turbo_suv

iTrader: (2)

I know there are probably a ton of misfire threads on here. I've read a lot of them on many different Subaru forums and they have been helpful in pointing me towards potential problems, but as of yet my issue has not been resolved. I've read the stickies on other forums about misfires and all the potential causes, and I've tested a lot of the potential causes, spent a lot of money doing so, and the car still misfires and idles rough. It throws a CEL and the cruise light flashes. The codes are consistently specific cylinder misfires (1 and 3 I think) and multiple cylinder random misfire.

I made a video of the car running. The video may not have turned out very well as my phone doesn't pick up the engine noise as well as it picks up the ambient noise and the sound of my voice. The video may not show much, so I'll explain a bit as well as post the video.

VIDEO

EXPLANATION
The car misfires at idle and has hesitation issues at about 70% load in high gear (4eat tranny, so 4th gear on the highway) from about 2200 to 2700 rpm. The car makes good power, and runs great up top. Leakdown was 0. Compression was a little low (I forget the numbers right now), but they were all consistent.

So far I've replaced coil packs, throttle body (TPS was giving odd values), cleaned the MAF, tested the MAF (car shuts off when unplugged), unplugged the o2 sensor (front one) to put it into open loop which didn't help. I also replaced 2 injectors as 2 injectors were dirty. More injectors may be dirty but 2 extras was all the shop had. I looked at the PCV valve and it has no visible leaks. I need to clean to the cam sensors just to rule them out. I may replace the crank sensor (CPS). I haven't tested the knock sensor.

I've been told it could be valves, either a bent valve or valve lash (valves too tight), but again leakdown was 0 and the car does make power, so I don't know if I'm convinced that its valves, yet. Maybe someone can tell from the video if the valvetrain sounds a little noisy? The car runs a little rich at idle (according to one of the mechanics who has worked on this car) but gets decent mpg (23+ highway at a good speed). My mechanic was worried that maybe the ecu was bad because when he replaced the throttle body all the values looked good and no codes came up. It was only when I took the car on a long drive several days later that problems arose, and this was after I had driven the car around locally for a few hundred miles without issue.

I am thinking:

bad cam or crank sensor
fuel filter
fuel pump going bad
bad ecu?
valves too tight?
????

I'm stumped and I would really appreciate some help.

EDIT: I should add more info about the car:

2005 Forester XT
120k miles
Timing belt done
Rotella T6 oil, Subaru filter
STI intercooler
Cobb replica catback
Everything else on the engine is stock

turbo_suv

iTrader: (2)

UPDATE: I'm going to try removing the screens under the banjo bolts for the AVCS system. I guess the TSB applies to 2004 (which is part of the reason I bought an 05) but in reading more it seems as though cars after 2004 have them as well. It seems easy to pop off the bolts so I'll probably do so just to check to see if that could be the problem or part of the problem.

02RS25

iTrader: (9)

First thing you must do when diagnosing a misfire is perform a cylinder compression and leakdown test. if low on compression, do a leakdown to see if any intake, exhaust, or piston rings are leaking air. both hand in hand, will test one side of misfire problems (compression). The second and last part you should replace are parts (plugs, injectors, intake, valves, piston rings, etc) I hope i was some help as i vaguely understood your first post. Goodluck bud!

CatchMyDrift

iTrader: (5)

What's the fuel pressure at idle?

Queen Jade

I have an 08 XT and I just got finished chasing a misfire problem myself. It wasn't just one specific part failure, it was a combination of things that were contributing to the problem:

1 coil pack
2 exhaust valves were not seating correctly
worn piston rings (lot of blow by/oil in the cylinders, rings were at the very edge of barely spec)

I replaced the entire shortblock (upgraded to an STI block) and replaced the pistons with forged CP pistons, new bearings, redid the crank, had the valves checked and reshaved to seat properly and replaced some parts:

starter
battery
spark plugs
coil pack (cylinder 2)

I've done a lot more to do it than whats been stated, but nothing that immediately pertains to the scenario so I'll skip that part. Since I've done all this work, I haven't had the misfire and I'm about 250 miles into break in. The way I was able to figure out which cylinder was misfiring was by plugging in my Cobb AP and looking at the Live Data and reading which cylinder had a rough idle. If not for that, I wouldn't have known otherwise.