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Stoich Air Fuel Ratio (Stoich AFR)
- Stoich AFR: This value is the Stoichiometric AFR value.
This is the reference AFR used by all fuel calculations inside the
VCM. Deviations from this value are represented by divisors where
greater than one is richer and less than one is leaner. Changing
this value will effect all fuel calculations.
- Stoich AFR Table: This table is used for vehicles with
the dual fuel option (alcohol)
The base stoichiometric fuel/air rate is determined by a returned
value from this table. The position on the table is determined by
the amount of alcohol in the fuel system as reported by the
vehicles fuel composition sensor. The rate ranges from 0% to 100%
alcohol.
Afterstart Enrichment
The afterstart enrichment function provides the required enrichment
after engine cranking and then a gradual ramp (decay) into
stoichiometric fuel delivery and closed loop operation. The
afterstart enrichment adds to the current fuel/air multiplier
(equivalence ratio). If the engine enters closed loop then
afterstart enrichment is zeroed.
- Initial Adder vs. ECT: Initial adder versus engine
coolant temperature.
- Initial Adder vs. IAT: Initial adder versus inlet air
temperature.
- Decay Delay: Initial Adder is held for this long before
decay begins.
- Decay Step: Time delay between successive decays of the
afterstart enrichment value once initial delay is complete.
- Decay Mult: Multiplier applied to current afterstart
enrichment value every decay step.
- Initial Adder Soaktime Mult: Multiplier to Initial Adder
vs. ECT value based on soaktime (time between engine off and engine
restart).
- Hotsoak Enrichment: Hotsoak initial extra enrichment
adder based on ECT and soaktime (time between engine off and engine
restart).
PN/Drive Enrichment
During openloop operation, extra fuel is added during a transition
from PN to Drive for A4 transmissions.
- Initial Adder vs. ECT: Initial adder versus engine
coolant temperature.
- Decay Delay: Initial Adder is held for this long before
decay begins.
- Decay Step: Time delay between successive decays of the
PN-Drive enrichment value once initial delay is complete.
- Decay Mult: Multiplier applied to current afterstart
enrichment value every decay step.
Startup AFR Correction (V6 Engines)
Startup AFR correction is the calculation of the factor that is
subtracted from the current commanded AFR during startup/warmup. It
decays to zero depending on the decay factor and is disabled once
the engine reaches closed loop operation.
- Enable Time vs ECT: These tables control the delay
before Startup AFR Correction is enabled.
- Initial Value vs Startup ECT: This is the initial value
of the AFR correction when the engine is started. It decays to zero
based on the decay factor below.
- Decay vs Startup ECT vs. RPM: This is the decay rate of
the Initial AFR correction value. Higher numbers mean a faster
decay.
Injector Control
- Injector Offset Select: Selects either MAP or Vacuum
based injector offset table in use.
- Injector Offset vs. Battery Voltage vs. KPA Vac: This
value is added to the injector pulse width as the delay time it
takes for the injector to operate. It varies with battery voltage
and manifold vacuum.
- Injector Offset vs. Battery Voltage vs. KPA MAP: This
value is added to the injector pulse width as the delay time it
takes for the injector to operate. It varies with battery voltage
and manifold pressure.
- Injector Flow Rate vs. KPA Vac: This value is the
Injector Flow rate in g/sec. It is used to tell the VCM the size of
the injectors and also how flow rate varies with manifold vacuum
(ie. varying pressure characteristics).
- Injector Flow Rate vs. KPA MAP: This value is the
Injector Flow rate in g/sec. It is used to tell the VCM the size of
the injectors and also how flow rate varies with manifold pressure
(ie. varying pressure characteristics). On some vehicles this table
references absolute pressure drop across the injectors (hence it
includes the fuel rail pressure).
- Injector Constant: This value is used to describe the
injector flow rate in liters per gram per second. It includes a
scaling factor to account for the engine displacement. Higher
values for smaller injectors, smaller values for larger
injectors.
- Injector Pulse Width Multiplier vs. VAC: This value
multiplies the calculated injector pulse width in relation to
manifold vacuum.
- Fuel Pressure Modifier vs. Battery Voltage: This table
defines how fuel pressure varies with battery voltage.
- Skew vs. Cylinder (vehicle dependent): Many V6 and L4
calibrations allow for injector skewing to tune fueling variations
between cylinders. The skew factor is a static multiplier of the
current calculated injector pulse width for that cylinder. A value
of 1.0 provides no skew.
- Short Pulse Limit: Injector Pulses shorter than this
will be increased by the amount specified in Short Pulse
Adder.
- Short Pulse Adder: Adder to pulses shorter than Short
Pulse Limit.
- Minimum Injector PW: Minimum allowed Injector Pulse
Width (after Short Pulse adder has been added if necessary).
- Default Injector PW: Default Pulse width used when
Injector Pulse Width is less than Minimum Injector PW.
General Glow Plugs(Diesel Engines)
- Glow Plug Timer - Start: The amount of time the glow
plugs will be on when the ignition is on but the engine is not
running.
- Glow Plug Timer Start 2: The amount of time the glow
plugs will be on when the ignition is on but the engine is not
running.
- Glow Plug Timer - Run: The amount of time the glow plugs
will be on when the engine is running.
Cranking Fuel
These tables control injector priming pulses and cranking fuel
delivery.
- Cranking FA Mult Stage 1 & 2 vs. Cranking Time:
These tables are FA multipliers that determine fuel delivery in
relation to time. As cranking continues the AFR is selected from
lower rows of the table until it finally stays at the last row in
the Stage 2 table. Usually you will see a pulsing fuel pattern in
these tables.
- Cranking Leanout Factor vs. ECT vs. RPM: This table
leans out the cranking fuel based in relation to ECT and RPM. It is
a value between 0 and 1 and multiplies the Fuel/Air Mult Stage 1
& Stage 2 values.
- Prime Fuel Disable RPM: Above this RPM, 1st and 2nd
prime pulses will not be delivered.
- Soaktime - Runtime Limit: Enable Soaktimer modifiers if
last engine run time was less than this value and Soaktime ECT
condition is met.
- Soaktime ECT Threshold: Enable Soaktimer modifiers if
engine coolant temp is less than this value and Soaktime Runtime
Limit condition is met.
- Prime Re-enable Time: Prime Pulse is delivered if the
previous Prime Pulse was delivered more than this time ago.
- BARO Gain: Modifier for barometric conditions.
- Prime Runtime: Engine runtime allowed to deliver priming
pulses.
- Prime Pulse Mass: Mass of fuel delivered thru all
injectors when key is switched on and fuel pressure delay has
expired.
- First Pulse Mass: Mass of fuel delivered thru all
injectors when 1st Pulse Delay has expired and fuel pressure delay
has expired.
- First Pulse Delay: Delay before 1st Pulse Mass is
delivered.
- Second Pulse Mass: Mass of fuel delivered thru all
injectors when 1st and 2nd Pulse Delay has expired and fuel
pressure delay has expired.
- Second Pulse Delay: Delay after 1st pulse before 2nd
Pulse Mass is delivered.
- Fuel Pressure Delay: Delay after key on, before Prime
Pulse is delivered to allow for fuel pump to build pressure.
- Flood Clear Enable %TPS: If the Enable TPS value is
exceeded then fuel is cut during cranking.
- Flood Clear Disable %TPS: Fuel is resumed when the
disable TPS is reached.
Engine Over Temperature
- Engine Over Temp Fuel Mult vs. RPM: Fuel/Air multiplier
used when engine over temperature protection is enabled.