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 Section 9 - Fuel Control
SECTION 9

SECTION 9

FUEL CONTROL

1.0 BASE PULSE WIDTH CALCULATION

The base pulse width calculation for fuel delivery is shown below:

 

BPW = BPC * MAPP * T' * A/F' * VE * F33C * BLM * DFCO * DE * CLT * F77

Where:

BPW = Base Pulse Width

BPC = Base Pulse Constant Term

MAPP = Manifold Pressure Term

T' = Inverse Temperature Term

A/F' = Inverse Air Fuel Ratio Term

VE = Volumetric Efficiency Term

F33C = Battery Voltage Correction Term

BLM = Block Learn Correction Term

DFCO = Decel Fuel Cutoff Term

DE = Decel Enleanment Term

CLT = Closed Loop Correction Term

F77 = Turbo Boost Multiplier

In the paragraphs to follow, each of the terms of the base pulse width calculation are described.

1.1 Base Pulse Constant (BPC)

The base pulse constant term serves a dual purpose. Its primary function is to provide the system the means of accounting for the displacement of the engine and the injector flow rate. The secondary function is to compensate fuel delivery for EGR

The base pulse constant is calculated as follows; based on whether or not EGR is active.

1.1.1 EGR not Desired (EGR OFF)

BPC = *F28A* (Desired EGR = 0%)

1.1.2 EGR Desired (EGR ON)

An EGR "tip-in" mode will be used to make the transition between EGR OFF and EGR ON.

1.1.2.1 EGR "Tip-In" Mode Enable

The "tip-in" mode will be enabled when the throttle position rate of change (increasing throttle) exceeds *KEGRTIND* percent per 25 mSec.

After being enabled, the "tip-in" function will become active immediately when the throttle position rate of change drops below *KEGRTIND* percent per 25 mSec.

1.1.2.2 EGR "Tip-In" Mode Function

After being enabled, the "tip-in" function will become active immediately when the throttle position rate of change drops below *KEGRTIND* percent per 25 mSec.

When EGR "tip-in" mode is active, the base pulse constant is calculated as BPC = *F28* (filtered desired EGR duty cycle) This value of base pulse constant is used until EGR 'tip-in" mode is reentered or EGR is disabled (EGR OFF).

1.1.2.2.1 Filtered Desired EGR (Duty Cycle)

The filtered desired EGR (duty cycle) is generated using a first-order software filtering technique (see General Information). The filtering coefficient is *KFILEGRD*. The filtering period is 25 mSec.

1.2 Pressure Term (MAP)

The pressure term shall be derived from the filtered value of the manifold absolute pressure transducer input (ADMAP). See General Information section 2.

1.2.1 Two-Atmosphere MAP Multiplier

The use of a two-atmosphere manifold absolute pressure (MAP) sensor is selected as follows:

*KAFOPT3* b5=0. Single atmosphere MAP sensor

*KAFOPT3* b5=1 Two-atmosphere MAP sensor

When the two-atmosphere MAP sensor is selected, the base pulse width is multiplied by a factor of two.

1.3 Temperature Term

In the speed density equation, the temperature term appears as a divisor. For purposes of software expediency, the temperature term is implemented by multiplying by a term equal to the inverse of temperature.

The inverse temperature term used in the BPW calculation is determined in the following manner:

*KAFOPT2*, b5 = I Inverse Temperature = table lookup *F31M* (Inverse Manifold Air Temperature)

*KAFOPT2*, b5 = 0 Inverse temperature = table lookup *F31C* (Inverse Coolant Temperature)

Both *F31* table values should be selected such that the respective inverse temperature value is equal to 50,000/Degrees, Kelvin.

1.4 Air Fuel Ratio Term (A/F)

The air fuel ratio term is adjusted under various conditions to meet the requirements of the engine for emissions and drivability. The following paragraphs describe the algorithms that control the value of the air fuel ratio term.

1.4.1 Crank Air Fuel Ratio

When the crank air fuel ratio is enabled on the air fuel ratio is set to a value obtained from Table *F54* as a function of coolant temperature minus the value of the time-out crank air fuel term as determined below.

