Multiple misfires, Cyl 2 & 4
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This is a discussion on Multiple misfires, Cyl 2 & 4 within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hey Everyone, Having a misfire problem on cylinders 2 and 4. The idle is really rough and I'm getting a ...

  1. #1
    Registered User Icysheet's Avatar
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    Multiple misfires, Cyl 2 & 4

    Hey Everyone,

    Having a misfire problem on cylinders 2 and 4. The idle is really rough and I'm getting a CEL on cylinder 4 (P0304) and also the CEL for the random misfire. I've tried the usual already, including swapping coil packs, injectors, installing new plugs, cleaning the MAF sensor, and installing a new fuel filter.

    I took the car to a local mechanic and he ran cranking compression, running compression, and leakdown tests getting the following numbers:

    ~130 psi for all four cylinders during the cranking compression test
    ~ 65 psi on cylinders 1-3, and 40 psi on cylinder 4 during the running compression test
    ~20% leakage on cylinder 4

    This suggested that there may be a valve problem, so I took the car to a subaru dealer in bakersfield, ca, roughly 110 miles away, and yeah, that's the closest dealer.

    The dealer performed a compression test again getting the same numbers and did a leakdown test on cylinder 4 getting only 2%. I don't know how there could be such a large discrepancy between each leakdown test performed.

    The techs at the dealer then thought it could be the ECU sending incorrect signals so they replaced the ECU, which changed nothing.

    Then they thought it was bad gas, so they are ran out the gas in the car and put in the gas they use at the dealership, again no change.

    I'm at a loss right now, they want to charge me ~$800 to open up the head to see if it really is a valve issue, but there's no guarantee that's the problem.

    Does anyone have any ideas on what to try next, I'm so stuck!

    Thanks everyone!
    2006 SGM STi Cobb Stage II

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  3. #2
    Moderator Donkey's Avatar
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    Do you have a lightened flywheel or pully? It helps to list your mods when asking for a diagnosis. Next would be de-carbonizing the motor. Search "Seafoam" or ask the mechanics about a combustion chamber cleaning. Checking the valve lash clearances. I used to get them all the time from my lightened flywheel so I just turned off the DTC's. No more CEL's for me.
    Resident Adviser @ WTF Tuning, LLC
    2002 FORESTER S
    1998 FORESTER S




  4. #3
    Registered User Icysheet's Avatar
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    Sorry about that, should've done that in the first post.

    Prior to taking the vehicle to the dealership I had a Cobb SF intake, Cobb AP, and Turbo XS TBE.

    When I took it to the dealership it had the Cobb AP and TBE.

    When they wanted to switch the ECU I drove there and uninstalled the AP.

    It now only has the TBE. Other than that it is completely stock.

    I thought about using seafoam before taking it, but ended up not using it. I don't really have a good reason for not doing it.

    Is there a way to check the valve lash clearances without taking the head off and subsequently everything in the way of taking the head off?

    I was quoted ~$800 to take the engine apart to get to the head, check the valves, fix if necessary, and then put it back together.

    I really don't mind too much paying the money if I know that will fix the issue, but their diagnosis seems to show no evidence of a valve issue. Seems like they are running out of ideas.

    If the compression is good, and there is very minimal leakage, what else would tell you that you have a valve issue causing misfires?

    I'll ask the dealer about de-carbonizing the motor before shelling out money for something that has no guarantee of fixing the problem.
    2006 SGM STi Cobb Stage II

  5. #4
    Moderator Donkey's Avatar
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    The valve clearances can be checked with the heads on the car but it's not easy due to the boxer motor layout. Most pull the motor then just remove the valve covers and check the clearances.
    Resident Adviser @ WTF Tuning, LLC
    2002 FORESTER S
    1998 FORESTER S




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