1. question regarding an engine issue

    not sure if this belongs in this thread or another, new here, so i figured i'd just post and find out. anyways, i have an engine issue. i keep getting a code 303 i think, or 103, either way its a piston misfire in the third cylinder. i was wondering if anyone has come across this before with grand cherokee's and might have an idea what the cause is. i have replaced the spark plugs and the power bar, i have put fuel injector cleaner into my tank to clean the tips of the fuel injection system. i'm not sure what this could be and i'd rather not spend thousands trying to figure that out only to spend another thousand on fixing the problem. any help is appreciated. thank you.

  2. #2
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    Re: question regarding an engine issue

    What year vehicle? Does it happen all the time or just when restarting warm engine.?


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  3. #3

    Re: question regarding an engine issue

    Quote Originally Posted by JPNinPA View Post
    What year vehicle? Does it happen all the time or just when restarting warm engine.?


    Never look down on anyone unless you are helping them up - Jesse Jackson

    2002. well the check engine light just recently came back on, i have been having this issue for a few months. at first it was just every once in a while i would hear a change in how the engine in running. now, at least as far as the other day, it happened when i restarted the warm engine.

  4. #4

    Re: question regarding an engine issue

    i should also note just in case, its a 6 cylinder engine.

  5. #5
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    question regarding an engine issue

    There are heat shields to cover injector #3

    Design Engineering 010378 Fuel Rail & Injector Cover Kit for 97-04 Jeep Wrangler TJ & Unlimited | Quadratec


    There is a TSB on this. What happens is heat from the hot engine evaporates the fuel in injector 3 causing a temporary lean condition and misfire when starting. Once gas flows through and cools the injector it stops misfiring.
    Its called heat soak



    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  6. #6

    Re: question regarding an engine issue

    now is that the only thing that could be causing this? i've even replaced the head gasket thinking that was the problem. i'll get that, once i have the money, but i want to make sure that isnt the only cause just in case this doesnt work.

  7. #7
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    question regarding an engine issue

    A simple check to verify is to note if there is no misfire when starting cold and it only ocurres when starting warm after a heat soak. Second temporary fix would be to make a heat shield out of aluminum foil. Do not tightly wrap injector 3 but form a cone around it and shield below. This cold be several layers. Temporary in the sense that the foil may cut wires or evaporate over time.
    Also verify it goes away after a few seconds if starting. If it continues after a few minutes it is not heat soak.

    Now knowing you changed a head gasket draws in questions regarding leaks. Intake leak, exhaust leak or injector leaks.



    Never look down on anyone unless you are helping them up - Jesse Jackson
    Last edited by JPNinPA; 03-26-2021 at 01:09 PM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  8. #8
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    Re: question regarding an engine issue

    If the above doesnt work post back.


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  9. #9

    Re: question regarding an engine issue

    ok so after a few days of driving around it didnt work. i put in the heat shield but i also changed out that fuel injector as well just to be on the safe side. when i first start my car everything is fine, after a while when i start i back up its like the whole engine is shaking. i replaced the head gasket a few months ago so i know its not that. what else could this be?

  10. #10
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    question regarding an engine issue

    You started with P0303
    Then answered it does happen post warm restart.

    Details are important.

    Its only when backing up or engine load?
    Idles fine but shutters above idle?
    Is it a specific pedal position???

    Any check engine light?

    Did you do the tests as recommended?

    By after a while??? Is the engine up to temp? Is it at a specific temp when it does this?

    What RPM does it idle at?


    When you replaced the injector did you make sure all o-ring gaskets came out and all went back in?

    When you did the head did the intake seat properly?
    Did you check if the head was cracked? Stamped 303?

    What make and PN plugs?

    I ask specific questions to determine cause. Each failure shows specific signs. When you change a bunch of parts it puts more factors in the equation.
    Its like the difference in math between addition and triple Riemann Sums.

