SECTION 12

ELECTRONIC SPARK CONTROL

1.0 Specification

Electronic Spark Control

2.0 Introduction

Electronic Spark is a system applied to automotive engines where undesirable fuel detonation may occur with advanced spark calculations. The ESC system provides a spark retard function when fuel detonation conditions are detected by a mechanical vibration sensitive sensor mounted on the engine.

The spark retard magnitude is proportional to a time interval of the detonation conditions. The spark retard is removed in an exponentially decaying manner so that when the detonation condition ceases, the retard is reduced to zero.

2.1 ESC/ECM System Description

The electronic spark control function is added to the electronic spark timing control by means of connecting the ESC module to the proper ECM input. The signal derived from the detonation sensor is processed by an analog signal to noise enhancement filter (SNEF). The processed signal is supplied to the ECM as an indication of the presence of detonation. The output of the SNEF shall be in a logic "low" level for the detection of detonation.

The ECM spark calculations retard spark when either the electronic spark control retard or the burst knock retard conditions are satisfied. However each function has a different calculation to determine the retard value.

3.0 Spark Retard Modes

Spark retard is calculated in either ESC retard mode or burst knock retard mode. These two modes are mutually exclusive.

3.1 ESC Retard Mode

3.1.1 ESC Retard Enable Criteria

The ESC retard function is enabled when burst knock retard is not enabled and either of the following conditions are satisfied:

1.The engine coolant temperature is greater than the value *KESCOOL* and the engine RPM is greater than or equal to *KRPMKNOB* at the same time.

2.The ALDL mode is active.

3.1.2 ESC Retard Calculation

When the ESC function is enabled, a spark retard value is added to the EST calculated spark. The ESC retard value is limited to *KRETARDM*.

The ESC Retard Value is calculated as follows:

NOCKRTDN = NOCKRTDN-1 (2 * Data PA3* A)

Where: NOCKRTDN = New Retard Value

NO CKRTDN-1 = Old Retard Value

Delta PA3 = Reference Pulse Coefficient

A = A value from F6 (RPM) table

3.1.3 ESC Retard Decay

The ESC retard value is to be decayed every 200 msec. The rate of retard decay is calculated as follows:

NOCKRTDN U NOCKRTDN-l-( NDCKRTDN-l*A)

Where: NOCKRTDN = New Retard Value NOCKRTDN~l = Old Retard Value

A = Value from F7 (RPM) table

*KESCMPEC* is substituted for value from F7 (RPM) table when manifold air pressure is less than *KESCMAP*.

3.1.4 Default Retard Application

If the ESC spark retard function is enabled and either an ESC failure has been detected (see Diagnostics) or the battery voltage is less than 9 volts, the retard value will be forced to a default value *KKRTBF*.

3.2 Burst Knock Retard Mode

3.2.1 Burst Knock Retard Enable Criteria

The burst knock retard function is enabled when all of the following criteria are satisfied:

1.The ALDL mode is not enabled.

2.The engine RPM is less than the value *KRPMKNOB*.

3.The change in throttle position within the last 12.5 msec is greater than or equal to *KBKRTPS*.

4.The engine coolant temperature is greater than the value *KESCOOL*.

3.2.2 Burst Knock Retard Disable Criteria

Once the Burst Knock function has been enabled, it will remain enabled until that time, since the function was enabled exceeds the value *KBKRTIM*, at which time it will be disabled.

3.2.3 Burst Knock Retard Calculation

When the burst knock function is enabled, a spark retard value is added to the EST calculated spark. This value is equal to *KBKRTDI*.

3.2.4 Burst Knock Retard Decay

The burst knock retard value is to be decayed only after the function has been disabled. When disabled, the retard value is decayed every 200 msec. The burst Knock Retard value is calculated as follows:

NOCKRTDN = NOCxRTDN~l~(N0CxRTD~~l*A)

Where: NOCxRTD = New Retard Value N

NOCKRTD

A N-1 = Old Retard Value

= Value from F7 (RPM) table

*KESCMPEC* is substituted for value from F7 (RPM) table when manifold air pressure is less than *KESCMAP*.

d. 0 ESC Operational Determination Logic

The Operational Determination Logic is performed every 12.5 msec to determine if Knock sensor is active. The ESC Operational flag is enabled as follows:

1.ESC operational timer is less than *KESCNOP*.

2.Delta PA3 is not equal to zero.

4.1 ESC Operational Determination Logic Disable Criteria

Once ESC Operational Determination Logic is enabled, it will remain enabled until the following conditions are met:

1.Delta PA3 equal zero.

2.Premium fuel active flag is set.

3.ESC operational timer is greater than or equal to *KESCNOP*.

5.0 Computation Rate

Retard computation is performed every minor loop (12.5 msec). Retard recovery is performed every 200 msec.