[Guest]

I need some help with transmission shifting problem. I believe, from reading posts, that it may be the tps. Anyway, my jeep will reverse just fine. When driving, it seems the transmission goes randomly from gear to gear. It goes into the gears just fine, just not the right ones. Had the tranny checked and they said it was fine. Sometimes the jeep will just quit and you have to crank it again. Sometimes it changes gears just fine. Advice is much appreciated!

I really love my 1988 Jeep Grand Wagoneer 4wd much better!

 

[tazman85305]

I believe you are confusing the TPS with the TCU. The Transmission Control Unit gets signals from all over your Jeep, so it would be difficult to diagnose it here. Quick check to see if the TCU is your problem, disconnect it. It sits under the dash on the passenger side. Reach up under the dash, find the TCU(it's pretty big, not hard to miss) and unplug the wire harness. Then take your Jeep out for a drive. You will have to shift manually. Start out in 1-2 then shift to 3 when the rpm's start to build. Shift to drive once you reach about 40.
If your Jeep runs fine, you may want to drive like this for a week or so. If your problem returns with the TCU unplugged, then obviously that wasn't the problem.
I may have the TCU wiring diagram hiding on my hard drive somewhere. So if you think that the TCU is bad, PM me and I'll do a search for it. I may have even posted it here a year or so ago so you may want to do a search for it here.

 

[tazman85305]

Found it in one of my previous posts. I hope this helps.

 

[Guest]

Greetings,

I have the same problem with my '89 cherokee. It jumps gears up and down and sometimes the lockup skips in and out. I'm almost positive that it seems to happen at a certain position of the throttle pedal. About 1/8 depressed. It never does it when I give it lots of gas - half pedal or more.

Do you think this would be related to the TPS feeding bad info to the TCU?

Recently it seems to have slippage along with erratic gear changing so I'm afraid the tranny is being damaged from this problem.

Thanks for any help.

 

[NIX]

Not having an auto but knowing the TPS on an auto differs from a manual. Auto's are double (signal to the TCU) and manuals are single. You both might be right.

 

[Guest]

I checked the TPS with a voltmeter and it reads 4.65v regardless of throttle position. Haynes manual calls for this voltage at wide open and 200 mv in the closed position. Assuming this means the TPS is bad, why wouldn't it also affect the way the engine runs and idles? It idles and runs fine. It would make sense that the tranny thinks its seeing WOT because it always seems to downshift at strange times.

New TPS is $75 - a lot if it doesn't fix the problem. Plus I have to try to adjust it. Is this done the same way by using voltmeter to set open and closed throttle at 4.6 v and 200mv.?

Thanx.

 

[NIX]

Are you sure you probed the right wires? Sounds like you probed the + and - instead of the output and -. See also the post from Tuckjaminout. Adjusting the TPS is done by turning the thing. The mounting screw holes are oval.