jtodaro

Ok, So I've drained the fluid and replaced, as well as adjusted the TV cable.

Tranny seems correct, sometimes, when it's cold. On the highway in OD, it runs about 2150 rpms at 65-70. If I was to drop it into 3, it'd be running about 3k rpm at the same speeds.

So, odditity, sometimes (not always) when it warms up (I'd say after about 10-12 miles of continuous highway driving, is where I mostly experience it), it seems like it's not in OD any more although the gear selector says it is. It seems to be running the higher RPMs like it's in 3rd gear. I've even went as far as to gently drop it into 3 when this happens and it doesn't change the RPMs at all.

Ok, so fast forward to me getting to my destination about 12 miles away. I'll run into a store or whatnot (no more than 20 or so minutes) and poof, it drives fine again for a little while.

Anyone have any clues to check?

kjc

You might check/adjust your brake light switch. It's a multi-function switch.. besides turning on the brake lights, it's also used to unlock cruise control (if equipped) and iirc it disengages the torque converter lock-up. Just a guess.. good luck!

may pop

Any codes?

jtodaro

No codes at all.

cruiser54

This is not just a guess. It's good advice.

jtodaro

But would the brake light switch cause it to shift down from OD on the highway and be in 3rd, until it cools down? I'm leaning more towards a TCU issue.

cruiser54

Is it shifting from OD to 3rd or OD with lockup to unlocked torque converter?

jtodaro

Seems more like OD to 3rd, as I can downshift (with the shifter) into 3rd without any affect on RPMS (as well as it also seems to match the RPMS perfectly that I've normally seen from 3rd at that speeds).

cruiser54

When in OD for sure, lightly tap the brake pedal and see what happens.

jtodaro

Either it just wasn't happening today (maybe cause it was 10 degrees cooler out than previous days), or I was mistaken before. I can tell you that based on some RPM calculations/situations I have noticed that it looks like what I was experiencing before was that after some warmup (about 12 miles or so), the tranny would just stop locking up in OD, but was still in OD it seems.

Assume this will be TCU related, but could also be TPS?

I wasn't experiencing the non-lockup today, but I did lightly tap the brake while still into the throttle (while cruising on the HW), and the transmission in OD did go from lockup, to non-lockup and RPMs jumped about 450rpm or so.

Also, I see that some people have wired in some switch to either per lock the TC, or not allow it to go into lockup at all.

Is it possible to wire in a three way switch? One way would stop lockup entirely (assume interrupting the signal to cause it to lock up, or something), middle would allow "normal" behavior, and last way would make it always be locked up?

cruiser54

Could possibly be TPS but I'm a little doubtful at this point.

Try this. It fixed an issue on my wife's 88:

Cruiser’s Trans Plug Refreshing

Over near the trans dipstick tube are 2 rather large connectors. One is black and the other gray. These 2 connectors carry all the info between TPS, TCU, NSS, speed sensor, and trans solenoids.
Unplug each one, visually inspect for corrosion or bent pins, spray them out with electrical contact cleaner and plug them back in.
Revised 3-28-2012

jtodaro

Ok. Haven't had a chance to refresh the Trans Plug yet, but noticed something today that I forgot about a while back.

Drove about 12 miles again (about the same place I'm always driving), and it worked fine. I went into a store for 15 minutes and upon returning, it acts like it won't downshift or even go into first.

The deal was, upon driving off, I put the selector in OD (normal process), but trying to start off from a stoplight, it acted like it was indeed in OD, and wasn't doing the 1-2-3-OD thing like it normally should. I even kicked it to the floor a few times and it didn't downshift. Also tried putting it in 3, but it didn't help much, but was at least in a diff gear than OD, just still not in 1st or 2nd.

That seem like a TCU to everyone else? Also, where can I get one of these, and how much?

cruiser54

Possibly, but not probably. Clean the information superhighway of the TCU, the plugs suggested earlier. Takes less time than the post you just made.....

jtodaro

Heheh. Ok. Will do it in a little bit. Thanks.

cruiser54

Don't mean to bust your juevos, but........

I'm not 100% sure on your Jeep, but on the earlier models the TCU "shift logic" circuit grounded at the engine dipstick tube stud. How about taking the nut off there, cleaning the stud til shiny, polishing the terminal ends, and reinstalling tightly?