Spark Knock Sensor Test

NOTE: Spark Knock Sensor Test should be performed if spark knock is detected only at wide open throttle, or engine exhibits poor performance or mileage.

1) Disconnect knock sensor, check ignition timing and reset as necessary. With engine at normal operating temperature, disconnect 2-wire ignition module connector (Yellow and Black/White wires). Jumper wires together at module. See Fig 1 .

Fig 1: Spark Retard Test Connections

Courtesy of FORD MOTOR CO.

2) Check ignition timing. If timing retards 16-20 degrees, reconnect module and go to next step. If timing does not retard 16-20 degrees, replace module and repeat test.

3) With vehicle at normal operating temperature, set fast idle screw on cam step that will maintain engine speed above 1200 RPM. Read and record ignition timing.

4) Locate zone vacuum switch assembly, remove and plug vacuum supply hose. See Fig 2 . Recheck timing. If timing retards more than 5 degrees, go to step 6. If timing does not retard 5 degrees, go to next step.

5) With engine at 2400 RPM, disconnect 2-wire connector at ignition module. If timing retards, check Yellow wire for short to ground. If okay, replace MCU and retest. If timing does not retard, check Yellow wire for open circuit. If okay, replace MCU and retest.

Fig 2: Disconnecting Zone Vacuum Switch Hose

Courtesy of FORD MOTOR CO.

6) Reconnect knock sensor. Repeat ENGINE RUNNING TEST under FUNCTION TESTS, but do not simulate knock by tapping rod on intake manifold. If service code 25 is obtained, MCU system is okay. If any other code is observed, replace knock sensor and retest.