transmission downshifting to 3rd results in catastrophe

Aw-4 with 75,000 miles

Shifting from 4th down to 3rd for some highway acceleration for passing results in a bucking of the entire Jeep complete with bouncing rpm, speed, and suspension, in the driving-over-RR-tracks size of a problem. I had to play games with the shifting to get home at a reasonable speed.

Ever heard of this?

Sounds like motor/tranny mounts

From what I can tell, it isn't the transmission at all, but a power problem.

We're going with the fuel pump or filter. It's in the works right now.

It pressurizes up when I turn on accessory power, but the fact remains the Jeep is gutless and won't get above 3000 rpm unless it's in neutral.

It seems the engine just won't respond to any kind of heavy demand at any speed now. RPM's just bounce around at 3000-4000 with the pedal to the floor.

If it is an 87-90 model, a bad TPS on the TCU side will cause that problem.

But your last post sounds like a fuel problem now.

Plugged cat?

update:
Replaced Fuel pump/checked filter/etc - no difference

drove some more - finally threw some TPS codes, .... Additionally: Nothing ran correctly. It seemed it was struggling to even attain 30 mph. Shifting was just plain strange and unpredictable. Stalled in drive constantly when coasting.

Replaced TPS - no difference
Wiggled TPS plug and wires - engine rpm bounced around

electrical checks: resistance along sensor wire to the PCM reached ~1 Ohm and higher when wire was wiggled. Duh!

Replaced TPS's wiring between main harness and sensor - Success. No symptoms. Just be sure to uplug the harness before soldering, as my soldering iron itself put out some power that I didn't think to check until half-way through the job.

I also discovered the TPS sends a signal to both the PCM and the TCU (transmission control unit) directly. In the harness is a little Y-split close to the brake cylinder.

What year?

His profile say 2000.

kubtastic said:

update:


Replaced TPS - no difference
Wiggled TPS plug and wires - engine rpm bounced around

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Did you properly adjust the new TPS? that is the biggest part of replacing it is adjusting it to make sure it is sending the proper signal back to the PCM.

xj88superjeep said:

Did you properly adjust the new TPS? that is the biggest part of replacing it is adjusting it to make sure it is sending the proper signal back to the PCM.

Click to expand...

The 91-2002 TPS is not adjustable.

Ecomike said:

The 91-2002 TPS is not adjustable.

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Well damn, it sure doesn't help to tell someone to make sure he adjusted his nonadjustable TPS! LOL DOH!!! WELL, for those of you with the good ole Renix, you should make sure your TPS is adjusted properly if you are having the same trouble... UGH! sorry about that~!