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2002 Subaru EJ25 2.5L M/T; starts good; runs erratic; cyl #3 misfire at idle

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here 2002 Subaru EJ25 2.5L M/T; starts good; runs erratic; cyl #3 misfire at idle

This topic contains 0 replies, has 1 voice, and was last updated by Ben Ben 1 year, 1 month ago.

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    HISTORY: bought at 87 kmi and drove till 215 kmi, always used quite a bit of oil, but ran well. Then rapidly got to running very poorly until it failed to start in very cold weather (so we got a 2004 Outback A/T to drive). Next summer, I investigated and found cylinder #4 had burnt exhaust valve and all 4 cylinders had light scraping on top (#2 being the worst) and totally gummed up oil rings. I honed the cylinders & put in new rings, exhaust valves, valve seals & top-end gaskets, timing belt & pulleys, Belden spark wires & NGK plugs. Now it has 160-170 psi compression all the way around with all plugs out (faster cranking than one plug at a time on later test of #1 & #3 which was 155 & 160 psi).

    SYMPTOMS: Doesn’t run smooth at moderate acceleration and cruise—hesitation, jerky, and once warm, cylinder #3 misfires– rev it and let it settle back to idle, and it doesn’t misfire for a few seconds, but then increases to almost steady misfire.

    We’ve driven it enough now (1400 mi) to tell it only gets about 15 mpg, whereas it used to get 25 before the valve burnt.

    In the course of endless power tests (pulling the spark wires from the coil one at a time), there was twice it has switched from cylinder #3 to #2, but I could never reproduce it. The first time was when I swapped #1 & #3 spark plugs, but then in a minute or so it went back to #3. The second time was when I was testing around all over with the propane, pulling vacuum hoses &c.

    ATTEMPTS: Borrowing from the good-running 2004 AT Outback, I swapped spark plugs, wires, coil, throttle position sensor, and cam position sensor (the last two called for by error codes). I also swapped #1 & #3 injectors, checked for vacuum leaks w/propane, all to no avail. I got lots of variations in idle by opening & plugging off hoses, and feeding in propane, but nothing that indicated a leak, and no change with just the propane directed at any of the joints.

    Nothing changed the symptoms (except twice non-reproducable incidents mentioned that misfire jumped from cylinder #3 to #2 momentarily).

    OBD CODES: I don’t have a code reader so get auto-parts store to test, so that’s inconvenient and sporadic, since we’re an hour from town. There have been erratic misfire codes, but consistent codes are:
    P0122 Throttle Position Sensor/Switch A Circuit Low Input
    P0341 Camshaft Position Sensor Circuit Range/Performance
    P0447 Evaporative Emission Control System Vent Control Circuit Open
    There were misfire error codes before the rebuild (w/burnt valve) and a couple sporadic times since, but now all we get consistently is the cam & throttle sensors (and apparently non-critical) evap vent circuit.

    NOT TRIED: I would swap the Manifold Absolute Pressure sensor, but it is different on the two models. 🙁 The 2004 has it back next to the Throttle body, whereas the 2002 has it further forward where the intake manifold forks to cylinder #2. Is there a reasonable way to test it?

    I have not tried with O2 sensors disconnect, as that does not seem indicated and I’m uncertain what effect it would or should have.

    I have not tested fuel pressure, for lack of a tee, but could make/get one, but meanwhile, it’s not clear what to expect or what it would tell me, and I don’t know where the pressure is regulated. What’s the little vacuum valve on the end of the fuel high pressure line? Unplugging the vacuum had no noticeable effect.

    I heard a comment but was not able to follow up with about “Subaru’s cylinder #3 acting up. Is this a prevalent thing, and what is typically going on? Thanks for any help or ideas.

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