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XJ Bucking.. Doesn't happen very often.. No codes, idles fine.. WTF?!

drunkmike

NAXJA Forum User
Location
MD
have actually had this problem a few times before when it was VERY cold out but I would not call it bucking.. It felt more like a slipping clutch or something along those lines.. Cap/Rotor/Plugs/Wires all replaced and the throttle body was cleaned and it only happened 1 time after that in the past few weeks. Today I left work, ran some errands and sat in the Jeep with it idling for about 20 minutes while I did some paperwork and what not. Left the parking lot and everything seemed fine. I got a few miles down the road and went to shift into third gear and the Jeep started bucking and popping.. I did not try to force it in third gear as I was at the bottom of a hill getting ready to go out so I let it slow a bit, dropped into second gear.. back up through third at partial to wide open throttle and no bucking. It did not do it anymore for the rest of the 20+ mile ride home.

A friend of mine is a Jeep tech at a local dealership and brought home the giant black computer thing for plugging into the OBD2 and scanning codes / adjusting stuff (sorry I can't remember the name) after we did the tune up and there were no codes and he went through every possible menu he could and came to the conclusion that the Jeep was running perfectly. No CEL or anything. Where should I start? This is my DD so I really can't have it go off the road and I don't want it to leave me stranded.. Ideas?

Its a 96 XJ with a motor from a 98. 6 inches of lift, 33's.. stock gears.. No motor mods other then a homemade intake that has been on there for for a long time. I have no temp gauge as of right now because the new head/motor does not connect to the old gauges.. New sender is on its way to put somewhere so I can have a temp gauge back.. Motor idles fine and normally runs great.. She is a bit groggy sometimes pulling hills but I can't blame it with 33's and stock gears right?
smile.gif
Also it has never stalled on me during any of its episodes.. Help me out@! Sorry for the long post!
 
Tom_T&Js_Offroad said:
i had a similar thing happen. turned out it was just the fuel filter...

No kidding.. The first few times it happened to me (more like slipping then bucking) it happened with around 1/4 tank of gas so I was starting to wonder the same thing.. Today It was well over a 1/2 tank. How hard is a fuel filter to do on these things? The XJ has been "with" me for over 4 years but it has just recently been turned over as mine so I have not done too much wrenching on it besides the suspension :)

It was my GF's XJ but she just wasnt driving it like it needed so I had to take over :)
 
Mine does the same thing, fuel filter didn't change a thing for me 6 months and not a single "Expert Technician" or anyother shop i have brought it too can figure out why it does this.
 
94XJ2door5speed said:
Mine does the same thing, fuel filter didn't change a thing for me 6 months and not a single "Expert Technician" or anyother shop i have brought it too can figure out why it does this.

Does yours do it often or is it kinda random how it happens?
 
Mine bucks randomly, too. I replaced my CPS, ballast, alternator(easier than I had thought), battery, fuel filter, coil, wires, plugs, rotor cap, and I have come to the conclusion that my fuel pump is propably shot. So, when I get the money, I will remove the tank, have the tank hot-tanked and coated, replace the pump, and buy a new filter. The previous owner loved to have the fuel light come on and stay on for as long as possible. I might also try a high altitude CPS since I live @ 4800'. New O2 sensors are probably needed, too. But not before the Seafoam.

That's what I have done/will do. I hope this helps a little. Good luck with your problems.
 
Mine is constant at 2000rpm and only at that specific rpm but it really really sucks.
 
I see.. Mine is very very random.. At first it was only when it was extremely cold outside (0-15 degrees F) and on a cold start + drive, but today it was a good 50+ degrees outside and the Jeep was definately warmed all the way up.. I guess there is really no definate way to tell other then to start fixing stuff piece by piece huh?
 
Speaking of idle air control valve--just recently I noticed that when I let off the throttle real fast the RPMs will dip below normal idle rate and almost cut out--is this controlled by that valve?
 
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