Electronic Spark Control
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
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
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
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
NOCKRTDN U NOCKRTDN-l-(
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
3.2 Burst Knock Retard Mode
3.2.1 Burst Knock Retard Enable
The burst knock retard function is
enabled when all of the following criteria are satisfied:
1.The ALDL mode is not
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
3.2.2 Burst Knock Retard Disable
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
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
d. 0 ESC Operational Determination
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
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
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.