1.4.1.1 Crank Air Fuel Ratio Enable

The crank air fuel ratio is applied when the ignition is ON, the run fuel mode is not enabled and the throttle position is less than *KAFCFTA*.

1.4.1.2 Crank-to-Run Air Fuel Blend

The crank-to-run air fuel blend logic provides the means to smoothly ramp from the richer crank air fuel mixture to the leaner run air fuel mixture. The crank-to-run air fuel blend logic utilizes an initial value and "target" final value.

Crank-to-Run Air Fuel Blend Initial Value

The initial value is determined at the transition between the crank fuel and run fuel modes. The value of the air fuel crank-to-run term is calculated as follows:

AFTICRT = AIRFUEL = AFCRDLTA

where: AFTICRT = Crank-to-run air fuel time-out term

AIRFUEL = Air-fuel ratio at the time run fuel mode is enabled

AFCRDLTA = *F54* (Coolant) - *KCAFTI*

1.4.1.3 Crank-to-Run Air Fuel Blend Decay Function

The blending of the air fuel ratio between crank air-fuel ratio to run air-fuel ratio Is accomplished by decaying the crank-to-run air fuel term from the following equation for air-fuel ratio.

AIRFUEL = AIRFUEL - AFTICRT

where: AIRFUEL = Air fuel ratio

AFTICRT = Crank-to-run air fuel time-out term

The time-out term is decayed as follows:

AFTICRT = AFTICRT * (*KRAFTDM*)

where: *KRAFTDM* = Crank air-fuel to run air-fuel decay multiplier

The time-out term is decayed at a rate determined by the *F64* table as a function of coolant temperature.

1.4.2 Clear Flood Air Fuel Ratio

1.4.2.1 Clear Flood Air Fuel Ratio Enable

The clear flood air fuel ratio enable is applied when the ignition is ON and either of the following sets of conditions are true.

Condition #1

1.Not in Run Fuel Mode.

2.Throttle position greater than or equal to *KAFCFTA*.

Condition #2

1.In Run Fuel Mode.

2.Engine not running.

3.Throttle position greater than or equal to *KAFCFTA*.

1.4.2.2 Clear Flood Air Fuel Ratio Function

When the clear flood air fuel ratio is enabled, the air fuel ratio is set to *KAFCF*.

1.4.3 Cold Engine Air Fuel Ratio

1.4.3.1 Cold Engine Air Fuel Ratio Enable

The cold engine air fuel ratio mode is enabled when all of the following are met:

1.Coolant temperature is less than or equal to *KAFTCTH*.

1.4.3.2 Cold Engine Air Fuel Ratio Function

The cold engine A/F ratio used depends on the TPS position. For closed throttle (CLCCMW, bit 7=1) the air fuel ratio is given by the *F57* table as a function of coolant temperature. For throttle not closed (CLCCMW, bit 7=0) the air fuel ratio is given by the *F56* table as a function of coolant temperature and manifold pressure.

1.4.3.3 Cold Engine Air Fuel Ratio Limit

A limit is placed on the cold engine air fuel ratio to improve idle quality.

1.4.3.3.1 Cold Engine Air Fuel Ratio Limit Enable

The cold engine air fuel ratio limit is enabled under the following set of conditions.

1.Cold engine air fuel ratio enabled.

2.Air fuel ratio is greater than 14.6:1.

3.Throttle is closed.

4.Vehicle speed is less than *KSTOKPH*.

1.4.3.3.2 Cold Engine Air Fuel Ratio Function

The cold engine air duel ratio is determined by one of two methods, selected by a combination of throttle position (OPEN or CLOSED) and vehicle speed.

Condition 1

1.Open throttle, or open throttle and vehicle speed greater than or equal to *KVSIDLE*.

Under this condition, cold engine air fuel ratio is derived from the *56* table, as a function of engine coolant temperature and manifold absolute pressure. A single atmosphere MAP reading or two-atmosphere MAP reading is used depending on the option selected.

Condition 2

1.Open throttle, and vehicle speed less than *KVSIDLE*. Under this condition, Cold engine air fuel ratio is derived from the *57* table, as a function of engine coolant temperature only.

1.4.3.3.3 Cold Engine Air Fuel Ratio Limit (Lean Clamp)

A limit is placed on the cold engine air fuel ratio.

