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Old 08-18-2013, 05:08 AM   #1
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weird engine running problem-feels like engine is skipping...

Good morning all...I am having a problem that has gradually gotten worse over the past couple weeks. It seems that my TJ will begin bucking and sputtering when I get to around 40-50 mph. It doesn't lose power, but you can feel it's running horribly. In the begining it seemed to only happen in 4th gear, then 4th and 5th gear, but now it happens in 3rd gear as well. It doesn't happen all the time mind you, though the frequency of occurance has gradually increased. I'm at a loss as to what could be causing this. As background, I recently replaced the fuel pump, and switched the FP wiring from a jerry rigged setup the PO had wired into the fuse block to the factor wiring that seems to function fine through the FP relay. In addition, the PO removed the CAT, and has a straight pipe goning back to the muffler. Speaking of the muffler, mine did get banged up on the rear edge a few months ago, but I'm not sure if that may be affecting anything or not. Thanks in advance for any ideas you may have.

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Old 08-18-2013, 05:10 AM   #2
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4 or 6 cyl

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Old 08-18-2013, 08:18 AM   #3
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My 99 was acting like a bucking horse at times and had lost some high end power. Replaced tps and all is good. Just a thought.
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Old 08-18-2013, 03:50 PM   #4
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Beyond the normal tune up stuff, plug gap, etc it sounds like it could be the tps as ljjp10 mentioned, or something with the fuel system. Are you throwing any codes? One would think if the engine is acting as weird as you are saying, a code would be thrown.
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Old 08-18-2013, 05:52 PM   #5
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Check under your hood in the dark why? I had bad plug wires once and you could see it spark
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Old 08-19-2013, 01:30 AM   #6
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Thanks for the replies. Its a 4-cyl, and no it isn't throwing any codes, which I thought was weird too. Also, I had thought about the TPS, but I would think that with a bad TPS it would be a problem associated with a select RPM range, regardless of speed or gear. This isn't happening in N, 1,2,or R, and only in the area of 40-50 mph. Its really weird. Regardless, I'm gonna check the TPS and FP again. I did just recently put a new junk yard FP in, though the problems I was having before was different tan whats happening now.
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Old 08-19-2013, 01:36 AM   #7
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Tps would be my guess for sure...had the same thing happen to me...changed the tps and iac when I put a 4.0 tb on

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Old 08-19-2013, 03:43 AM   #8
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Don't laugh and hate to throw the thread off topic, but what's the "tps" everyone keeps mentioning. A friend had a similar problem, maybe I should have him check his tps?
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Old 08-19-2013, 04:22 AM   #9
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Quote:
Originally Posted by GKjeep View Post
Don't laugh and hate to throw the thread off topic, but what's the "tps" everyone keeps mentioning. A friend had a similar problem, maybe I should have him check his tps?
TPS is throttle position sensor.
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Old 09-06-2013, 10:46 AM   #10
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The going saga of the weird running problem

So a little update. Over the past couple weeks, whilst I had little time for diagnostics, the driving conditions described at the beginning of this thread have worsened. Though the behavior continues to be intermittent in nature, it became more prevalent in the lower gears, including very rarely in first gear. When this would happened the Jeep went from annoying to darn near undrivable. In addition, despite the frequent misfires, backfires, and engine shuddering, the truck continued to operate without the illumination of the MIL

So last Sunday, bending to your popular opinion , and seeing the logic in it, I replaced the TPS. This worked great for about 3 miles, then right back to where I started, still with no MIL code to give me further diagnostic direction. I was happy, and then sad, and during the intervening week, it has worked great for the first 3 or so miles, and then kaabam, misfire, backfire, jumpy engine operations...So I reset the PCMs adaptive memory, with little effect, and then yesterday tried to use a scan tool to see if thre were perhaps some codes that stored but hadn't tripped the MIL. Unfortunately when we plugged in my buddy's scanner into the data connector, there was no power.

So I started today thinking I would be spending my day chasing wires for the datalink connector. Fortunately when I tested it, it had good power and ground continuity. Still there is no MIL when we all believe there should have been, at least once, and yes the MIL does come on at start and then go off, just as prescribed in the manual. As such, I decided to do a little experiment, and disconnected my bank 1 sensor 2 O2 sensor. For the first few miles, the Jeep drove better, but the same as it has been, still without illumination of the MIL.

Suddenly after about 7-8 miles, the truck shuddered, and on comes the MIL. Now I was fairly certain this fault was due to the disconnected O2 sensor, I still pulled into Autozone to be sure. Sure enough, the only stored code was for an O2 sensor fault. I left the sensor unplugged and continued my errands, a distance of about 15-20 miles..

The truck is running like a champ, albeit with the MIL lit up. So I glad as I am that it seems to be fixed, I dont understand. Can anybody think of a reason why disconnecting an o2 sensor should correct the erraticness that has been driving any distance of late. I can not seem to come up with any. Thanks again for any thoughts ya'll might have....

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