With Speed Density Update

Electronic Spark Control Diagnosis Chart:

ESC Knock Sensor:

CIRCUIT DESCRIPTION:
The knock sensor is used to detect engine detonation, and the Electronic Control Module (ECM) will retard the electronic spark timing based on the signal being received. The circuitry, within the knock sensor, causes the ECM 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 2.5 volts. The knock sensor produces an A/C signal, which rides on the 2.5 volts DC. The amplitude and signal frequency is dependent upon the knock level.

If CKT 496 becomes open or shorted to ground, the voltage will either go above 4.8 volts, or below 0.64 volts. If either of these conditions are met for about 10 seconds, a Code 43 will be stored.

TEST DESCRIPTION:
Numbers below refer to circled numbers on the diagnostic chart.

1. This step determines if conditions for Code 43 still exist (voltage on CKT 496 above 4.8 volts or below 0.64 volt). The system is designed to retard the spark 15 degrees, if either condition exists.

2. The ECM has a 5 volt pull-up resistor, which applies 5 volts to CKT 496. The 5 volt signal should be present at the knock sensor terminal during these test conditions.

3. This step determines if the knock sensor resistance is 3900 ohms +/- 15%. If the resistance is between 3300 to 4500 ohms, the sensor is OK.

4. If CKT 496 is not open or shorted to ground and the voltage reading is below 4 volts, the most likely cause is an open circuit in the ECM. It is possible that a faulty Mem-Cal could be drawing the 5 volt signal down and it should be replaced, if a replacement ECM did not correct the problem.

DIAGNOSTIC AIDS:
Check CKT 496 for a potential open or short to ground. Also, check for proper installation of MemCal.

Refer to "Intermittents" in "Diagnosis by Symptom." - Intermittent Malfunctions