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Discussion Starter · #1 ·
Hey guys so some random new issues my jeeps been having, here's some background: I have a 1999 tj 2.5l, manual, with 170k on it. The transmissions stock. but the engine has 4 hole injectors, AFE magnum cold air intake, oversized throttlebody, dynomax cat-back exhaust. I've already changed out the TPS sensor, MAP sensor, IAC sensor within the past 2 years.

So I was offroading yesterday in the snow and when I went to help someone I ended up almost getting stuck myself. I ended up on a hill sideways at probably a 10% grade when I had to reverse down and straighten myself out because I could not gain traction and just started sliding down the hill. When I got to the bottom of the hill I got out to yell at the guys at the top of the hill when My jeep randomly shut off while it was idling. I hopped back in and the jeep started right up and the engine light flashed. There was a little hesitation, but I didn't think much of it and I ended up getting out of there. I had about a half tank of gas, so I thought it was probably fuel starvation. I also want to note I have a fuel cell in the rear with a newer fuel pump which is 2 years old, I ran the gas lines underneath the rear drain hole along the frame next to the tranny. When I looked underneath yesterday the skid plate was stuffed with snow, so I pulled most of it out the best I could.

So the next day, I'm driving to work, i'm about 30 miles into a 40 miles journey going 55-60mph going down hill and my jeep starts horribly shaking, jerking, and sputtering, like it was misfiring and the engine light came on. At this point the jeep had been warm for awhile but it was still cold outside probably like 25-30 degrees. When it jerked the rpm's immediately rev'd up from about 2800 to 4000 before I immediately down shifted to fourth. It was fine for a brief second and then started shaking, jerking, and rpm jumping again. This happened until I put it in 2nd gear. I pulled over, shut the jeep off and started it back up. It immediately did it again until I was going about 30mph and then stopped when I got it into 4th gear. Then every time I put the jeep in 5th it would slightly sputter, and act like it was gonna do the jerking and sputtering again. Naturally I refused to put the jeep in 5th and drove to work in 4th gear. I then was able to get home later by not driving the jeep over 50 and by staying in 4th gear. I tried putting it in 5th once and it started sputtering like it was going to start doing the jerking thing again

Also When I was driving home I had an OBD hooked up and I was trying to catch the engine code but nothing. But I did notice that when I shifted from 4th to 5th gear the ignition advancement seemed off. By like a lot, It was at 22- 30 degrees for 4th gear but when I shifted it into 5th it immediately went from the idling 16 degrees to like 36 degrees or more.

Talking to my dad he thinks that some how water got into the fuel or its bad gas or something. From reading online people are saying its either the distributor and the plugs, the fuel pump, the crank position sensor, or the upstream O2 sensor. The upstream O2 sensor is probably 7 or 8 years old. Before I start replacing random sh** everywhere, does anybody have any input, or have had something similar like this happen? I wasn't having ANY problems idling or running the jeep before this. I just took it up to AOAA (north of rausch creek) last week and had no problems at all driving it for 8 hours total there and back. I know I'm not the only one who has had issues sputtering like this so anything helps! Thanks
 

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Discussion Starter · #2 ·
In case anyones wondering, I was able to figure it out. It seemed to just be the O2 sensor for right now. I took the jeep out a few days later and drove around with my OBD II hooked up. While I was driving in 2nd or 3rd there was slight shaking and struggling from the engine/tranny. When watched the voltages and other stuff, I noticed some weird stuff going on by the fuel system. So the OBD will recognize if the systems in closed loop or open. When I shifted into 5th gear, almost every time the fuel system would go from closed to open and the voltages for the upstream O2 sensor would start going crazy. The O2 sensor as it warmed up would sputter going from 0.16 volts to .81 volts and then back down to .01. It was obvious at that point the O2 sensor was the issue because at a constant load the voltages were no where near each other.

So I replaced the Bosch that I had in there with a NTK O2 sensors, and I haven't had any issues since. The jeep has its power back and no longer sputters. If anything else happens I'll update again, but I'm pretty sure it was the culprit.
 
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