Misfire from Injector Wiring/Circuit

Discussion in 'KJ General Discussion' started by Taylon, Nov 2, 2019.

  1. Taylon

    Taylon New Member

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    2007 3.7L w/ around 190k

    Cyl 5 misfire started a couple months ago, was intermittent and not as noticeable, popped random multi misfire code, along with cyl 5 misfire code.
    (replaced coil and plug, problem nearly went away for a little bit and came back.)

    started to pop the same codes again as well as an open injector/ injector circuit code, and it would go from not misfiring very badly from work and back to misfiring badly and shaking past 1500 rpm in 3rd or 4th later on when i go elsewhere from home, and this would be the same case every day for the last 2 weeks.
    (changed injector fuse, asd fuse, and switched asd relay with rad fan relay which seemed to fix the bad misfiring and bring it back down to the slight misfiring.)

    besides this i tested the old injector fuse with a test light and would not get any power, although all other fuses did, and i also tested the plug/wire going to injector 5 and got no light, however that seemed to be the case for the properly working injector wires as well.

    This makes me think that it is something to do with the wiring, relay, fuses, or pcm resulting in poor fuel mixture and some sort of electrical problem causing everything to happen. i have plenty of freeze frame data stored but i am not a mechanic so i cant read it lol.

    Long story short, f Chrysler and their electrical issues. Anybody have the same issue and have any knowledge to share?
     
  2. Taylon

    Taylon New Member

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    to add a little more, all the injector plugs seemed to have previously shorted, but then again that doesn't help me in any way.
     
  3. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Bill - Help ! I'd like to hear what Bill our electrical guru may say about this thread.
     
  4. Billwill

    Billwill Full Access Member

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    OK first thing is to buy a cheap Digital Multimeter if you do not already have one.....a test probe is very limited in its capability.

    The 2007 KJ Service Manuals are pretty much impossible to get hold of but the 2006 Jeep KJ Service manual will probably be close enough although the colors of the wires may be different...I doubt they made any major changes to the 2007 KJ when they knew that the KK was coming out soon.

    Use the Multi meter to test that if you get voltage on one side of a fuse then you should get it on the other side as well. If power is not present at either side, remove the fuse and check that it is not blown by means of the Ohms setting on the meter..make sure you are not touching the meter ends when measuring resistance of any circuit as your body resistance going through the meter leads screws up your reading.

    The Multimeter will help you trace breaks in the wiring, shorts to ground or to other wires but cannot track fast pulse such as the firing of an injector.

    So download the 2006 Jeep KJ Service Manual here...section 8W has the wiring index and the main header page has the DTC index at the bottom of the list. Find your DTC codes there and if you are lucky the page that you are directed to will be the right one for your code......what Code do you get that directs you to cyl #5 and are you counting the cylinders correctly? The various theory of operations sections give a reasonable overview of how all parts of the Jeep work.

    Jeep KJ Service Manuals: www.colorado4wheel.com/manuals/Jeep/KJ/

    Will give you a hand once you have the Service manual and Digital Multimeter!;)
     
    Last edited: Nov 3, 2019
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  5. Taylon

    Taylon New Member

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    Thanks for the info, will definitely be using it tomorrow, however it would be easier if I could explain the issues properly, at this point it has to be the injector wire, pcm, or either the wiring going to the fuses/relay
     
  6. Billwill

    Billwill Full Access Member

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    Yeah unlikely to be wiring going to the fuses as the coils and the injectors all share the same wire picking up +12 volts from shared fuses. The grounds do the switching so each coil and injector has each own wire so there a bad wire or shorting wire would be a likely suspect.

    These individual wires can be measured through from point to point and for shorts to ground but with an intermittent error you could get the break or short only when you go over a bump in the road for instance. In this case the suspect wire has to be cut off at both ends and replaced with a new wire.....been there done that about 10 times!

    So initially you would need to swap a suspect injector/coil with a working one to see if the misfire moves and then test the wiring as above.

    Could also be a mechanical problem with that cylinder but I would suspect that would be a more consistent misfire.
     
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  7. Taylon

    Taylon New Member

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    Defininitely will be replacing the wire soon, also the "bump in the road" gives me a few ideas... mainly because it acts alot worse if I dont let it cool down before starting it back up again from full heat. However it definitely isnt mechanical.
     
    Last edited: Nov 10, 2019 at 1:22 PM
  8. Taylon

    Taylon New Member

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    Just tested the injector wires and the fuse for dc voltage, for some reason they where all getting .17-.18 volts including cyl 5... shouldn't they be at 12ish ?
     
  9. Billwill

    Billwill Full Access Member

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    You need to test for +12 volts on the Pink/Gray wires for the Fuel Injectors and for +12 volts on the Red/Orange wires for the Coil Packs while the ASD relay is energized ie. with ignition ON and engine running.

    So the ASD relay needs to be in good condition ie. good inside contact and good connections of the relay pins inside the relay socket.

    Connector C104 pin 3 feeds this +12 volts to the coils while pin 2 of C104 feeds +12 volts to the injectors.

    Check where C104 is located in the Component Index in section 8W of the diagrams and re-plug this connector a few times in case of bad connection.

    All these above points are unlikely to cause the misfire only on Cyl #5 though.

    So on page 8W-30-19 Coil On Plug #5 is a Dark Blue/Yellow wire going to the PCM connector C2 pin #2. This lead may have a bad connection at either end or may be shorting to ground intermittently.

    Likewise on page 8W-30-19 Fuel Injector # 5 is a Brown/Orange wire going to the PCM C2 pin # 5 and likewise may have a bad connection either end or an intermittent short to ground.

    Re-plug PCM connector C2 a few times.

    If you still have an intermittent misfire you need to first cut off the Dark Blue/Yellow wire at both ends to isolate it. Cut the wire an inch or two from each end and insulate both ends. Replace the this cut-off wire with a new wire. Solder it to the short cut-off sections and insulate it.

    Test if problem is now resolved.
    If not resolved put the original wire back in place.

    Do the same procedure now for both ends of the Brown/Orange wire from Injector #5 going to C2 on the PCM.

    If the above does not fix your Cyl # 5 misfire then I am out of ideas for now!:(
     
  10. Taylon

    Taylon New Member

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    tried plugging c2 in a few times and it seemed to not do much, couldnt find c104 at all but I will definitely be rechecking the cables this weekend and potentially be soldering new ones in, if all else fails i guess the mechanics the only way to go.. i very much appreciate the help, have a nice one :)