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Old 02-25-2013, 11:04 PM   #1
Scooby Newbie
Member#: 342651
Join Date: Jan 2013
Chapter/Region: MWSOC
Location: wausau wi
94 L-sti

Cool v3 turbo lag diagnosis

I got a 95 impreza L coupe around 5 months ago and here's Whatsup . V3 1997 sti ej20k motor with fmic,koyo radiator , 3" tbe and cai d2 coilovers . It pulls hard holding 20-21 psi on stock vf23 turbo I used 93 octane used

here in wi.

After purchasing , tightened all the loose bolts and mounts , fixed notchy shifting, replaced the squeaking, slipping six puck clutch with an exedy stage 1 hd and act light flywheel, new alternator , new starter , ss uel headers and up pipe .

After finally resolving my random stalling issues and constant idle hunting in neutral by getting new iacv and having idle reset and adjusted with tps and other things , I still have some issues .. all work done has been from my neighbor and traceys auto in town so that's good . Idk why I get random cels when flooring in higher gears , and also when coasting /decelerating in those gears . the codes are still idle air codes when logged but my idle is finally smooth and not dropping to low anymore or hunting .

I did some research and figured out how to use aem true boost ebc that's installed in here and when going through settings I see that the whole time I've had this car running strong , my iwg spring pressure is set to 23.5 , and duty cycle 12% in A and 15% in B .

this thing pulls hard but has a lot of lag , it's not fully spooled pulling hard til around 4500rpm which makes it difficult to race my friends Evo 9s that spool up by 3k! Not sure how normal this is to have such extreme lag on a stock turbo with no exhaust leaks or vacuum leaks.. I even took long pulls in 3rd and 4th gear today after adjusting wastegate spring pressure to 6 psi and duty cycle to 25% and other combos but my results were either more lag and/or less boost .. I even turned it to off setting to see what psi my wg is running on and that was around 9 psi ..

I've had problems diagnosed with this cheap aftermarket bov installed by a previous owner that were found out last week and are temporarily fixed til tonite when I get my gfb hybrid adjustable bov installed and routed to recirculate 50% and be adjusted with Allen wrench maybe that could change somethings .

Idk what else to do to find out wtf is going on with this lag but it just can't be right ! I just want a reliable tune from Shane @ dbperformance in rogers mn asap to utilize all my bolt ons n such to maximize power .

Oh btw I have an apexi power fc and commander standalone I picked up used for a steal $400 but atm I'm still running my Jdm no 6 ecu til tune time . I've researched anything and everything for months with any upgrades or issues I've had and I know this is a lot of information , but hopefully ppl know something and can enlighten me ]
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Old 02-26-2013, 02:42 AM   #2
Scooby Newbie
Member#: 280926
Join Date: Apr 2011

Things you can try:

Pressure-test your intake path from the turbo through FMIC back to manifold for leaks. The many joints that a FMIC requires increase the possibility of leaks.

Check for pre-turbo exhaust leaks

Check that the wastegate flapper is completely pulled shut with the engine shut off. If you have an adjustable wastegate arm then you can shorten it to increase the pre-load on the wastegate flapper.

At what RPM in 3rd gear do you get 7psi and 14psi?

I'm not sure what features your boost controller has but if it can vary wastegate solenoid duty cycle by RPM, you could try what I use. Set a very high duty cycle in the low RPMs and then reduce it at the point at which you hit full boost. So for example if I hit full boost at 4000 RPM, I will have 80% duty cycle till 3800 RPM and then reduce that to 25% (or whatever you need to maintain target boost) at 4000 RPM. This gives me MBC like response.
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Old 03-04-2013, 11:24 PM   #3
Scooby Newbie
Member#: 182226
Join Date: Jun 2008
Chapter/Region: VIC
Location: Kelowna
1997 STi RA


I'm sure this will be no help to you with all of your mods, but I have a bone stock JDM v3 STi and it doesn't get into Full boost/power untill 4000rpm. It's a high strung engine, power comes from 4000 to redline at 8000rpm, with very little power before 4000rpm. My 05 STi had way more power low in the rev range, but less up top. You may have to brake boost if you want to run with the evos.
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Old 03-05-2013, 12:01 AM   #4
Scooby Specialist
Member#: 94268
Join Date: Aug 2005
Chapter/Region: TXIC
Location: Nolanville, TX
1995 JDM STi RA ver2
2010 Exige S240


I think it's the engine... or I need to get her tuned again.

I'm running EJ20G (closed deck) with bigger injectors and turbo (TD05H-20G). I don't hit full boost until 4-4.5k. When I had the stock turbo (TD05H-16G), it spooled pretty late too around 4k.

A totally different animal compared to the 06 STi I had back in the day, when I could get full boost (21psi) by 3000 rpm haha. Then again, less displacement and a bigger turbo so I'm not surprised.
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Old 03-05-2013, 09:27 AM   #5
NASIOC Supporter
Member#: 177
Join Date: Aug 1999
Chapter/Region: NWIC
Location: Austin, Texas, USA
The 93 W/EJ20K-sold
Subaru-less :(


eh 4500 is to high you have a leak

but 20 psi on 440cc injectors is way too high, turn the boost down

if you are going to use the power fc (there is a reason you got it cheep)
get a j&s safeguard, everyone that has a k should have one
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Old 03-16-2013, 06:58 PM   #6
Scooby Newbie
Member#: 269804
Join Date: Jan 2011
Chapter/Region: International
Location: Stgo, Chile
1997 Sti V-Limited
rally blue


i dont know if this will help you much, but i've got an sti v.ltd with a 6s stock ecu ( (apparently). When i had my stock downpipe the car used to hit boost a bit earlier, at 3100 rpm aprox. With the catless downpipe flat plate the boost come at 3500 rpm which is not bad and i get full boost around 4000-4500 rpm.when i installed my equal length header i had a similar issue, it ended up being that my up pipe had cracked and i had a pre turbo exhaust leak, boost used to come at 4500- 5500 rpm. For a vf23 turbo, that's not right. So make sure you have no pre turbo exhaust leak cos i realized after 2 months when the crack was huge.
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