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Engine bogging down issue

98xjclassicmc

NAXJA Forum User
Location
AZ
Hi everyone. So recently my stock 98 classic xj with a 4.0 (76k miles on it) started having issues. It's hard to describe it but sometimes when I press the gas pedal to drive the engine doesn't respond and o could press the gas all the way down and it will not accelerate and there is almost like a popping sound that happens. Then I take my foot off the pedal and press it down again and it starts working only for a few seconds then it happens again. This usually happens the 2nd time I drive it in a day (it doesn't matter how long it sits between rides) and may the 3rd time but then it's usually fine. It started happening only with AC on then it started happening without it. It usually goes away after the jeep warms up? So I have been trying to figure out what it might be. The jeep is in absolutely phenomenal shape otherwise. The vacuum lines are perfect. I have replaced the following trying to fix it: new bosch fuel pump, new mopar fuel regulator, new mopar idle air control valve, new mopar tps sensor. I cleaned out the throttle body. All hoses and air related things are in great shape. I have also run a fuel pressure test and it was perfect before and after new fuel pump and regulator. I have asked so may people this question and they are out of ideas. I'm hoping someone has had this issue and could help me out. Thanks and hope to get some answers soon
 
I actually just purchased new o2 sensors and will install tomorrow. I will also check the coolant sensor too. I have not experienced any overheating at all since I've had it. Is it possible the fuel injectors are bad and causing this? I appreciate the feedback
 
As suggested, test the O2 sensors and the Coolant Temperature Sensor. I would also test the Throttle Position Sensor. If the sensors test weak or faulty, only buy genuine Jeep engine sensors and NTK O2 sensors. Inspect the sensor wire plugs for corrosion, and bent or pushed back wire pins. Inspect the wire harness for melted, chafed or otherwise damaged wires.
 
I actually just bought new mopar OEM TPS and IAC valve sensors. I will look at the o2 sensors and will replace them as described. Thanks
 
Would a faulty distributor rotor cause these issues? I ask because I didnt use an oem rotor when I replaced it a few months back
 
This could be remotely possible, but some sort of engine sensor issue or sensor wiring issue would be more common and more logical for the symptoms described.
 
So like once a day, maybe twice when I press the acceleration it starts to go and then at 2krpms or so the rpms start to go down so I release the pedal and when I press on it again it's fine and then happens maybe 1 or 2 more times and then works perfectly. Does this sound like a lean issue? Or a air/gas mix issue?
 
Test the already suggested commonly suspected sensors. Inspect the wire plugs and wires for same.
 
my 99 had a similar issue, 1X per start cycle at some point when i would give it gas, it would fall flat on it's face for a couple seconds then run fine after. i would shut it off, and it would do the same thing next time i started it, no codes to help diagnose either. finally my front O2 sensor went out and it would barely run, and it threw the bank 1 sensor 1 O2 code. after i replaced the O2 i never had the hesitation problem ever again. make sure you use the recommended O2 sensor manufacturer, irrc it is nkg, other O2's dont play well in our jeeps i hear.
 
So I just installed the front and rear o2 sensors and it has been riding perfect for 2 days now. Fingers still crossed but its looking good. Thanks for all the help everyone
 
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