1.4.3.3.4 Lean Clamp Enable

Immediately following determination of the cold engine air fuel ratio (see section 1.4.3.2), the cold engine air fuel ratio will be clamped. if the following conditions are met:

1.Cold engine air fuel ratio greater than *KMAXLEAN*, and start-up coolant temperature is less than *KAFTCLOW* or greater than or equal to *KAFTCHI*.

1.4.4 Warm Engine Air Fuel Ratio

1.4.4.1 Warm Engine Air Fuel Ratio Enable

The warm engine air fuel ratio is enabled when the following condition is met.

1.Engine coolant temperature greater than *KAFTCTH*.

1.4.4.3 Warm Engine Air Fuel Ratio Function

When the warm engine air fuel ratio is enabled, the air fuel ratio is set to *KAFSTCN*.

1.4.5 Time-out Run Air Fuel Ratio

The purpose of the time-cut run air fuel ratio function is to simulate the choke action of a conventional carburetor.

The time-out run air fuel ratio function is composed of two parts: the initial value and a decay rate. The following paragraphs describe the various aspects of time-out run air fuel ratio in detail.

1.4.5.1 Time-out Run Air Fuel Ratio Initialization

The time-out rtin air fuel ratio function is initialized when a legitimate shutdown sequence is detected prior to the last ECM reset and the system makes an engine not running to engine running transition. The time-out run air fuel ratio initialization consists of calculating new values of initial value and decay rate.

When the ECM does not detect a legitimate shutdown sequence prior to the last ECM reset, the time-out run air fuel logic calculates the value of the decay rate only. The previous value of time-out run air fuel ratio that existed at the time of the ECM reset is retained.

1.4.5.2 Time-out Run Air Fuel Ratio Initial Value

The time-out run air fuel ratio initial value is obtained from Table *F51* as function of coolant temperature.

1.4.5.3 Time-out Run Air Fuel Ratio Function

The ECM subtracts the time-cut run air fuel ratio term from the value of air fuel ratio as determined by the cold engine or warm engine logic. The value of the time-out run air fuel ratio begins as the initial value. The decay function then proceeds until the value of the time-out run air fuel ratio is reduced to zero.

1.4.5.4 Time-out Run Air Fuel Ratio Decay

The time-out run air fuel ratio decay rate is made up of two terms: the decay scale factor and the computation rate.

Engine running conditions must be met before air fuel ratio time out decay can begin.

1.4.5.4.1 Time-out Run Air Fuel Ratio Decay Calculation

The time-out run air fuel ratio decay function is accomplished by performing the calculation:

AFTIN = AFTIN-l * (*KAFDM*)

where: AFTIN = Value of the time-out run air fuel ratio term on this computation

AFTIN-l = Value of the time-air fuel ratio on the last computation

*KAFDM* = time-out run air fuel ratio decay scale factor (calibration value)

1.4.5.4.2 Time-out Run Air Fuel Ratio Decay Computation Rate

The time-out run air fuel ratio decay computation rate is obtained from the *F52* table as a function of coolant temperature.

1.4.6 Time-out Crank Air Fuel Ratio

The purpose of the time-out crank air fuel ratio function is to enrich the crank air fuel ratio during the early part of cranking. The clear flood mode will disable this function.

The time-cut crank air fuel ratio function is composed of two parts: the initial value and a decay rate. The following paragraphs describe the various aspects of time-out crank air fuel ratio in detail.

1.4.6.1 Time-out Crank Air Fuel Ratio Initialization

The time-out crank air fuel ratio function is initialized after a system reset, or the system makes an engine not cranking to engine cranking transition. The time-out crank air fuel ratio initialization consists of calculating new values of initial value and decay rate.

1.4.6.2 Time-out Crank Air Fuel Ratio Initial Value

The time-out crank air fuel ratio initial value is set to *KCAFTI*

1.4.6.3 Time-out Crank Air Fuel Ratio Function

The ECM subtracts the time-out crank air fuel ratio tern from the value of air fuel ratio when the ECM is not in the Run Fuel Mode and throttle position is less than *KAFCFTA*. The value of the time-out crank air fuel ratio begins as the initial value. The decay function then proceeds until the value of the time-out crank air fuel ratio is reduced to zero.

