Transmission problem 2001 ranger

Installing A Torque Converter Lock Up Switch
Installing a Torque Converter lock up switch on a Ford Ranger.

The lock up TC circuit is a ground switching system. The ECU grounds the circuit to control the operation of the TC. So in order to install a switch to force lockup all you have to do is hook up a grounding circuit.

Locate pin #53 on the ECU. They are numbered on the ECU.

Tapp into the pin #53 wire in the engine management harness.

Run a wire from the pin #53 wire to a switch, then from the other side of the switch to a good ground. I ran mine to the negative battery terminal.

Note: Haynes manual says the wire is Pink and Yellow but mine is Orange. You can verify the wire color by looking at the TC plug on the transmission.

Now you can control lock up. When the switch is in the on position the lock will stay locked up regardless of engine load as long as the transmission is in 3rd or OD.

When the switch is in the off position the lock up will operated as it always did.

Note: There is no lock up in first or second. The valve body overrides it in those ranges. Also remember to turn the switch off when coming to a stop or the engine will lug down until the transmission drops out of 3rd gear.
Benefits:
You can force the TC to stay locked in 3rd and OD. When you take your foot off the gas in 3rd or OD the TC unlocks and then relocks once the gas pedal is pushed down. IMO this causes un necessary wear and heat. With this switch set up once turned on the TC will not unlock until you either turn it off or shift into 2nd gear.
 

Very detailed answer from previous responder. Sounds like a winner but more briefly there are a couple of things that could cause it if the transmission is an A4LD which is a 3 speed automatic with overdrive. There is a torque convertor lock-up solenoid inside the pan that could be faulty and A4LDs are notorius for failing or acting up due to the servos (on passenger side of transmission about midway of transmission) being exposed to heat off of the exhaust which comes so close that they put a heat shield as a patch after the first few years of A4LDs had servos baking and failing. The 2 servos can be accessed from outside the transmission and one affects two gears and the other two gears. I vaguely remember the technician at the transmission shop say that could be an issue with mine. Turned out to be the solenoid.

 I would be more inclined to believe that it is the overdrive solenoid malfunctioning. The previous writer is on the right track if you are not able to change out (after checking) the solenoid. I agree that unless you are hauling a heavy load the OD should never be disengaged which of course a driver could do by down-shifting the transmission by hand to 3rd gear. This was NOT one of Ford's "better ideas".  I have changed out the solenoid on a couple Ranger A4LDs and I had to remove the filter and the valve body briefly to remove the solenoid. My solenoid was only $30 and L lost a few quarts of transmission fluid. While I had my pan off I installed a drain plug in the transmisson pan so that I could change my fluid in the future without making a major mess. I feel the other writer was probably more of an expert but I wanted to share my experiences with Ford Ranger transmissions and I repeat my experience is limited to A4LD transmissions so count the bolts on the pan to determine what transmission you have If you do not see a tag on it.

Good luck.

Kaiser Willy

One additional thought. if the roughness you feel is caused by the torque converter chattering, this can usually be fixed by flushing the transmission and refilling it.  Don't stop with draining the pan are replacing 2 or 4 quarts of fluid. have a local transmission shop drain out as much fluid as possible and replacing the entire fluid. (somewhere about 10 to 14 quarts).  the additional cost to flush the system is worthwhile.