Electronic Spark Control (ESC) System

Electronic Spark Control Circuit:

With 4L80-E Transmission (PCM)

Electronic Spark Control Circuit:

Without 4L80-E Transmission (ECM)


Purpose:
All gas engines are equipped with electronic spark control. A knock sensor is mounted on the engine block. It is connected by a blue wire to the ESC module mounted to a bracket on top of the engine. The sensor, in response to engine knock, sends a signal to the module and from there to the ECM/PCM, located in the passenger compartment. The ECM/PCM sends a signal to the distributor to retard spark timing.

The Electronic Spark Control (ESC) system is designed to retard the spark timing up to 20° to reduce spark knock (detonation) in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

Varying octane levels in todays gasoline can cause detonation in an engine. Detonation is called spark knock.

Operation:
Electronic Control Module (ECM)
The ESC system has three components:

^ ESC Module
^ ESC Knock Sensor
^ ECM

The ESC knock sensor detects abnormal vibrations (spark knocking) in the engine. The sensor is mounted in the engine block near the cylinders. The ESC module receives the knock sensor information and sends a signal to the ECM. The ECM then adjusts the Electronic Spark Timing (EST) to reduce the spark knocking.

The ESC module sends a voltage signal (8 to 10 volts) to the ECM when no spark knocking is detected by the ESC knock sensor, and the ECM provides normal spark advance.

When the knock sensor detects spark knock, the module turns OFF the circuit to the ECM. The ECM then retards EST to reduce spark knock.

Powertrain Control Module (PCM)
If the vehicle is equipped with the 4L80-E transmission, a PCM (powertrain control module) is used instead of an ECM. The PCM performs the same and additional functions and is located in the same place as the ECM.
On a vehicle equipped with a PCM, no spark control module is used. Instead, the blue wire from the knock sensor is wired directly to the PCM.

Electronic Spark Control Knock Sensor Locations:

4.3L Engine

Knock Sensor:

All Other Gasoline Engines

Location:
Knock Sensor (KS)
The knock sensor is located in the side of the engine block.

ESC Module (with ECM only)
The ESC Module is mounted to a bracket on top of the engine.