Troubleshooting TCM

[curtis89240SX]

How is troubleshooting of the TCM/TCU performed? I have an '89 240SX with SOHC, AT. It will only shift at around 5500 RPM. I have ran the self diagnosis on the ECM and come up with the code 55. So, I went on and unplugged the TCM and the car ran like crap, no power. I fell like the TCM is still functioning but getting a bad signal from a sensor. Perhaps the throttle postion sensor. Any ideas?

[NISTECH]

that late of a shift I doubt the TPS is responsable. you either have a malfunctioning internal trans part like the govenor or line pressure solonoid or perhaps a stuck valve in the valve body. the reason it accelerates poorly with it unpluged is it enters failsafe [3rd gear only] operation.

I am trying to recall if your car has a manual kickdown cable it seams to me it does but I am not sure. If it does there is a cable that runs to you throttle wheel from the trans. if you find there is a cable that does run from the trans to the throttle remove it from the throttle drum and try driving it with it disconnected. If the shift is now better or early that cable is out of adjustment.

[curtis89240SX]

There is no cable from the throttle to the trans. This is the second trans and it is performing exactly like the original. What tells the trans when to shift?

[NISTECH]

the TCM does and it decides when to shift based on revolution speeds both output shaft and input, the throttle request determined by TPS input. I could see if the tps was constantly giving a W/o throttle signal how it would hang so long. Disconnect the tps and drive it ,see if the extreamly late shift goes away.