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Old 11-29-2008, 12:05 PM   #1
stirs25
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Default Ej20k power loss above 3-4k rpm.

I searched and I'm getting too many potential answers... so I was hoping someone can narrow it down in light of my limited subaru knowledge...

I have GC8 with swapped sti ej20k motor. Everything was running just fine until last oil change (changed it to 20w50--just had it left over from my rx7). during the oil change, I took out the o2 sensor and tried to blow out the built-up carbon with compressed air...

right after that, I noticed engine lost noticeable power up at top (above 3-4k rpm). boost is holding at 15psi according to my gauge and powerFC tracing. I don't have wideband or fuel pressure gauge.

I thought maybe it was due to the thick oil, so I changed it back to 10w30 or 40 synthetic, but still having power loss issues.

I'm thinking it's not the leak since the boost is holding... I'm also thinking it's probably not hte injectors since it happened right suddenly after the oil change/o2 sensor dusting...

there's no smoke or coolant loss, so i don't think it's gasket.

i did notice that my bov was sounding little differently than before (has unusually longer hissing sound by around half a second longer--nothing anyone else would notice but me)... but i don't think it's bov leak since boost is holding and problem persists even after i changed the spring to 30psi spring...

any ideas? thanks in advance. i've been driving it for about 2 months now with no issues other than the power loss. yesterday check engine light came up for just one second while i was WOT around 4k rpm. everything is still working fine... i just wanted to ask here before i cracked it open.
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Last edited by stirs25; 11-29-2008 at 12:11 PM.
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Old 01-01-2009, 07:51 PM   #2
stirs25
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anyone?
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Old 01-06-2009, 06:50 PM   #3
racerjon777
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EJ20K powered.

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Clogged cat?
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Old 01-07-2009, 10:52 AM   #4
kheff46
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you could've got oil on your O2 while using compressed air to blow it off. giving intermittent or faulty signals. from your post this would be the first to check out. definately can throw a CEL with a funked O2 sensor.

a clogged cat would cat similarly, yet would overall have less power and wouldn't "run out" through the revs at all.

a MAF would have hesitations and or faulty idle/rev up issues

plugs and wires,cap,rotor,coil packs, etc. would act kinda like a plugged cat having less power all the way around due to insuffecient spark, ground out, etc. but could be one only one cylinder also instead of multiples.

if you had a scanner, i'd say plug in and read your O2's, injector duty cycles, knock values and see what could be causing it or happening because of it.

good luck man! keep us posted to the fix.

--keith
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Old 01-07-2009, 05:50 PM   #5
Norcalrallyist
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I would suggest if the only two things you changed were you oil and messing with your o2 sensor that maybe its your o2 sensor. Im not sure why you would start looking else where if you noticed the problem immediately after you did those two things. Good luck
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Old 01-31-2009, 09:24 AM   #6
1995REX
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my 1995 WRX is having similar problems its bone stock with about 70,000 miles on it and anything over 4 thousand it falls flat on its face came back from inspection and they said everything was good by the way mine is a RHD dont know if that will help us narrow the problem
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Old 02-01-2009, 12:48 AM   #7
sniper512
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Same thing here 93 JDM WRX. Power loss is around 3500-4000. Sometime it pulls hard though other times its got nothing. I changed my coils and it helped but the problem is still present.
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Old 02-01-2009, 05:03 AM   #8
1995REX
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hey talked to a friend of mine with a silvia said he had the same problem but it was his fuel return line so im going to look into and see what it does ill keep you updated also i noticed with mine it falls off faster and sooner the harder i drive it like once its up to temp the first couple pulls its good but then after like 3 or 4 pulls it wants to just die quick let me know if yours is the same im gona take it into the shop tomorrow and see what they say mine is still under warranty

