1993 F350 7.3 auto trans problem please help

[Fireman54]

I have a 1993 F350 diesel dump with auto trans. Sometimes it shifts perfect. Most of the time does not want to shift. Acts like when you go to take off it is stuck in drive and when you put it in low it shifts down to like second gear. Sometimes Overdrive works sometimes does not also sometimes when you put it in drive the torque comverter acts like it is locked up direct and it will stall the truck if you hold the brake. sometimes the transmission does nothing then it engages. I have changed the filter, had trans flushed. Help gmattson@hughes.net

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[Mark Kovalsky]

It sounds like an electrical problem. If the trans computer doesn't power up the trans will always be in fourth (overdrive) gear with the torque converter unlocked, and at maximum pressure. At idle the pump can't keep up with demand and that allows the torque converter clutch to drift on.

Locate the PCM. I think it's behind the parking brake pedal. There are red wires in pins 37 and 57 of the 60 pin connector. Check that these have +12v with the key on. The engine doesn't have to be running. If there isn't voltage there most likley the power relay that powers up the computer has failed.