1. #1

    2000 Cherokee misfires in reverse & when warm

    2000 Jeep Cherokee Sport 4.0 Check engine light on shows codes Po202 and Po204. Misfires and shutters mainly when put in reverse and gas given to back up also strong exhaust smell. Also runs worse when warmed up after driving awhile. This is a recurrent issue. Put in 2 new fuel injectors (2 & 4) and new plugs but as soon as I backed up it coded again and misfired. Then I had the codes removed and reset and was told to drive some miles to clear codes. I rode ok for 35 miles now it seems to misfire worse in forward AND reverse. Wires were checked before and I was told they are ok. This is an expensive mystery I need help.
    Any help greatly appreciated.

  2. #2
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    Re: 2000 Cherokee misfires in reverse & when warm

    Welcome to jeepz.com . From your research , has it been suggested to check wiring or have you checked this on your own ? You'll want to make sure the connectors are locking well on the injectors , the terminals are not loose inside the connectors and the wiring back in the harness isn't damaged . Start from the connector and go through the harness until you reach the splice where all the injectors get their power from and look for any breaks or corroded splices. You'll want to check the ground side too but the code(s) set are pertains to power . There may not be an issue with ground which is provided by the PCM but it seems the power wires are in need of being traced for a short or possible problem in the splice from the power source .
    Never overlook the obvious . It's usually right in front of us

  3. #3
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    Have you verified the gasket on the injectors was in good shape and seated correctly?

    Might reseat the PCM connections


    Last edited by JPNinPA; 09-01-2015 at 07:11 AM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  4. #4

    Re: 2000 Cherokee misfires in reverse & when warm

    [QUOTE=JPNinPA;332543]Have you verified the gasket on the injectors was in good shape and seated correctly?

    Might reseat the PCM connections

    First of all thank you both for responding to my request for help.
    Someone has checked the wiring and told me that they did not find a problem.
    Initially the worst misfire and rough idling would happen when the Jeep was in reverse when applying the gas to back up or somewhat when the car had been driving for a while. Now since changing the plugs and 2 injectors and driving 40 miles it seems worse and even after sitting all night the car runs rough but again much worse and smells in reverse.
    I watched the video and that vehicle sounds like my Jeep sounds now with the hesitant start and rough running but there is NO smoke coming out of the tail pipe. What does it happening worse in reverse say? Where do you recommend I go from here? Thanks

  5. #5
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    Re: 2000 Cherokee misfires in reverse & when warm

    The YouTube video in JPNinPA ,s post is an excellent one as scanner danner is my mentor . You probably don't own an occiloscope so you won't be able to perform the test as per the video but you get the idea of what to look for in terms of a fault. Diagnostically , the video mentions what is a valid test and what isn't but at least a continuity test can be performed to verify if a short exists . You must unload the power circuit BEFORE you attempt a continuity check. You will have to remove the power from the circuit by removing the fuse that powers the injector circuit . When there is no power in the injector harness , the circuit can be safely checked . Be sure your checking the power side and NOT the ground side . The ground side is controlled by the PCM . Don't want to mess with that for this test. You should have a wiring diagram to better understand this circuit to know that you've removed all power from the circuit to be safe . If you have a computer safe test light , you'll know for sure your checking the right side. Usually the ground side will have a tracer ( stripe ) on the color code on the insulation of the harness plug wiring but consult the wiring diagram to be certain . If touching ground with the continuity tester and the injector plug power wire of the injector in question causes the continuity tester to light , there is a short . It's not a difficult test but please understand the fundamentals of the circuit first before attempting this test . You don't want to introduce voltage , even penlight voltage , into a live circuit . That is a no no . Always test the circuit for voltage first before doing a continuity check. Before performing this test , you really should inspect the harness to,verify visually if any damage to the harness exists. I don't know what testing was performed prior that you've mentioned and was said that the wiring is alright but keep in mind that the troubles codes still exist and are referenced to high voltage in the circuit which indicates constant voltage present due to a draw that is caused by a short. The power side of the circuit is always live when the ignition is on and the injector only fires when the PCM grounds the injector when needed but the code is set when too much voltage is found by the PCM upon grounding the injector and excess voltage feeds back to PCM. That is why a short must be looked for as that is the most likely cause of your drivability problem. You posted that it is stronger in reverse . Keep in mind that the transmission has more power in reverse than first in any transmission so,the engine is under more load and the problem will be felt more in reverse than in drive. That is somewhat irrelevant since the problem exists regardless. Bottom line is that the injector for each cylinder that the DTC fault was found on is over active . The duty cycle of the said injectors for the said cylinders is higher than the rest of the cylinders on the engine . A good multimeter with duty cycle in percent scale can find this easily. The two cylinders will have higher duty cycle that the rest . But the main test is the test for short circuit. If your hesitant to proceed citing possible error procedure wise , please let someone who knows these test procedures well to do the testing . Will respect the decision not to cause further damage. But the testing for a short needs to be performed.
    Never overlook the obvious . It's usually right in front of us

  6. #6
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    I'll have to watch again but the PCM side is the ground side of the injector. Reverse gear is lower than first gear and will load the engine more. Power is from the engine. Just to clarify.
    Last edited by JPNinPA; 09-02-2015 at 01:10 AM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  7. #7

    Re: 2000 Cherokee misfires in reverse & when warm

    I appreciate your time in answering my request for help here. Thank you both for your valuable input.

  8. #8

    Re: 2000 Cherokee misfires in reverse & when warm

    dont trust the mechanics, do it yourself. pop the hood and start the engine, then start moving wires around. look close at wires near or rubbing the engine. I would like to add that you might have a broken motor mount causing the engine to move more than normal. just saying
    1996 Cherokee Sport 4x4
    2002 Grand Cherokee Laredo 4x4
    2006 Liberty 4x2
    What can I say... I love Jeeps

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