Last edited by 1995REX; 02-01-2009 at 08:52 AM.
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Old 02-01-2009, 12:36 PM   #9
sniper512
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It sounds the same as mine. After I did the 02+ coil conversion it got better, but it still feels like it has no power sometimes above 3500rpm.
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Old 02-01-2009, 06:35 PM   #10
1995REX
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sniper is your WRX a RHD as well and if so where are you located im trying to figure out how to get my RHD back to the US right now any ideas on this as well as our current issue
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Old 02-01-2009, 06:42 PM   #11
Matt Monson
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You could have a MAF that is starting to die. Or if you've got the boost turned up and a bunch of mods you could actually max out your MAF.
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Old 02-01-2009, 06:54 PM   #12
1995REX
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well the last owner must have done that also i had a good hard pull in 4th gear the other day and it blew the hose off the turbo i was wondering if it was boosting to much but im a diesel mech by trade so its a little different to me is there a way to check the MAF
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Old 02-02-2009, 01:21 AM   #13
1995REX
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i just put a boost gauge in mine today and it drops power at 18-20PSI boost as well that is the same time the car hits about 4000 RPM wonder if its an over boost issue car is all stock to my knowledge any other ideas.
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Old 02-02-2009, 03:24 AM   #14
sniper512
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Its not stock hitting that boost. Stock should be 11-14.5psi. You could possibly be hitting fuel cut from overboosting. Is the power loss sudden throwing you forward? If so its most likely fuel cut. My issue is that the car just sometimes doesn't have the power it normally has. I have had many possible fixes thrown my way. I was hoping for a more definitive answer. So far it could be:

-A boost leak(check none)
-MAF
-Knock
-O2
-octane(U8 ECU, I am running 94 octane)
-plugged cat

Anything else I should look at lol. It seems like many people have had this type of issue. I am leaning towards the MAF or CAT myself. I just hate wasting money.
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Old 02-02-2009, 04:51 AM   #15
1995REX
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hey just picked up a Fuel Cut Defender (FCD) STD by HKS it seems to have eliminated my problem but i also picked up a boost control not installed yet so im going to work that threw the week also how do you check for a vacume leak maybe thats part of the problem with my high boost pressures o yeah its a hard fall off in power it jerks you forward in the seat for sure ill keep you guys informed when i get the boost to an acceptable level. im thinking 15 PSI
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Old 02-02-2009, 11:32 AM   #16
sniper512
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15 or a bit lower should be good. I am running 14psi right now all stock except a Catback.
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Old 02-07-2009, 01:46 PM   #17
jay_parot
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hey plz lemme know i have same problem !!!! when boost hits at 4 o 5thou rpm does same thing dunno what to do !!!
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Old 02-07-2009, 08:00 PM   #18
sniper512
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A fuel cut problem or a power loss?
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Old 02-08-2009, 12:32 AM   #19
sniper512
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Okay so my problem is back. I now believe that any time I reset the ECU the car runs fine for a bit longer sometimes other times it last one a few minutes. In any case eventually the car just doesn't pull when in boost but sometimes it pulls good like normal. What changes after a reset? Does the EUC have to relearn the timing and A/F and throttle. It just makes no sense how it runs fine then not good all in a sudden.
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Old 02-08-2009, 02:17 AM   #20
ProjectL
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Sounds a little like a problem another member had a while ago. Cam sensor I believe it was.
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Old 02-08-2009, 02:30 AM   #21
1995REX
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well mine is still in the shop here in japan as soon as it comes out ill let everyone know what my diagnosis from the doc is and maybe you can apply the same things to yours and we can all be happy with the new found performance
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Old 02-08-2009, 01:31 PM   #22
sniper512
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That would be sweet. Also is the cam sensor the same on a EJ22 Legacy in the USA or is there a donor car for it here?
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Old 02-08-2009, 07:34 PM   #23
sniper512
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I did the ECU reset by plugging the green and black connectors and following this procedure: http://www.saxonfields.freeserve.co....e.htm#_Sensors

After driving for a short time the engine light flashed 4 long and then 2 shorts maybe 3. So I am assuming code 42 or 43. This would be the idle switch/circuit or the throttle switch. Assuming these codes work for MY93? Would this be the throttle positioning sensor? Could it be something else, but tripping this code? Also the engine light never comes on while the issue is present.
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Old 02-09-2009, 07:32 AM   #24
1995REX
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Well they sent mine back with minimal work and so far so good ill give her a good run in the morning to make sure shes good and tight but they said all they did was replace the blow off valve and fixed a vacume leak more info after the drive to work at 0500 no traffic = play time
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Old 02-09-2009, 08:05 AM   #25
sniper512
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Interesting. I was leaning towards a possible BOV failure. I will try swapping this with a friends valve tomorrow.
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