Engine/Transmission (1994 - 1998) No kickdown in overdrive

[stephaner142]

Just got this truck, its a 1996 2500 auto. The problem I'm getting is the transmission wont kickdown in OD. It seems to shift fine from 1st to OD and back down when I decelerate, and it kicks down from 3rd to 2nd and 2nd to 1st. When I'm in OD end stomp on the peddle it wont downshift but if I push the OD off button it downshift. I adjusted the TV cable(it was of by 3/16") and now have tested the TPS. I'm getting 5. 14V at the censor from the PCM. At idle I'm reading . 28V and at full throttle 3. 0 volts. I'm taking ground for my voltage meter off the battery. but I'll try again tomorow and take ground off the censor to see if my voltage stays the same. I know I should be getting 1. 2V to 1. 5V at idle and at least 3. 5V at WOT.



Any suggestions, I'm stumped. thanks.

 

[HBarlow]

At what road speed are you trying to get it to downshift from OD to 3rd? The Cummins is a torque motor not a high rpm motor. It produces excellent acceleration at low rpm instead of high like a gas engine. The ECM/PCM may not be programmed to downshift at the road speed you are expecting a kickdown.

I owned an '06 with 48RE automatic but don't remember if it would downshift out of OD on driver demand. My fuzzy memory suggests it did not.

 

[stephaner142]

thats the thing, its my first diesel truck, I'm used to gassers and I thought the trannys where the same. Don't get me wrong, I opperate heavy equipement for a living. But a semi-automatic transmission on a toromont is a whole different beast. But for argument sake, I'm towing a load and I get to a hill and I accelarate, would'nt the transmission kickdown. I know a gasser would.

 

[champspa]

mine will kick down under 59 mph. and shifts up to overdrive about 43 and into lockup about 49 under light throttle

 

[Joe G.]

Depending on RPM you may not want it to kick down. The result may be just more noise and not much acceleration if RPM after kick down is way off the torque curve, especially if the governor reduces fueling.

 

[HBarlow]

If your engine rpm is at or above 1600 rpm when you want acceleration just push the pedal down. The torque curve begins at 1600 rpm but is fairly narrow on a 12 valve engine.

 

[DieselDoghouse]

What Joe G said (never met the man except here but I have ALOT of respect for him BECAUSE of here) but also - you mentioned kickdown (automatic) and cummins in the same sentence…before we go too far - have you vetted the TPS (throttle position sensor) or searched for a trouble code?? Do you still have a TPS?? Our trucks have notoriously unpredictable TPS because they're based on a transistor radio volume control (here I go…) instead of a precision instrument like an optocoupler sensor—nobody makes one!! Dirt, wear, mystical intervention at the TPS will cause the computer to shift erratically, not at all, or even prematurely (Its FUN)!! Bottom line before any transmission work - a $120 TPS (with a reasonable warranty) MAY resolve your issues. IMHO - I'm on my 4th in almost 300K