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IGNITION TRIMS Tab
IGNITION TRIMS Tables
IAT IGNITION TRIM
- IAT IGNITION TRIM - This table contains ignition trims based on
DENSITY CORRECTED IAT that are applied when the
throttle is open. Positive values are advance, negative values are retard.
ECT IGNITION TRIM
- ECT IGNITION TRIM - This table contains ignition trims based on ECT that are applied when
the throttle is open.
Positive values are advance, negative values are retard.
ECT IDLE IGNITION TRIM
- ECT IDLE IGNITION TRIM - This table contains ignition trims based on ECT that are applied when
the throttle is closed. Positive values are advance, negative values are retard.
See also Throttle Closed Ignition Timing Table.
Advanced Ignition Parameters
These parameters are used to set the minimum and maximum timing deltas and absolute limits.
(TPSITA is "TPS Ignition Timing Adjustment", or ignition trim due to throttle movement.
See ACCEL IGNITION TRIM Parameters
below for TPSITA details.)
- MAX IGN RETARD DELTA (normal) - This is the maximum number of degrees that the ignition timing
is allowed to be retarded per engine cycle. This smooths large ignition retard changes under normal
- MAX IGN RETARD DELTA (TPSITA) - This is the maximum number of degrees that the ignition timing
is allowed to be retarded per engine cycle when TPSITA ia active. This allows larger ignition
retard changes when TPSITA is active.
- MAX IGN ADVANCE DELTA - This is the maximum number of degrees that the ignition timing
is allowed to be advanced per engine cycle. This smooths large ignition advance changes under normal
- MAX IGN ADVANCE - This sets the maximum ignition advance timing
before any knock timing adjustment.
- IGN RETARD MAX - This sets the maximum ignition retard timing
before any knock timing adjustment.
- INITIAL TIMING BTDC - This sets the initial ignition timing and is what should be displayed
for Final IGN on the "Data Screen" with igntion on, engine not running.
[-] COIL DWELL
DWELL BATTERY VOLTAGE FACTOR Table
- DWELL BATTERY VOLTAGE FACTOR - This table contains factors, based on battery voltage,
that are multiplied by dwell to adjust for fluctuations in battery voltage.
DWELL @12V Table
- DWELL @12V - This table contains dwell, or coil charge time, values based on RPM. Values
are at a battery voltage of 12.0V, which corresponds to a DWELL BATTERY VOLTAGE FACTOR of 1.00.
Knock System Description
The knock system has 2 parts: Knock Detection
and Knock Analysis
Knock detection is performed during the power stroke for each cylinder.
The ECU maintains a weighted average knock voltage for each cylinder.
These cylinder voltages are initialized to 2.56V and
the weighted average knock voltage for each cylinder is controlled by VOLTAGE SENSITIVITY
If the current knock voltage is greater than the average knock voltage for the current cylinder plus
the CYLINDER KNOCK VOLTAGE LIMIT
for that cylinder at the curent RPM, the Knock Count is incremented, otherwise the
weighted average knock voltage for that cylinder is updated.
Basically the ECU maintains a weighted average noise level (average knock voltage) for each cylinder,
and when the noise from a cylinder goes above this level plus the "knock noise limit",
knock is detected and the Knock Count is incremented.
If Enable Knock Analysis
is set, knock analysis is performed every 10msec.
While the engine is operating within the knock analysis zone specified by
knock_zone_min_load and knock_zone_max_rpm, and the throttle is open, the ECU maintains a
The knock_adjustment is increased (advance) or decreased (retard) based on the following:
Every 100 msecs, knock_adjust_advance is added to knock_adjustment
If Knock Count is greater than 0, knock_adjust_retard is subtracted from knock_adjustment
If knock_adjustment indicates retarded timing, Knock Trim is then set based on knock_adjustment.
If engine operation takes it outside the knock analysis zone, and the throttle is still open,
Knock Trim is set to the average knock_adjustment while operating in the knock analysis zone.
Finally Knock Trim is checked against the previous adjustment to keep the maximum delta
below MAX RETARD DELTA. It is then compared and limited to the knock retard limit from the
KNOCK RETARD LIMIT table.
Note that Knock Trim is applied AFTER the IGN RETARD MAX
limit is checked!
- Enable Knock Sensor - Enables knock sensor diagnostics only. Knock detection still
functions if this is disabled.
- Enable Knock Analysis - Enables knock analysis. If disabled, Knock Count is
still set, provided a knock sensor is connected.
- VOLTAGE SENSITIVITY - This determines the weighted average knock voltage for each cylinder
and is the percentage of the current knock voltage that is applied to the average knock voltage for
the current cylinder.
- MAX RETARD DELTA - This limits the number of degrees the ignition can be retarded per stroke.
- INVALID RETARD - If the knock sensor fails diagnostics, the ignition timing is retarded
this number of degrees as a safety measure.
ANALYSIS ZONE PARAMETERS
These parameters specify the limits of the lower right (high load, low RPM) quadrant of the
timing map, or knock analysis zone, where knock analysis is performed.
