I have a 98 GC 4 L. When I'm on the highway, every 20 or 30 sec. the tac jumps 1 or 2 thou. Other than that it runs fine. The oil was changed about a year ago and the level is fine. It started about a year and a half ago but would do it every few minutes. The intervals are now shorter. Would this be my transmission? Any ideas.

 

If it was your transmission the Jeep would surge whenever the tach jumps. I would have to say that it's probably an electrical gremlin. May be a loose fuse, relay or wire. Is it running well besides the tach jumping? Have you checked to see if it's showing any codes?
Just wondering but are you running dino oil in your Jeep or synthetic?

Dan

 

Yes it runs fine otherwise. The tach only jumps for half a sec.. I use synthetic oil. What fuse would you be talking about. Thanks for the reply. Also, someone once mentioned it could be my torque converter. ? And no, I have not check for codes

 

If it was the torque convertor locking up or disengaging that often you would be able to feel it and hear it, if it's just the tach I would have to say it's electrical.
Check the fuse for the instrument cluster or it could be a seperate one for the tach. Do you have a manual for your GC? It will list the location of all the fuses and relays.
But check for codes that may tell you the problem right away.

Dan

 

Thanks Dan,
It is not just the tach, I actually feel the engine rev for 1/2 sec. On the weekend I was on the highway doing 70 mph with the cruise on and it was doing it. I turned the cruise off and it quit. The only time it would do it is when I let up on the accelerator a bit and then give a little gas in a short period of time. So maybe when the cruise is on, it is constantly on and off the gas and thats when its reving that 1 rev that lasts a 1/2 sec. Thanks

 

Well If you can feel it when it happens I'm starting to think it may be one of the sensors in the tramsmission itself. It's a fairly easy job to check/ change out the sensors. If you've got a place to drop the tranny pan. Or the bands may need to be adjusted in the tranny, again you would have to drop the pan to adjust the rear band. If your interested I can PM you both procedures.
Also check for vaccum leaks around the vaccum post on the intake manifold and down by the battery.

 

Yes, please send. Thanks again for the replies. Chris