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Old 12-10-2012, 09:48 PM   #1
Narclopse
Scooby Newbie
 
Member#: 269203
Join Date: Jan 2011
Chapter/Region: TXIC
Location: The Woodlands, Texas
Vehicle:
2005 WRX STi
WRB

Default Help me diagnose this

This will be a slightly long post, but I need some help on this:

Here is a little info on the car:

2005 STi
stock ECU with dyno tune
built motor - rebuilt stock heads
JE forged pistons
BC rods + bolts
ARP bolts/studs galore
bored to 100mm
cosworth head gasket

had a compression test at around 15k before I put on the rotated kit and everything was good.

motor has 19k on it with the following main mods:

GTX3076r rotated kit @ 24psi
Aquamist 100% alky injection
perrin EL headers, up pipe and down pipe
Tial 44mm EWG with dump tube
Tial Q BOV
TGV deletes
ID 1000cc injectors
perrin fuel rails
Aeromotive FPR
Walbro 255 FP
Grimmspeed AOS
Stock flywheel
ACT 6 puck clutch
No lightweight pulllies on the motor

Dyno Tune by a very good tuner - 410WHP 400WTQ - Dyno dynamics

Here is my issue that I can't figure out:

So after I got my car re-tuned for colder weather (just a tune up more or less, not to gain more power) I drove the car back home and filled up with 93oct shell like always. The next day, I was pulling out of my driveway and the check engine light comes on. I get it checked and its a cyl 3 and 4 misfire. I also notice the idle to be rough (surging), but under normal crusing and all forms of acceleration, no issues. I decide to change my plugs with NGK 1 step colders (was using Denso 1 step colders) and gap them to 24 thou, which is what the tuner recommends - I swaped the coil packs too (cyl 1-3 and cyl 2-4).
I reset the ECU and drove the car around normally. I Noticed the idle to still give me issues, but no CEL. After 120 miles of driving, the CEL came on again with cyl. 3 and 4 misfire.

If I remember correctly, at this point I refueled my car with shell 93oct and then put in a can of sea foam. - no improvement.

I then burned out about 75% of that tank and filled it back up with shell 93oct again and still no improvment.

- I think i've ruled out bad gas..

I then start to take logs at this point.

I notice that when Im at idle and first start from a stop, I get periodic misfires on all cylinders, but mainly 3 and 4. However, 4 seems to have a bit more though. When I come to a stop, the idle is perfectly normal for about 15 seconds and then starts to slightly surge and you get the occasional misfire.

I then decided to send my injectors into my tuner to get flow tested and cleaned. Cyl. 2 and 4 injectors were slightly lower than the other 2 injectors, but were still good.
Anyways, the cleaning got them all back to flowing the same. I put the injectors back in (all same cylinders) and i still have the same issue with the CEL.
The idle seems to be slighty better (still surges), but the tuner did send me a map to raise the idle to 1000rpm too.

I have taken logs and sent them to the tuner - AFRs normal, no knock at all, no misfires under normal driving or full power, no white smoke under boost etc.
At idle though, my wideband (and stock front 02) seem to jump around a little much (due to surging though..).

I should also add that when im crusing and im holding a constant speed at low RPMs (1-2.5k) the car feels not so smooth and you can feel it miss sometimes. However, anything beyond the lower RPM range is just fine and the car runs with out issues.
I just ordered a new fuel pump and install kit so I could also get another filter, but if this does not fix it, maybe the front 02?

I don't think it could be a damaged motor? I would see signs of lots of blow-by, loss of power, starting issues, etc.. I dont have any of those though.

What else could this be?
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Old 12-10-2012, 10:00 PM   #2
cowboy_Rob
Scooby Specialist
 
Member#: 194062
Join Date: Nov 2008
Chapter/Region: MAIC
Location: Camp Hill PA
Vehicle:
2003 Impreza WRX
PSM

Default

Look for a vacuum leak. Vented bov or recirculated? Any intake/maf changes
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Old 12-10-2012, 10:10 PM   #3
Narclopse
Scooby Newbie
 
Member#: 269203
Join Date: Jan 2011
Chapter/Region: TXIC
Location: The Woodlands, Texas
Vehicle:
2005 WRX STi
WRB

Default

Quote:
Originally Posted by cowboy_Rob View Post
Look for a vacuum leak. Vented bov or recirculated? Any intake/maf changes

I have looked briefly for vacuum leaks, but will do that more. I have a vented BOV. No intake/MAF changes, but I will say this:

I replaced my Perrin FMIC core with a brandnew one right before this happened, after my tune. The only difference in the two intercoolers is that the old core has an inlet (hotside) that matches the diameter of the hotside IC piping - which is smaller than the new syle..

The new style core has an inlet pipe that is the same size as the exit pipe. I called Perrin to confirm this difference, because I then had to buy a transition coupler from them to match the pipe to the intercooler inlet.

I told my tuner about that and he did not think that would cause the issue..

Hopefully I explained that well enough lol.
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Old 12-10-2012, 10:25 PM   #4
geronimo81
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Member#: 154586
Join Date: Jul 2007
Chapter/Region: BAIC
Location: San Ramon
Vehicle:
1996 Turbo Outback
9psi on 91 No EM

Default

I might look at the grounds; particularly the negative battery cable to make sure everything is tight and free of corrosion.
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Old 12-10-2012, 10:46 PM   #5
Narclopse
Scooby Newbie
 
Member#: 269203
Join Date: Jan 2011
Chapter/Region: TXIC
Location: The Woodlands, Texas
Vehicle:
2005 WRX STi
WRB

Default

Quote:
Originally Posted by geronimo81 View Post
I might look at the grounds; particularly the negative battery cable to make sure everything is tight and free of corrosion.
Yeah battery is about a 9 months old - have had it off and on a lot during all this work lately. I'll double check all that, you never know..

I'm stumped, because the car drives perfectly normal otherwise..

I've had vacuum leaks before and it just made the car run lean - fixed them quickly. The car is not running lean either..Coolant temps are 190ish at all times..
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