Truck Trend Garage: 1997 extended-cab Ford Ranger Torque Converter Clutch
Question: I own a 1997 extended-cab Ford Ranger with the 4.0-liter engine, 4x4, and automatic transmission. It has 136,000 miles on it. The check-engine light comes on intermittently. When the check engine light is off and I take a trip over 40 miles or so, the engine will stop going into high gear. Normally when cruising around 65 mph, the rpm are around 2000, but when this problem occurs it will stay in third gear and the rpm stay around 2500-2800. After the engine cools or is parked overnight, the transmission will drop down to 2000 rpm the next day on the way to work (10 miles away, all on the highway), and it operates just fine. But when we take a trip that's over 40 miles, it will eventually not drop into the top gear and the check engine light comes on. The light will stay on for several days, even if it does drop into high gear and work appropriately. I assume it goes through several cycles of working correctly before it goes away. I took this to my mechanic and he pulled a PO1744 code and he thought a possible PCM flash was needed, that it could be a transmission solenoid problem, or that the torque converter needed to be replaced.
Answer: I can't give you much more information than your mechanic already has. PO1744 indicates the torque converter clutch (TCC) is slipping. A lock-up torque converter clutch is controlled by a solenoid that directs hydraulic pressure to the clutch when it receives an electronic signal from the Powertrain Control Module. The clutch actually locks the engine's crankshaft to the transmission's input shaft under light-load highway conditions. When the PCM sees a difference between crankshaft speed (rpm) and transmission input shaft speed, while the clutch is commanded on, it determines the clutch is slipping and sets the appropriate trouble code. The abnormal shift conditions you're experiencing may be a symptom of the slipping clutch, or it may be the transmission going into default shift parameters when the code is set and the check engine light comes on. The diagnostic procedure begins with a reprogramming of the PCM in case there are any software updates that correct the problem. Next is testing (and possibly removing) the TCC solenoid to be sure it's activating properly and sending the correct hydraulic pressure to the clutch. If all that is okay, chances are it is the TCC itself that's slipping and the torque converter needs to be replaced.
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