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Thread: Intermittent P0303 2007 Impreza Sedan 2.5i

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    Intermittent P0303 2007 Impreza Sedan 2.5i

    About 3 months ago my CEL came on with a P0303. At the time I did not notice any misfiring. I read the code and reset the computer. A couple days later, the SEL came on again and this time I noticed a slight misfire. The P0303 code was set, again.
    I determined that a P0303 relates to my cylinder #2 which is driver side front cylinder. (third in firing order)
    Lately, the CEL has been coming on about every time I drive. The misfire and roughness is quite noticeable but generally cease when at normal driving speeds. I actually drove from Benson, Arizona to Mesa, Arizona, twice without the CEL coming on. I usually need to reset the codes everyday if I want to use cruise control. Now consistently misfires at low rpm under power but smooths out at highway speeds.
    Here is what I have done to identify the problem:
    (I did 1, 2 and 3, at the same time)

    1.) Swapped spark plugs wires between #2 and #4.
    2.) Swapped fuel injectors between #1 and #2.
    3.) Swapped spark plugs between #2 and #3.
    4.) Cleaned MAF/IAT Sensor with MAFs Sensor cleaner.
    5.) Cleaned throttle body with throttle body cleaner.
    6.) Replaced ignition coil.
    7.) Performed very close inspection of coil primary wires and connectors and #2 cylinder FI wires and connector.
    8.) Inspected wires and connectors for the crank position sensor and cam position sensor.

    Still getting the P0303

    As I am on the road about 1400 miles from home, I have not been able to to do any compression testing. However, the spark plugs all look to have the same wear characteristics. A good clean look with no oil evidence. And for the most part, it runs very smooth and has great power. . It uses about one quart of oil every 2000 miles. There is evidence of a slight leak in the center of the car near the transmission area.

    My next step is to pull up the carpet and inspect the connectors at the ECM.

    If anyone is familiar with a similar situation please, give me a shout with your suggestions.

    Thank you!!
    Donald Lesicka

    1995 Impreza Wagon; 2.2 liter automatic
    2006 Outback 2.5 liter automatic
    2007 Impreza Sedan 2.5i 5-speed manual
    1995 Fleetwood Flair Motor Home on Ford F53 Chassis

  2. #2
    Administrator rkrenicki's Avatar
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    So, just to throw this out there.. P0303 is about Cylinder 3.. not Cylinder 2. The engine codes refer to actual cylinder number and does not have anything to do with the firing order. You need to be looking at the right side (passenger since you are in america) rear cylinder.

  3. #3
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    Thank you. I will now T-S the actual #3 cylinder rather than the the 3rd in firing order. I was searching another Subaru forum and was told that it was the 3rd in the F-O. I'll post the results. Thanks.
    Donald Lesicka

    1995 Impreza Wagon; 2.2 liter automatic
    2006 Outback 2.5 liter automatic
    2007 Impreza Sedan 2.5i 5-speed manual
    1995 Fleetwood Flair Motor Home on Ford F53 Chassis

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    It helps to troubleshoot the correct cylinder

    Thanks to rjrenicki, I was able to determine that my #3 cylinder (not #3 in order, but actual) had a bad plug wire. PROBLEM SOLVED.
    Thank You rj.
    Donald Lesicka

    1995 Impreza Wagon; 2.2 liter automatic
    2006 Outback 2.5 liter automatic
    2007 Impreza Sedan 2.5i 5-speed manual
    1995 Fleetwood Flair Motor Home on Ford F53 Chassis

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