- MAX RPM - Sets knock_zone_max_rpm.
- MIN MAP LOAD - Sets knock_zone_min_load when current load source is MAP.
- MIN MAF LOAD - Sets knock_zone_min_load when current load source is MAF.
- RETARD FACTOR - This factor is multiplied by the Knock Count to set knock_adjust_retard and
controls how much the timing is retarded when a knock event occurs (Knock Count_ > 0).
Increase to increase knock timing retard.
- ADVANCE FACTOR - Sets knock_adjust_advance. This value controls the duration of retarded
timing for a knock event (timing retarded due to knock). Increase to decrease knock retard duration.
CYL VOLT LIMITS
CYLINDER KNOCK VOLTAGE LIMIT Tables
These table contain the stock knock voltage limits for each cylinder, based on RPM.
Looking at the values in these tables, the levels for cylinder 3 are higher than those for cylinder 2,
which are higher than those for cylinders 4 and 1. This is due to the physical location of the
knock sensor on the block and the acoustic signature of each cylinder relative to the knock sensor
location. Where the table values are 5.10V, knock detection is effectively disabled because the
knock voltage can never be above 5.0V.
- CYLINDER KNOCK VOLTAGE LIMIT - If the Knock Count at a certain RPM is too sensitive,
increase that limit. With another means of knock detection, these tables can be tuned for more
precise knock detection.
KNOCK RETARD LIMIT Table
- LOAD SOURCE - Select the active load source when knock analysis is active (engine
operating in knock zone of timing map).
- KNOCK RETARD LIMITS - Sets the maximum ignition knock retard based on RPM and load. The
load and RPM scales can be edited.
[-] ACCEL IGNITION TRIM
Accel Ignition Trim, also called "TPS Ignition Timing Adjustment" (TPSITA), provides initial
throttle opening, or "tip-in" retard, which in the old carburetor days, was called "vacuum advance".
TPSITA occurs in 2 phases. The first phase is called "Tip-In Retard" and is based on TPS opening rate
of change (dTPS). This reduces spark knock at throttle tip-in.
The second phase is called "Tip-In dRPM Ignition Trim" and is based on RPM rate of
change (dRPM). This helps maitain engine power while the RPM is fluctuating as the clutch is engaged.
There are a number of criteria that must be met to activate the "Tip-In Retard" phase.
If ECT is at least MIN ECT, and vehicle speed is below MAX SPEED, and
engine load is below either MAX MAF LOAD or MAX MAP LOAD
(depending on the current load source), and the change in TPS percent is at least dTPS DEADBAND,
and rpm is above MIN RPM, and no more than MAX RPM, and
gear is below or equal MAX GEAR, the "Tip-In Retard" phase is initiated. This
initializes the tpsita_decay_factor to its maximum value and starts the tpsita_timer.
If the transmission is shifted above MAX GEAR, TPSITA is canceled.
Tip-In Retard Phase
During this phase, TPS Trim
= tpsita_retard x tpsita_decay_factor. (tpsita_retard is set from the
TPSITA dTPS Retard Table
) If at any point, the newly calculated tpsita_retard value
is greater than the previous value, it is used, thereby maximizing the amount of retard based on rate of
throttle opening. Every 10msec, DECAY DECREMENT
is subtracted from the tpsita_decay_factor
which decays the value of TPS Trim
. When tpsita_timer = dTPS Time
the "Tip-In dRPM Ignition Trim" phase begins.
TPSITA dTPS Retard Table
Sets the initial value of tpsita_retard based on the rate of throttle opening, or dTPS.
Tip-In dRPM Ignition Trim Phase
During this phase, the change in rpm per engine cycle (180º) is evaluated every 10msec. As long as the
RPM is increasing or steady, TPS Trim
continues to decay to 0. If at any point the RPM drops,
from that point on, TPS Trim
is set based on the rpm difference and wheather it is falling,
rising, or steady:
TPS Trim = RPM FALLING ADVANCE * dRPM/50
RPM Falling and tpsita_decay_factor = 0:
TPS Trim = RPM FALLING DECAY * dRPM/50
TPS Trim = RPM RISING RETARD * dRPM/50
This phase continues until tpsita_timer = DURATION TIMER, at which point TPS Trim is
reset to 0.
The calculated value of TPS Trim
is kept between MAX ADVANCE
and MAX RETARD
[-] CYLINDER TRIMS
CYLINDER IGNITION TRIM Tables
These tables provide individual cylinder ignition timing trim capability.
- CYLINDER 1 IGNITION TRIM - Contains ignition timing trims (positive are advance, negative
are retard) for each cylinder based on RPM.
- All other cylinder tables function the same. - .
CRANKING IGNITION Table
This table contains ignition timing values used while in cranking mode.
(See also Cranking Mode Definition
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- CRANKING IGNITION - Ignition timing BTDC based on ECT used while in cranking mode.
If cranking RPM is below 100rpm, the timing is retarded by multiplying by rpm/100.
Copyright © 2013 David F. Dunn, TunerCode