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Old 05-23-2012, 10:36 PM   #1
99ForesterSti
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Default Help Needed- Hesitation (Rich + Misfire)

Background since many dont know: I have a 1995 Impreza with an STi drivetrain from a 1997 Japanese model (2.0L turbo, 5-speed transmission), and 2006 Forester XT rear differential. The drivetrain was previously swapped into a 99 Forester and mechanically ran flawlessly (wouldnt pass emissions though due to ECU incompatibility).

Problem: Now in the Impreza I have a strange bucking issue while accelerating lightly that goes away under hard acceleration. It is not an engine hesitation (been through that) it feels much more mechanical, almost seems like there is excess slop somewhere in the drivetrain (if I had to venture a guess its the front, possibly right side.) Also at highway speeds the same wheel (right front) will shudder momentairly while cruising or accelerating lightly (as in trying to get up a hill)

So far I have checked: Front wheel bearings, tie rods, control arms, ball joints, axles seem to have no excessive play. Rear differential back-lash was checked within specs before installation and transmission/rear differential are filled with fresh fluid

I suppose it could be excessive slop in the front differential or possibly a bad universal joint, those will get checked tomorrow. Any one have any other ideas? I need to make an 800 mile round trip this weekend

Thanks for any help guys

Edit: Figured out the mechanical issue but cant determine why it is misfiring, read below
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Last edited by 99ForesterSti; 06-27-2012 at 08:23 PM.
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Old 05-24-2012, 06:21 PM   #2
AKGC8
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Pretty basic stuff I know but I have to ask, are the rear axles seated all the way into the differential. The shaft itself would not show any excessive play, actually less than usual if it wasn't.

I'm not even sure what a loose rear axle would act like in operation. I can't think of anything up front that could be missed during an install like that.
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Old 05-24-2012, 07:23 PM   #3
99ForesterSti
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yea all the axles are fully seated into the diffs and hubs. part of me is starting to lean towards crappy engine/trans mounts or maybe it is in fact a harsh hesitation at light throttle because today when trying to accelerate it felt like it was stumbling a bit until it got over 5psi of boost

that still wouldnt explain the highway speed vibration under load though
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Old 05-24-2012, 07:50 PM   #4
AKGC8
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Pitch stop and all the mounts torqued down?
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Old 05-24-2012, 08:48 PM   #5
99ForesterSti
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yes they are torqued i just think that with the age of them they may be going bad. i mean i can lie under the car, grab the tailshaft of the tranny and move it relatively easily
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Old 05-25-2012, 03:09 PM   #6
Surb00
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Had a late model XT forester do something similar. It was one of the front CV axles came with virtually no grease and was binding. Was difficult to diagnose until the axle was out of the car. The car would shake under acceleration and at certain speeds. New axle completely solved the issue.
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Old 05-26-2012, 10:09 PM   #7
99ForesterSti
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how exactly did you go about diagnosing that out of curiosity?

noticed the car is starting to run extremely rich at idle and low rpms (low boost) which is causing a hesitation. im pretty sure its from a cracked turbo inlet pipe. that coupled with a shot transmission mount, im guessing thats my issue. will hopefully be fixed this week before STPR
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Old 05-27-2012, 03:13 PM   #8
Surb00
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It was an auto, and this was at a dealership. I knew it was driveline there were no codes for engine or trans. I removed the awd fuse, it was still there, I felt it was up front. It happened in straight line and turning, I figured the front diff had little influence. I checked the wheel bearings and suspension for slop, there was none. At this point I thought it could be the axles and I felt it was from the RF, pulled that axle and could feel the CV binding. Pulled the boot and found there was little to no grease and had the axle replaced under warranty. FWIW I would imagine the cracked inlet would be making your car run lean not rich(taking in air after the MAF). Good luck.
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Old 05-28-2012, 08:32 AM   #9
99ForesterSti
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Yes but if it is taking in air after the MAF the ECU will see constantly lean at the o2 and throw fuel at it. either way i know its cracked, that bothers me. ordering one now will see if that fixes the issue
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Old 06-17-2012, 12:27 PM   #10
99ForesterSti
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So i still have this issue. I have realized my oringinal impression of it was wrong, the bucking is from the engine misfiring and the engine/trans moving around enough to cause the strange feeling and noise.

Now to make things really weird, the issue actually went away almost completely for about 4-5 days. I drove the car ~180 miles to the STPR rally in the beginning of June, where I drove it around to a couple stages on saturday. Then on Sunday there was an SCCA rallycross event which i competed in. Now driving around saturday the issue started to become less noticable. On sunday during the event it didnt misfire one bit. After the event it drove home without misfiring hardly at all (one minor hiccup here and there, barely noticable) and continued to run smooth for a few days after i got back.

