Code 54 is the distributor pickup fuel sync signal. There are 2 connectors on the HEP, 1 is for a crank signal and the other is the fuel sync signal so the controller can locate #1 cylinder to sync the fuel injectors.
The sync signal connector is the gray one.
1985 Dodge Shelby Charger L4-135 2.2L SOHC Turbo
Vehicle Level Powertrain Management Computers and Control Systems Testing and Inspection Diagnostic Trouble Code Tests and Associated Procedures Driveability (DR) Tests DR-21A Fault Code 54-Distributor SYNC Pick-Up Circuit
DR-21A Fault Code 54-Distributor SYNC Pick-Up Circuit
Notes
With ignition switch in Off position, disconnect distributor sync pick-up electrical connector.
Place ignition switch in Run position, then connect negative lead of voltmeter to to terminal No. 3 and contact positive lead to terminal Nos. 1 and 2 of distributor sync pick-up electrical connector.
If voltmeter indicates 8 volts at both terminals, replace distributor sync pick-up.
CAUTION: Before replacing the pickup make sure the terminals in the harness connector are not spread apart so they cannot touch the sync pickup connector pins.
If voltmeter indicates no voltage at terminal No. 1, check wiring for an open circuit.
If voltmeter indicates no voltage at terminal No. 2 , proceed to Test 21 step B.
1985 Dodge Shelby Charger L4-135 2.2L SOHC Turbo
Vehicle Level Powertrain Management Computers and Control Systems Testing and Inspection Diagnostic Trouble Code Tests and Associated Procedures Driveability (DR) Tests DR-21B SYNC Pick-Up Circuit to Logic Module
DR-21B SYNC Pick-Up Circuit to Logic Module
Notes
Place ignition switch in Run position, then connect a voltmeter between terminal No. 17 of logic module blue electrical connector and ground.
If voltmeter indicates at least 8 volts, check wiring from terminal No. 17 to distributor sync pick-up for an open circuit.
If voltmeter indicates no voltage, replace logic module.