Early upshifting/Throttle problem

Yes, I have searched, and gone through many threads.

My problem is that when driving, my 1992 Xj with 4.0/AW4 will shift into overdrive and lock the torque converter at about 45mph, making it very hard to accelerate, and bogging the engine at about 1400 rpms. It will only downshift if I give it past 2/3 throttle, or put the shifter into "3".

When freeway driving (75mph), and I encounter a hill, It will bog down and then shift after giving it a lot of throttle, I will jump from about 2300 rpms to 3500 rpms, and will keep jumping back and forth, this really heats up my trans (I have a gauge). So I just tend to leave it in 3, a little over 3k rpms.

One other problem, is that when cold, if I give the engine throttle, it keeps the rpms up for a few seconds. If I were to raise the rpms to 1500, it would stay there for about 5-8 seconds, like the throttle is sticking.

Last but not least, once in a while if I let off the throttle when driving, the vehicle seems to be set on cruise control, and doesnt deccelerate, until I put the brakes on.

Is this possibly a TPS problem? Should I go buy a multi-meter to test it with? What type of meter do you reccomend?

Thanks

Have you adjusted the throttle control cable that runs to the transmission recently? I have a 92 4.0/AW4 and had to adjust mine it cleared up most of my transmission problems.

I have had some of the same problems, but not all, off and on while restoring the used 1987 XJ I acquired 2 years ago. I would check the mechanical linkage from the gas peddle to the throttle body for anything that could be making it hang up, including a week spring return, and clean and lube the cable joints while your at it. Also I suggest cleaning the throttle body and checking the throttle plate for free movement. Then get a low cost digital VOM (Volt Ohm meter). Many are well under $10 at Harbour tools and many other auto, electronic, and hardware stores.

Search the topics here for topics like idle speed, TPS, IAC, and Renix, to get data on correct test procedures and values for some of the sensors and wires. Then go test the grounds, wiring harness and sensor connector connections for bad connectors, as well as test the TPS itself. That should be a good start. Also check simple things like the battery connections, all the ground straps and cables for poor connections and bad or loose grounds. Might also check the EGR valve cicuit at some point too. Search EGR for the how too details here.

Good luck hunting.

Mike McGinness
South Houston, TX

Yes, this does sound like a TPS problem which is pretty common if you still have the original sensor installed. The TPS is one of the primary sensors the trans compter uses to decide when to shift, so if it's bad you 'll get erratic, late or early shifting. The tranny cable controls hydraulic pressure within the tranny and hence shift firmness. It doesn't control when shifting occurs, but if it's badly adjusted can cause sluggish shifting.

As for a meter, an analog meter would make it easier to spot bad spots as you move the TPS through the motions. If you go slow a digital meter is useable as well. Harbour Freight frequently has their cheap digital meters on sale for $3-4. Sears sells some decent ones in the $10-20 range. Key features to look for are: the ability to measure current to 10 or 20 amps; diode check is nice to have for checking alternators; a beeper for continuity checks lets you set the meter down and listen as you probe circuits; and voltage to at least 200 volts so you can use it for general household electrical. Even most el-cheapo meters have these features nowadays.