Once i had to put gas in it again though, it immediately started to misfire after i filled up. Figuring it was just a bad patch of gas (Exxon station, had been running almost completely on Sheetz gas when it was running well) i made sure to fill up at the Sheetz but the misfire got progressively worse. It got to the point where it was missing so bad that trying to accelerate from a stop became dangerous as it would take 10-15 seconds to get up to 3k rpm in first gear (pouring black smoke the whole time) Once it got up to around 3k rpm it had built ~10psi of boost and would take off and pull hard.

I changed the upstream o2 on friday and it ran much better but still noticably was misfiring and has now gone back to the really bad misfire described above. I checked the coil and wires but did not get to the plugs (they are tough to get to on these dual cam engines) The wires were perfectly good, and the coils checked out to be a touch out of spec (resistance values ~ 20% higher than the specs, 10%-15% is actually allowed for)

I am going to check the plugs themselves and also possibly do a compression test while im at it on monday, does anyone else have any ideas of what i should check? Im almost at a loss and as this is my DD currently.
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Old 06-17-2012, 12:39 PM   #11
n2xlr8n
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1) Clean your MAF sensor...carefully.

2) Use Learning View...it will tell you that your CL fueling is screwy.

Make absolutely sure you don't have any vacuum / boost leaks.

Post a log.

S.
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Old 06-18-2012, 07:50 PM   #12
99ForesterSti
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Cleaned the MAF today and put the factory plugs back in it (had replaced them with WRX BKR6EIX before dropping the motor in) Runs infinitely better now. Doesnt miss except under partial load now but even at that its much better than it was. Im assuming the plugs were just too fouled to work properly.

I am going to look into wiring in my OBD-II connector this week when i have time so i can log it with that program. Thanks for informing me of it i wasnt aware of it
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Old 06-19-2012, 02:35 AM   #13
n2xlr8n
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You're quite welcome

This forum is all about learning.

S.

Quote:
Originally Posted by 99ForesterSti View Post
Cleaned the MAF today and put the factory plugs back in it (had replaced them with WRX BKR6EIX before dropping the motor in) Runs infinitely better now. Doesnt miss except under partial load now but even at that its much better than it was. Im assuming the plugs were just too fouled to work properly.

I am going to look into wiring in my OBD-II connector this week when i have time so i can log it with that program. Thanks for informing me of it i wasnt aware of it
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Old 06-27-2012, 08:21 PM   #14
99ForesterSti
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Have not been able to wire in the OBD II connector yet but the car has begun to run progressively worse. It seems like the more i drive it in a day the worse it gets. Im convinced it is mostly a closed loop issue as it is noticibly worse when the engine warms up. Hardly made it up a small hill today in 1st gear. Im kind of thinking it is getting progressively worse over time due to the plugs getting fouled, question becomes: what is causing them to be fouled?

Having no way to read the codes/no way to mess with the tune is making this incredibly difficult.
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Old 06-28-2012, 11:47 PM   #15
az02wrx
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this might be a long shot, but i'll throw my idea in lol . i don't know if this a problem for subarus but on my wifes old bmw 328i we were having the same problem the plugs would foul and the car would run like crap. i didn't have a scanner at the time so i looked on the bimmer forums and found out the crank position sensor cause that to happen. then after i put a new sensor in the car ran a little better but still would foul the plugs, finally my dad ended up with the car and he just happens to have a 99 m roadster (it has a similar engine 3.2 vs the 328i 2.8) and we traced the whole thing to being a couple sensors being plugged in were the weren't meant to be.

i hope this well be of some help. maybe you have a bad sensor or something is plugged in to the wrong connector. good luck
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Old 06-29-2012, 11:57 AM   #16
99ForesterSti
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yea that could be a possibility, i was thinking something along the lines of ECT, or CKP possibly, leaning towards the ECT because the car definitely runs worse in closed loop (up to temp an such) And it is definitely fouling the plugs thats why it is getting progressively worse. The only thing that is making me not run out to find a new CKP is the fact tthat it still runs fine in open loop (10+ psi of boost) and the ecu uses the CKP the same in open loop as it does in closed loop (enough to partially rule it out as of right now atleast)

I changed the fuel filter last night for ****s and gigs because i have no idea how long its been in there but havent gotten to drive it yet

Last edited by 99ForesterSti; 06-29-2012 at 12:29 PM.
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