have a 94 XLT with 84K mi.

Problem with Torque Converter Lockup at the wrong time.

When at operating temperature, I accelerate normally in Drive to about 35 mph. As soon as car shifts into 3rd, the torque coverter wants to locks up. This draws the RPM's down to about 1000, which is too low. This may be normal if I coast at this point, but I am still continuing with gradual acceleration. This car is now bogged down. I then push more gas and the torque coverter unlocks roughly (bangs out). It then keeps trying to lock again. This is very unpleasant for around-town driving

This also happens in Overdrive, but at higher speeds.

I had into the tranny shop for this problem about 6 mo ago. They put it on the diag machine and found no problem. They said a spark plug wire was loose and that the engine was not developing enough power. I wasn't sure I bought that because the engine seemed fine (no rough idling or loss of acceleration). Nonetheless the problem was gone and has not returned until now. I checked and "reseated" all plug wires and the problem did not go away.

Is there something I can check or even change at the "home mechanic level" before I take it in? Do these cars have an external torque converter lock solenoid that may be faulty?

I look for vacuum lines and a modulator valve, but I doubt this tranny works like my old C4 that was in my 1967 Mustang Fastback. I see there is a vacuum diaphram. Could this be a possible cause of the problem?

Any suggestions?

Thanks
Chris

 

The converter solenoid is in the valve body, just inside the pan. I would first check for a short to ground in the wire from the TCC solenoid to the PCM.