Don't know if I've told you this, but the engine needs to be fully warmed up before you run the codes. If not, code 21 can be logged, and you will think there is a failure.
If the car was fully warmed up, then you have a connection issue betweem the sensor and the ECM. There is only 3 places it could be. ECT connector, or the 10 Pin connector, or the 60 pin connector at the ecm.
Another way to verify that the new ECT sensor is functioning correctly is a resistance check. Get the car warm, unplug the ECT, and use a multimeter across the 2 prongs. Should get something like 2.X OHMs with a warm engine. If you search around in fordfuelinjection.com you'll find an ECT resistance table showing the resistance versus temp.
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