The time-out crank air fuel ratio is computed once each major loop or optionally at once per 2x reference pulse

*KAFOPT1*, b3 = 0 2x reference pulse air/fuel time-out

*KAFOPT1*, b3 = 1 Exponential crank air/fuel time-out

1.4.6.4 Time-out Crank Air Fuel Ratio Decay

The time-out crank air fuel ratio decay rate is made up of two terms: the decay scale factor and the computation rate.

1.4.6.4.1 Time-out Crank Air Fuel Ratio Decay Calculation

The time-out crank air fuel ratio decay function is accomplished by performing the calculation:

CAFTIN = CAFTIN-l * (*KCAFDM*)

where: CAFTIN = Value of the time-out crank air fuel ratio term on this computation

CAFTIN-l = Value of the time-out crank air fuel ratio term during previous

*KCAFDM* = Crank air fuel time out decay multiplier

1.4.6.4.2 Time-out Crank Air Fuel Ratio Decay Computation Rate

The time-out crank air fuel ratio decay computation rate is equal to *KCFTMl*. *KCFTMl* seconds must occur between each successive decay. When the computation rate is based on 2x reference pulses it is equal to *KCFTM2*. *KCFTM2* reference pulses must occur between each successive decay. (See Section 1.4.6.3)

1.4.7 Power Enrichment Air Fuel Ratio

The power enrichment function modifies the system air fuel ratio as a function of RPM and BARO to allow a "best torque" under a heavy engine load condition.

1.4.7.1 Power Enrichment Enable

Power enrichment is enabled when in the Run Fuel Mode, the engine is running in the EST mode and one of the following sets of conditions are met.

Condition #1

1.Manifold Absolute Pressure (MAP) exceeds *KPEMAPl*.

The MAP variable used depends on the engine application and sensor installed.

*KAFOPT3*, b5 = 0 Single atmosphere MAP sensor.

*KAFOPT3*, b5 = 1 Two-atmosphere MAP sensor.

Condition #2

1.Manifold Absolute Pressure (MAP) less than or equal to *KPEMAPl*, EST enabled, throttle position greater than or equal to *KPETPS*, and any of the following additional conditions:

    • Engine speed greater than or equal to *KPERPM*, or
    • Rate of change of throttle position (over 25 mSec) greater than or equal to a value from the *F63* table as a function of barometric pressure), or
    • Throttle position greater than *KPEATPS*.

Condition #3

Manifold Absolute Pressure (MAP) less than or equal to *KPEMAP1*, EST enabled, throttle position less than *KPETPS*, and any of the following additional conditions:

a.Manifold Absolute Pressure (MAP, selected according to the installed sensor, as defined above) greater than or equal to *KPEMAP2*, and engine coolant temperature greater than or equal to *KPETCTH*, or

b.Manifold Absolute Pressure (MAP, selected according to the installed sensor, as defined above) greater than or equal to *KPEMAP2*, engine coolant temperature less than *KPEMAP3*, filtered vehicle speed (MPH) less than *KPEMPH*, and engine speed greater than or equal to *KPERPM*, or

c.Manifold Absolute Pressure (MAP, selected according to the installed sensor, as defined above) greater than or equal to *KPEMAP2*, engine coolant temperature less than *KPETCTH*, MAP greater than or equal to *KPEMAP3*, filtered vehicle speed (MPH) greater than or equal to *KPEMPH*, and engine speed greater than or equal to *KPERPM1*.

Condition #4 - Forced Power Enrichment Mode.

Satisfying the criteria of this Condition will force power enrichment in the event that EST is disabled due to Malfunction Code 42 or operation in backup spark mode.

