1989 Ford E-Series Van code54/4.9engine

54 air charge temperature circuit open

That description is the equivalent to unplugging the sensor. Three things can set this code. There's a break in the 5.0 volt feed wire to the sensor. The sensor is open. There's a break in the ground wire.

You already replaced the sensor so that leaves a wiring or connector problem. You should be able to back-probe the connector through the rubber seals where the wires go in. The voltage readings need to be taken with the plug connected. You should find about 0.2 volts on the ground wire and between 0.5 and 4.5 volts on the feed wire. If you find 0.0 volts on the feed wire either there's a break in that wire of your meter probe isn't making contact with the terminal. Unplug the connector, then measure on the terminal directly. With it unplugged you must find the full 5.0 volts. Even that can be misleading if there is a corroded connector terminal somewhere. Measure that voltage with the digital voltmeter AND a test light at the same time. If you still have 5.0 volts we have to look at the ground side.