    Differental of y of the slope of y when y=(r^3)/3

    Never look down on anyone unless you are helping them up - Jesse Jackson
    Last edited by JPNinPA; 04-09-2021 at 11:04 PM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  11. #11

    Re: question regarding an engine issue

    it happens both backing up and going forward but after a while it stops. it idles fine at 1000rpms just after a warm start the engine vibrates, if it does change the idle i havent noticed any change since it doesnt change my meter inside. no specific pedal position, simple once i start the car the engine vibrates as if the pistons arent in synch, one is misfiring and causing the others to try and compensate. no check engine light right now, it does come on if i drive long distance, like 20 plus miles. i cant say exactly how long is a while, only thing i can use as a frame of reference is when i went to lowes the other day. its about 3 miles, takes about 10 minutes, when i got out of lowes after spending probably another 10 minutes my vehicle stared up vibrating. so i dont know if it takes 10 minutes or if i would have happened sooner. as far as when i replaced the fuel injector, i didnt exactly. i wasnt 100% comfortable doing it considering i've never done it before so i had my mechanic do it so i dont know the manufacturer of the fuel injector.

  12. #12
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    question regarding an engine issue

    Thanks for the reply.

    Again if this shaking only happens on a warm engine start the heat shield on #3 injector should work. (TSB listed below)
    If it idles rough on cold starts only it could be other components.
    And if it runs rough all the time it could another set.
    So to verify. This only happens on a warm or hot engine start? It runs rough but smooths out after a few minutes 1-2 min? Sorry for asking many times. I know the issue is frustrating and at times even I overlook symptoms or changes when frustrated.

    Also, The engine should idle at 750 rpm. At cold starts on cold weather it may idle near 1000 rpm for 30 sec then drop back down to 750. If you constantly idle at 1000 this is another issue that may be compounding.

    The high idle is usually a leak in the intake side. A vacuum line, a loose spark plug, a leak at the injector a leak at the intake from improperly seated manifold or bad gasket.
    To find a vac leak you could slowly spray some WD40, intake cleaner, or even water around the points mentioned above. Start at the base of the Throttle body then vac lines then intake to engine then injectors then plugs. The engine idle will stumble or change when the fluid gets sucked in.


    Is the misfire still cylinder #3?

    Tsb about heat soak

    http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf


    Never look down on anyone unless you are helping them up - Jesse Jackson
    Last edited by JPNinPA; 04-14-2021 at 07:07 AM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  13. #13

    Re: question regarding an engine issue

    yah pretty much. after its been running it'll have a rough restart for a few minutes. i did do some testing to check out the idle, now i was under the assumption that the idle was when the car was running and left in park, when in that situation it idles at 1000 pretty consistently. when i drop it into reverse or drive it drops down a little bit, around the 750 range, until i press on the gas pedal. i'd really hate for this to be the case but could it be the piston itself causing the misfire? or would something like that cause other problems that'd be either worse or at least telling that its the piston and not something else. i'm just trying to rule things out, i've replaced the head gasket, had the fuel injector replaced and had the heat shield put on. the only thing i havent considered yet is the fuel rail itself.

  14. #14
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    Re: question regarding an engine issue

    Well engine on in park is ideling. That should be 750rpm all the time. In reverse or any gear with your foot on the brake should still be roughly 750

    You have no code other than P0303... no O2 sensor codes?

    What brand snd part number spark plugs did you use? What were they gapped at?
    Pull plug #3 and post up a pic of it.


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  15. #15

    Re: question regarding an engine issue

    no o2 codes, i did have to replace my o2 sensor 2 years ago but i've only been getting a 303 code. as far as the spark plug, off hand i dont remember which brand i used or the part number. i replaced those sometime last summer when i replaced my coil pack. i was having issues with my original coil pack so i grabbed a pick and pull one and of course that one was garbage as well so i bought a new one. i'll have to post a picture of the spark plug tomorrow after i get out of work, right now its a bit late.

  16. #16
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    question regarding an engine issue

    While you have it out swap plug 1 with 3 to see if the issue moves.


    Also did you spray around to detect s vac leak?


    Never look down on anyone unless you are helping them up - Jesse Jackson
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

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