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Thread: Check engine light code p0303

  1. #1
    Got Beer airforce26yrs's Avatar
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    Default Check engine light code p0303

    The code is for #3 misfire. I am going to change the plugs as they have probably 50,000 miles on them and just over a year in use. I was wondering if I should change the coil pack rail also. 218,000 is a lot of miles.

    Don't know if I want to change the coil pack. $179.00 at NAPA. Ouch.
    Last edited by airforce26yrs; 04-03-2009 at 13:02.
    I'm Mike, make sure you spell it right, because I do not want to get the wrong A$$hole in trouble.

    If you do not have time to do it right the first time, how do you have time do do it over?

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    Junior Member devilnutz's Avatar
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    I would start small and work your way to the rail, you dont want to spend it if you dont need to .
    Change plugs if that doesnt help try changing the plug boots before you go for the rail.

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    Got Beer airforce26yrs's Avatar
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    Quote Originally Posted by devilnutz View Post
    I would start small and work your way to the rail, you dont want to spend it if you dont need to .
    Change plugs if that doesnt help try changing the plug boots before you go for the rail.

    The boots are part of the rail itself, as far as I know. They come of with the rail. I never really looked to see if they can be changed.
    I'm Mike, make sure you spell it right, because I do not want to get the wrong A$$hole in trouble.

    If you do not have time to do it right the first time, how do you have time do do it over?

    www.jeepforum.com michiganmaveric

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    Junior Member MACH04TJ's Avatar
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    Here are the possible problems:

    INTERMITTENT MISFIRE
    VISUAL INSPECTION
    IGNITION WIRE
    (F42) ASD RELAY OUPUT CIRCUIT
    ENGINE MECHANICAL PROBLEM
    IGNITION COIL
    COIL CONTROL CIRCUIT
    SPARK PLUG
    CHECKING FUEL PRESSURE
    CHECKING FUEL LEAK DOWN
    FUEL INJECTOR
    INJECTOR CONTROL CIRCUIT

    If you would like a copy of the FSM troulbe shooting proceedures I can email them to you.

    Mat

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    Got Beer airforce26yrs's Avatar
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    Quote Originally Posted by MACH04TJ View Post
    Here are the possible problems:

    INTERMITTENT MISFIRE
    VISUAL INSPECTION
    IGNITION WIRE
    (F42) ASD RELAY OUPUT CIRCUIT
    ENGINE MECHANICAL PROBLEM
    IGNITION COIL
    COIL CONTROL CIRCUIT
    SPARK PLUG
    CHECKING FUEL PRESSURE
    CHECKING FUEL LEAK DOWN
    FUEL INJECTOR
    INJECTOR CONTROL CIRCUIT


    If you would like a copy of the FSM troulbe shooting proceedures I can email them to you.

    Mat
    Thanks, but no problem, I have the FSM, got it when I bought the Jeep, just haven't got to look at it yet. The code went away when I started the engine the very next time and has not come back yet.
    I'm Mike, make sure you spell it right, because I do not want to get the wrong A$$hole in trouble.

    If you do not have time to do it right the first time, how do you have time do do it over?

    www.jeepforum.com michiganmaveric

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    Junior Member xjaymartin's Avatar
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    I had the same code pop after a radiator hose blew on me. I found a TSB 1803103 that addressed the issue for one of the reasons you can have a P0303 come up. Has to do with how gases escape from the catalic converter.

    I was having rough engine idle after restart following the hot soak. Are you experience any of this or a rough idle? I looked into getting the shield that the TSB said to replace, but they could not find it. I replaced the plugs and cleared the code and it's never come back. Plugs I took out needed changing, but were in overall good condition.

    I found during my research the coil pack is good for a "long time", but you do have a lot of miles on it. Hope that helps.

  7. #7
    Got Beer airforce26yrs's Avatar
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    Quote Originally Posted by xjaymartin View Post
    I had the same code pop after a radiator hose blew on me. I found a TSB 1803103 that addressed the issue for one of the reasons you can have a P0303 come up. Has to do with how gases escape from the catalic converter.

    I was having rough engine idle after restart following the hot soak. Are you experience any of this or a rough idle? I looked into getting the shield that the TSB said to replace, but they could not find it. I replaced the plugs and cleared the code and it's never come back. Plugs I took out needed changing, but were in overall good condition.

    I found during my research the coil pack is good for a "long time", but you do have a lot of miles on it. Hope that helps.
    I will have to look into the TSB as I to have a rough idle sometimes when restarting after a short stop. Thanks for the info.
    I'm Mike, make sure you spell it right, because I do not want to get the wrong A$$hole in trouble.

    If you do not have time to do it right the first time, how do you have time do do it over?

    www.jeepforum.com michiganmaveric

  8. #8
    Member warthog_cj7's Avatar
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    Another option can be a bad spark plug, resistance failure. The wife's was throwing P0305 (cyl 5). I swapped the wires to see if wire or plug. Same cylinder w/ issue. Replaced plug (champion), no problems since. It was intermittent, not constant code.

    I think your kind of rail, the coil pack services 2 plugs each. You should be able to remove 2 and just swap their positions on the rail. If the code moves to another cylinder, then it's coil related, if stays on cylinder, it's plug related.
    Dan M.

    '85 CJ-7, 4.0L,T18,4.10s,35s,Fully locked,winch,cage

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