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96 Jeep Intermittent stumble on acceleration

Discussion in 'Repairs, Maintenance, Help' started by MarkT, Sep 3, 2020.

  1. MarkT

    MarkT Active Member

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    I have a 96 Jeep Grand Cherokee Laredo, 96k miles, 4.0 engine, automatic, 4wd. Last Saturday Aug. 22 it started to stumble, buck and hesitate on acceleration. Not all the time but intermittent and has been doing it since. I used the key to bring up codes on the dash and none. I put on a scan tool and no codes.

    It had a bad oxygen sensor, the one after the catalytic converter.
    Since this started 12 days ago i replaced the sensor with an OE one, removed the throttle body and completely cleaned the throttle body and idle air control motor, replaced the gas cap since the other one didn't always click and filled the tank and added 2 small bottles of Chevron Techron, absolutely on difference at all.

    Last year the crank sensor went bad and i also changed the grommets, elbows and hoses out of the valve cover. If it would throw a code i could narrow it down but I'm stumped. Any help, advice, directions, suggestions would be appreciated since I'm at a loss.
     
  2. ImperialCrown

    ImperialCrown Moderator
    Level III Supporter

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    If it stumbles and bucks, it may eventually set a misfire fault code, it just may not have gotten there yet. There is an OBDII Readiness monitor misfire counter screen that will show which cylinder(s) and a misfire count on a capable scan tool. This is useful when a misfire is suspected, but unconfirmed.
    Are the spark plugs OK and are the correct Champion RC12LYC Copper Plus? Platinum and Bosch plugs can cause misfire issues.
    There is an old TSB # 18-03-97 for sticking exhaust valves. Chrysler went to a stiffer exhaust valve spring and wanted us to decarbon a hot engine. See attached.
     

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  3. Gerry G

    Gerry G Well-Known Member

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    When you replaced the crank sensor, did you use an OEM one? Note the crank sensor is responsible for detecting misfires and if it is failing it may not be able to set a misfire code.
     
  4. AgentSkelly

    AgentSkelly Active Member

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    I had something similar with my old 94 XJ, which while uses a different PCM setup, I know the O2 sensors are the same. I had replaced my O2 after it failed, then about 2 weeks later, same thing happened, did warrently replacement at NAPA, but the counter gal said it looked like my wiring was melted, she oddly enough, owned a 95 and said the O2 sensor wiring comes off the bundle for the rest of the fuel injection system and see if its too close to the header; sure enough, I found out the O2 sensor male end had wiring that was exposed. Fixed that with a splice and voila, no more issues!
     
  5. MarkT

    MarkT Active Member

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    I appreciate the responses. My post may be a little confusing so to clarify. The crank sensor is from NAPA, it has 2,303 miles on it. The Jeep does put up codes. When the downward oxygen sensor went bad i got codes on the dash and tool. That was honestly bad for a few months so when this started it was the 1st thing i changed. This is the sensor after the catalytic. The sensor itself actually came apart when i was taking it out.

    I disconnected both battery terminals for a day to clear things. No change.

    The plugs have 51k miles on them. The wires, cap and rotor I'm almost certain are all factory original so after Labor Day a fresh set of Champions along with a quality set of wires, cap and rotor are going in. I'll do a compression test also and post the results.

    The crank sensor was a nightmare to change because of the location so I'm hoping its not that.
     
  6. LouJC

    LouJC Well-Known Member

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    On ours I always had to change the plugs when approaching 30,000 miles due to a slight highway speed misfire so if you are doing that and the cap and rotor I think you should see improvement. Also, Jeeps tend to do better with factory sensors such as the O2 sensors and others. Aftermarket does not always work on these and it is well known that plat plugs cause misfires. Copper is a better conductor but they do not last as long....
     
  7. LouJC

    LouJC Well-Known Member

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    51,000 miles on copper plugs is about 25,000 too many! At least in my experience with the same vehicle.
     
  8. MarkT

    MarkT Active Member

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    Just an update since they may help someone with a similar problem. After the initial work i put in new Champion plugs, premium wires, OE cap and rotor. The rotor tip was actually worn down a little. No change. I did a compression test and the lowest cylinder was just over 120 pounds. The thermostat was bad since late last winter so in went a new thermostat.

    On the test drive to the other house the problem was still there. When leaving finally a check engine light. Code 21 was code p0135, the other oxygen sensor. The wiring was all good so in went the other sensor. It had the code lurking in there for a while. Don't know why it took so long to come up but after a week and a half no problems.
     
    ImperialCrown likes this.

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