Transmission won't downshift even with TCM unplugged.

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Jun 16, 2010 | 08:18 AM

JesseT

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Joined: Jun 2010

Posts: 1

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From: Hollywood, Fl

Year: 1991

Model: Cherokee

Engine: 4.0L

Transmission won't downshift even with TCM unplugged.

Hey guys, first post :\. I've been lurking around these forums for about a week as I just bought a 91 Cherokee with some... 'issues.' Got rid of my JK earlier this year which was a sad moment, but I will admit, I have grown fond of my Cherokee already! Anyways sorry for the brief introduction, I'm sure your ready to hear the problem!
When I bought the vehicle I was told that sometimes the vehicle would stay in neutral when you came to a stop.. I checked the fluid levels and saw the trannie fluid was low so I thought I had a steal. Bought the jeep for $500 and went straight to the parts store and got some trannie fluid (Checked the catalog first, glad I did, takes Merc not ATF +4.) However, on my way home I ended up being stuck in what I thought was neutral. Turned the car off for a few seconds restarted and it shifted (Could start in Drive so either NSS is gone or bypassed.) I made it home having to turn off the jeep at every light. Next day didn't have this issue. After some research I read about unhooking the TCU and since I needed to replace the starter/ignition switch, I left the lower dash with the TCU in the back of my jeep. Shifts like a champ when needed in 1 - 3 - OD. Just no downshift. This went from happening sometimes, to happening every time now. I now turn the car off as I coast to the stop light. After I turn it off, I guess whatever it is that causes it to stay in OD/whatever gear it was in when I turned it off, resets and I can put it in 1st again. I have now noticed that when it is "stuck" in high gear, I can't put it in reverse, it acts as if the TC is in free spin.

For those who don't like the long winded story here is a quick recap

-Jeep will not downshift, even with TCU unplugged.
-Jeep runs rough, rattles etc.
-Won't even go over what it acts like with the TCU plugged in
-I will test TPS today I hope.
-Fluid level is fine, will drop the pan this weekend and change anyways to test solenoids/check for metal shavings.

My question is, is there anything else I should be looking for? Maybe the something in the TC? I plan on getting a multimeter today and testing the TPS, but this wouldn't affect the shifting problem with the tcu unplugged correct? Just let me know if I missed anything to test! Thanks!