's/JECS MAF/and the Revtronix chip....car runs well and gets good (relative) MPG.

I replaced my IAC last nite, which appears to have fixed my idle issues, which is good news. Don't know if it matters but my harness was from a '91, which matched the plugs by the battery, but the engine and IAC were from a '93. The replacement is from a '91.

Also, replaced one of the IAC coolant hoses.

Just as I was done putting it together 'Murphy" showed up and I broke the harness side wire for the Knock Sensor- it was in very poor shape anyway. So I rewired that - I didn't use/connect the shield wire as my donor's wasn't connected either.

But NO CEL's on restart and it seem to idle better...got rid of the surging idle issue I've had....and high idle when cold.

Post by **Legacy777** » Tue May 19, 2009 6:17 pm

I am reminded of a problem my mom had on her 1990 Toyota pickup. The truck would just intermittently stall, no ryme or reason. After several different shops that couldn't find anything wrong, one of the dealerships spent the time to troubleshoot the problem. Turned out that the engine wiring harness that went back behind the engine had a crack in the insulation or something like that, which would show up intermittantly, and I seem to recall it possibly being temperature related.

Anyway, point being is that you may want to start looking at your wiring harness checking continuity on everything engine related from the point where the sensor hooks up back to the ECU.

wtdash · Post by **wtdash** » Tue May 19, 2009 6:55 pm

Legacy777 wrote:.... start looking at your wiring harness checking continuity on everything engine related from the point where the sensor hooks up back to the ECU.

Josh,
Thanks for the reminder...That's this week's project.

Td

wtdash · Post by **wtdash** » Sat Jul 18, 2009 10:29 pm

Update:

Josh/Legacy777 has been a HUGE help over the last few months, helping me trouble-shoot this issue...want to say THANK-YOU.

But as I hadn't found the problem, I decided to just run lower boost <14psi, and live w/it.

Well, I had a couple extra turbos to test and utlimately plan to run a TD05.

I installed a JDM TD04, which I think is a '1st Gen'; 2nd from the left in this PIC. (L>R - VF11, TD04, TD04L ('06 WRX), TD05-16G).

I was running 16-17psi, in 3rd gear and for the 1st time since this winter, shifted to 4th gear @ WOT (~110mph) and ....

NO Boost Drop! Temps were right about 90....so plenty warm.

I've also changed to a 45 degree airbox and made changes to vac hoses, etc.

So, was it the TD04L turbo, the hose changes, or ??? I may throw the TD04L back in just to see.

Regardless, hopefully the issue is resolved.

Thanks,
Td

n2x4 · Post by **n2x4** » Sun Jul 19, 2009 3:23 am

Wow... That's kind of weird. Glad the problem went away. I don't understand what could have caused that. Did you inspect the turbo for any problems?

wtdash · Post by **wtdash** » Sun Jul 19, 2009 4:31 am

n2x4 wrote:Wow... That's kind of weird. Glad the problem went away. I don't understand what could have caused that. Did you inspect the turbo for any problems?

Nate, I also need to say Thanks for your assistance as well!

I didn't note any play in the shafts, and everything else looked OK, but I'm no expert.

Td

ericem · Post by **ericem** » Sun Jul 19, 2009 6:07 am

so where is the map sensor that reads boost and vacuum and what reads barometer pressure ?

Post by **Legacy777** » Mon Jul 20, 2009 3:29 am

The MAP sensor is located in front of the passenger side strut tower. It reads both engine boost/vacuum & barometric pressure.

ericem · Post by **ericem** » Mon Jul 20, 2009 4:48 am

How is barometric pressure measured? Sometimes when I look at the value it goes to 750.00, if I wait will go to 751.25, then back to 750.00. Is it important or no? Otherwise the MAP does seem to be working just fine i tried unplugging the hose to it while watching boost and vacuum. Added a zip tie though for a bit of a better connection.

Post by **Legacy777** » Mon Jul 20, 2009 6:19 pm

There is a pressure exchange solenoid that switches the inlet to the MAP sensor from atmospheric to the reference at the manifold.

wtdash · Post by **wtdash** » Sun Jul 26, 2009 6:12 am

Swapped the TD04L back in w/my new 45 ° INTAKE made about five 3rd Gear pulls and it pulled thru 5k>>6k each time....

NO Boost Drop.

So, hopefully I can eliminate the turbo.

keanho · Post by **keanho** » Wed Dec 30, 2009 9:43 am

solved by my workshop ..cheers...

wtdash · Post by **wtdash** » Wed Dec 30, 2009 5:26 pm

Hi,
I never did figure out my issue.

I changed my intake setup and it went away, so I'm guessing it was a leak somewhere.

Sorry can't be more help.

Td

keanho · Post by **keanho** » Wed Dec 30, 2009 5:35 pm

[quote="wtdash"]Hi,
I never did figure out my issue.

I changed my intake setup and it went away, so I'm guessing it was a leak somewhere.

Sorry can't be more help.

Td[/quote]

no problem bro, was hoppping someone might knew ha..a lot of my friend said that the stock ecu have reached its threshold, hence i need a standalone.

brweber352 · Post by **brweber352** » Tue Jan 05, 2010 9:22 pm

First off, this is my first post since finding this website 4 years ago when I bought my legacy! I've managed to find all my answers using the search engine, that's a surprise right LOL. Thanks to everyone who has posted their questions and answers, without them my car would still be stock

.

Anyway, I saw this thread and it reminded of a problem I had a long time ago. I just posted this on Revtronix.com for someone who had similiar problems so i'm gonna cut and paste. BTW I could not find the answer to this problem when I had it, it took forever to find it.

Back when I first used a TD04 I used a 90 degree coupler to make the air intake work, this worked fine while I was running 12psi.

Later down the road I got an intercooler and a fuel cut defender and raised boost up to 16psi. When I mashed the throttle more than 50% the motor would bog and boost would fall way off. I found that the 90 degree coupler was actually sucking flat at high boost/load (this took 4ever to find BTW). I ended up cutting a 2.5'' piece of pipe at an angle so I could jam it further down the 90 coupler, short side of the angle facing the turbo and the long side facing the intake runner. After I did this I had no more problems and actually ran 17psi a couple times. The best fix is to have a metal 90 welded to the turbo. Remember that a turbo blows and SUCKS!!!

I'm not saying this is your problem but I figure it might help someone

wtdash · Post by **wtdash** » Tue Jan 05, 2010 10:03 pm

You may have answered my year old question!

I DID change my rubber elbow out for a stiffer piece AND a piece of pipe to connect the original 90 elbow to the intake when I upgraded to a 45 degree airbox this summer.

I was using a hose that may have deteriorated enough to collapse @ over 14psi.

I'm willing to bet that WAS the issue...the more I think about it.

Thanks!

Post by **Legacy777** » Wed Jan 06, 2010 5:49 am

Welcome and thanks for the great first post!

iluvdrt · Post by **iluvdrt** » Sat Jan 23, 2010 8:46 pm

I am currently working on the same issue with the same engine build. Boost stops at 5k.

I found my problem, maybe it is the same as yours. the symptoms are identicle.

The silcon pipe I am using for the turbo inlet sucks closed after 5k rpms not letting more air in. You could be choking the turbo depending on your turbo inlet. I am working on a rotated set up to allow a larger turbo inlet pipe to fit.

This problem was discovered on the dyno with the hood open so everything could be watched. 5k rolled around and I could watch the pipe get sucked closed.

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Boost drops to 0 psi @ 5K RPM in 3rd (4EAT)

Fixed?

Not the TD04L

need help