scrangler Posted July 20, 2006 Share Posted July 20, 2006 I am building a 2wd for a DD and I have encountered a weird shift problem. It's an 88 4.0 AT with the power button on the dash. At 65 mph it will decide it wants to be in 2nd gear. It will downshift when you let off the throttle, then upshift back into high when you stand on the throttle. Weird! If you put it in nuetral and shut it off then turn it back on it will be fine for awhile before doing it again. Any help?? Link to comment Share on other sites More sharing options...
87manche Posted July 21, 2006 Share Posted July 21, 2006 check the TPS, if the TCU get's the wrong throttle input (like it thinks you floored it) then it will downshift. Link to comment Share on other sites More sharing options...
sinnaevd Posted July 21, 2006 Share Posted July 21, 2006 I keep getting the feeling that the TPS units are poop in the jeeps? Link to comment Share on other sites More sharing options...
87manche Posted July 21, 2006 Share Posted July 21, 2006 I keep getting the feeling that the TPS units are poop in the jeeps? If you ever replace one, crack it open, you'll see why. It's a few traces on a circuit board with some small copper fingers that ride on them. It seems a very fragile design. If any of the fingers lose tension then it doesn't work properly, get it wet and they corrode. Link to comment Share on other sites More sharing options...
Pete M Posted July 21, 2006 Share Posted July 21, 2006 Plus they are 15+ years old. Link to comment Share on other sites More sharing options...
87manche Posted July 21, 2006 Share Posted July 21, 2006 Plus they are 15+ years old. that too. Link to comment Share on other sites More sharing options...
Stumpy Posted July 21, 2006 Share Posted July 21, 2006 could a bad TPS effect the torque converter? the reason i ask is my MJ does the same thing when i and slowing down around 30-40mph and i don't think the TC is locking up at hwy speeds. also how do i check if the TC is locking up correctly? Link to comment Share on other sites More sharing options...
87manche Posted July 21, 2006 Share Posted July 21, 2006 in your case Stumpy I would say cheack the TPS, check the TV cable that goes to the trans and readjust it, and check the lockup switch on the brake pedal. It looks like another brake light switch above the , um, brake light switch. It tells the TCU when you've stepped on the brakes, and unlocks the TC. To make sure your TC is locking I would run a temporary switched 12V to th solenoid wire and lock it up manually. Just so you know it's functioning mechanically. Link to comment Share on other sites More sharing options...
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