Persistent Misfire, Now What?
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This is a discussion on Persistent Misfire, Now What? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Before someone says it, I did see the misfire thread. :-) I have a 2002 WRX and it has basically ...

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    Persistent Misfire, Now What?

    Before someone says it, I did see the misfire thread. :-)

    I have a 2002 WRX and it has basically been misfiring since I bought it last year. A recent visit to the dealership led to their telling me that Cylinder 3 and 4 are misfiring. They assured me that it was a bad MAF and o2 sensor. I replaced both and it ran like a new car for half a day.

    Now, according to my newfangled OBD2 reader, just cylinder 3 is misfiring. Hoping this is progress.

    I'm happy to start buying sparkplugs etc and work through that misfire thread list, BUT I'd like to do it methodically and minimize my cost in buying new parts I don't need. Where should I start in diagnosing cylinder 3?

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    Registered User UEDan's Avatar
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    Swap ignition coil 3 with a known working one... Is 1 or 2.

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    Registered User Obeisance's Avatar
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    Out of curiosity, can you read the long term fuel trims with your OBD scantool? If you can, could you please tell me what they are and the age (miles on odometer) of your car?
    David - '05 WRX

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    I don't know if I can check it with my obd tool, I'll try tonight. The dealer told me it was 30-40% higher than it should be. Supposedly a new MAF and O2 sensor would fix this.

    Meanwhile, it has 182k miles.

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    Registered User Obeisance's Avatar
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    I ask because my car is having LTFT issues, and I wondered if they could eventually lead to misfires... but I digress.

    I expect that the LTFTs could be an indication of what kind of problem is causing your misfires. According to the misfires thread, many of the issues can be either mechanical, electrical or related to fueling.

    I expect that if there is an electrical issue (that spark is mistimed, or not happening due to bad plugs or coils), that the car may try removing fuel (compensating for what it perceives as a rich condition due to the unburnt fuel passing through to the A/F sensor).

    On the other hand, I expect that a fueling issue (due to an air leak or clogged injectors) would appear as a lean condition and the engine would try to add fuel. Bad MAF or A/F sensors would complicate this interpretation, but you've already replaced these (kind of an expensive first step, right?).

    Since your car is adding fuel, and since the misfire is only on select cylinders, I propose the following hypothesis: a fueling issue involving clogged injectors could lead to a lean condition (hence the raised fuel trim) which causes the misfire.

    If the injectors are unevenly clogged and cannot supply the same amount of fuel that the car adds for compensation to the closed loop fueling control (MAF, A/F sensor data), this hypothesis may even account for why you have misfires on select cylinders.

    This is an easy hypothesis to test: a $9 can of seafoam motor cleaner added to the fuel tank may clean the injectors and lead to reduced LTFTs and reduced misfire events. I am no expert in WRX troubleshooting, but I did stay at a holiday inn express through memorial day weekend.

    Also, I would never have believed that the LTFT issue could be solved with seafoam (seems like snake oil to me), however, I'm currently running a can of it through my car's tank and monitoring LTFTs, so I'll keep you posted. If I forget to update about this during this week, pm me or post to this thread (I'll get an email) to remind me.
    David - '05 WRX

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    It was a super expensive first step...though I was really happy to only spend $200 on parts and do it myself in a little less than an hour vs. paying them $915 as quoted.

    Sent from my XT1080 using Tapatalk

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    Registered User tirerob's Avatar
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    out of curosity which o2 sensor did you replace? hoping the upstream, the big expensive one with the proper denso(just for saftey lol) derect fit. the rear o2 doesnt do to much.
    when my friends come up, i hear, "you sold the camarrrroooh.....HOLY BLEEP A WRX!"
    Ya has that effect on me too.
    Rob

    Where did he go?? http://www.clubwrx.net/forums/builds...ll-thread.html

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    It's the one in the right front wheel well and yes, used a Denso.

    Sent from my XT1080 using Tapatalk

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    Registered User tirerob's Avatar
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    sweet....and $%#@ at the same time. i had a misfire p0300 random misfire that i couldnt track untill i burned off a tank of rotten 91. new gas station fixed my car lol.
    when my friends come up, i hear, "you sold the camarrrroooh.....HOLY BLEEP A WRX!"
    Ya has that effect on me too.
    Rob

    Where did he go?? http://www.clubwrx.net/forums/builds...ll-thread.html

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    Quote Originally Posted by Obeisance View Post
    ...Since your car is adding fuel, and since the misfire is only on select cylinders, I propose the following hypothesis: a fueling issue involving clogged injectors could lead to a lean condition (hence the raised fuel trim) which causes the misfire.
    Your logic makes perfect sense to me. Meanwhile, since we don't know whether seafoam does diddly, I commenced with removing parts from my engine with plans of swapping an injector with a cylinder that has not misfired with the idea being that if the problem is a clogged injector, the misfire should follow it. Does this make sense?

    I have been running Lucas injector cleaner through the thing for the last two tanks of gas since changing the MAF and the O2 sensor...so this happened in the face of that.

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    Registered User Obeisance's Avatar
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    yeah, and so far I'm not seeing much from the seafoam. I added 16 oz to my tank after about 130 miles on it (I get about 26 miles/gal, so that was about 11 gallons of gas + 16 oz of seafoam). Then I drove today. At the end of my morning commute, I thought that I was making progress, but by now that is all moot. I'll keep logging this, and may have mislead you in my diagnosis..

    5/30/2014 - heat of summer lowered the idle LTFT from 11-12 in winter
    A/F Learning #1:
    (airflow) g/s 0 - <5.60 5.60 - <10.00 10.00 - <50.00 50.00+
    LTFT 8.35 6.05 4.3 -3.13

    add seafoam at 130.1 miles on tank
    drive until 161.9 miles on tank, measure LTFT
    6/3/2014 - 32 (mostly freeway) miles after adding seafoam
    A/F Learning #1:
    0 - <5.60 5.60 - <10.00 10.00 - <50.00 50.00+
    7.86 0.78 2.44 -3.22
    idle freeway/cruise fueling range POWAHH

    drive until 194.5 miles on trip counter, measure LTFT
    A/F Learning #1:
    0 - <5.60 5.60 - <10.00 10.00 - <50.00 50.00+
    9.81 2.34 4.39 -3.22
    David - '05 WRX

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    Last night I swapped out all 4 spark plugs for ngk iridiums and swapped coils on cylinders 1&3. I figure if the problem moves to cylinder 1 I'll know it's the coil.

    I also poured nearly a whole bottle of seafoam into my tank with 6oz of Lucas top end cleaner. I purchased a new fuel filter but I'll wait till this tank of gas goes through it.

    Since all this, no misfires...but it's run well this long before so I'm not holding my breath.

    Sent from my XT1080 using Tapatalk

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