my 94 explorer 4WD with automatic trans starting giving me problems the other day. When I drive up a hill in OD (50-60 mph), I push the pedal down (not enough to downshift, just enough to increase engine speed). Once the engine speed reaches 2600 rpm, it suddenly drops to 2200-2200 rpm. I don't feel shifting from the tranny , just the drop in engine speed. I can manually shift to D or 2nd, but the engine speed will still not get above 2600 rpm.

I ran a KOEO diagnostic - the only 2 codes I get refer to lean mixture readings from the left and right oxygen sensors (codes 172, 176). Can problems with the oxygen sensors lead to shifting problems or cause the computer to keep engine rpms low? I have replaced both oxygen sensors within the past few years and have trouble believing they are both bad. Also, I recently fixed the electric motor on the transfer case that engages 4WD hi and 4WD low. Since I had just finished working on the transfer case motor, I am wondering if I may have damaged the speed sensor (mounts to transfer case next to electric shift motor. How do you diagnose speed sensor function.

I am going to do some more diagnostics this morning - checking vacuum modulator, checking voltage and resistance of the oxygen sensors, and check the fluid level in the trans. What else can I check on?

 

Bad O2 sensor data could directly effect 3-4 shift and torque converter clutch (TCC) lockup, because those are controlled by the EEC-IV computer. You're writing as if you believe the problem is in the transmission. I could envision the symptoms you describe as the result simply of a poorly running engine with a perfectly good transmission. I would suggest that you deal with the O2 sensor codes and not worry so much about the transmission until you've resolved them.

1st thing I would do in resolving the O2 sensor codes is to run the KOER test and see if there are equivalent O2 sensor codes that come up there.