1.manifold Absolute Pressure (MAP, selected according to the installed sensor, as defined above) less than or equal to *KPEMAP1*, and,

2.EST disabled, and

3.MAP greater than *KPEMAP42*, and

4.Engine speed greater than *KPERPM42*

1.4.7.2 Power Enrichment Disable

The Power Enrichment mode will be disabled when the throttle position drops below *KPETPS* - *KTPSHYS*, and any of the following conditions are met:

1.Manifold Absolute Pressure (MAP, selected according to the installed sensor, as defined above) drops below *KPEMAP2*, or

2.Engine coolant temperature is greater than or equal to *KPETCTH*, and engine RPM drops below *KPERPM*, or

3.Engine coolant temperature is less than (*KPETCTH* -2'C) and manifold Absolute Pressure (MAP, selected according to the installed sensor, as defined above) drops below *KPEMAP3*, or

4.Engine coolant temperature is less than (*KPETCTH* -2'C) and Manifold absolute pressure (MAP, selected according to the installed sensor, as defined above) is greater than or equal to *KPEMAP3*, vehicle speed is greater than or equal to *KPEMPH*, and engine RPM drops below *KPERPM1*.

1.4.7.3 Power Enrichment Mode Function

When power enrichment is enabled, the air fuel ratio is set equal to a power enrichment air fuel ratio, which is derived from the *F61* table, as a function of engine RPM.

If vehicle speed exceeds *KPEHMPH*, and turbocharger boost mode is active, (Manifold Absolute Pressure, MAP, is greater than or equal to *KPEMAP4* (=1OOKPA)) for at least *KPEMPHTM* seconds, then the power enrichment air/fuel ratio will be reduced (air/fuel mixture made richer) by an amount *KPEAFDLT*.

The power enrichment air/fuel will continue to be reduced by *KPEAFDLT* as long as vehicle speed exceeds *KPEHMPH*. Once the reduction in air/fuel ratio is enabled, it will remain enabled until vehicle speed becomes less than or equal to *KPEHMPH*.

1.4.7.4 Power Enrichment Air Fuel Ratio Limit.

The final air fuel ratio calculated for power enrichment is compared against the current air fuel ratio. The richer of the two air fuel ratios is used.

This comparison is performed every 25 mSec when power enrichment is enabled.

1.4.8 Inverse Air Fuel Ratio (A/F')

In the speed density equation, the air fuel ratio term appears as a divisor. For purposes of software expediency the inverse air fuel ratio term is implemented by multiplying by the inverse of air fuel ratio (A/F'). The inverse air fuel ratio is derived from air fuel ratio by means of lookup Table *F32*.

1.5 Volumetric Efficiency Term (VE)

The volumetric efficiency term in the base pulse width equation is used to account for flow losses and other induction system characteristics that cause the amount of air ingested per cylinder to be less than expected under ideal (no flow loss) conditions.

The value of volumetric efficiency is calculated as the sum of two individual volumetric efficiency terms, VEl and VE2.

VE = VE1 + VEZ

1.5.1 VE1 Term

The value of the VE1 term is calculated under three conditions, based on throttle position, engine speed, and vehicle speed.

Condition 1

The VE1 term will derived from the *F29C* table (as a function of MAP and engine RPM (NTRPMX)) when:

    • throttle is not closed, or
    • throttle closed and engine RPM greater than 1600 RPM

Condition 2

The VE1 term will be derived from the *F29S* table (as a function of MAP and engine RPM (NTRPMX)) when:

    • throttle is closed, engine RPM is less than or equal to 1600 RPM, and vehicle speed is greater than *KVSIDLE*.

Condition 3

The VE1 term will be derived from the *F29S* table (as a function of MAP and engine RPM (filtered over 12.5 mSec)) when:

    • throttle is closed, engine RPM is less than or equal to 1600 RPM, and vehicle speed is less than or equal to *KVSIDLE*.

1.5.2 VE2 Term

The value of the VE2 term is derived from the *F30* table as a function of engine RPM.

1.6 Battery Voltage Correction

The purpose of the battery voltage correction term is to compensate for the variation of the fuel pump with battery voltage.

The battery voltage correction term is a multiplicative factor to the base pulse width term.

The fuel logic derives the battery voltage correction term from Table *F33* as a function of battery voltage.

1.7 Closed Loop Correction (CLT)

The closed loop correction term provides the means for the system to maintain the air fuel ratio at stoichiometry. This is accomplished by monitoring the oxygen content of the exhaust with a zirconia oxygen sensor and making adjustments to the closed loop correction term based on the oxygen sensor input. The following paragraphs describe the algorithm that is used to calculate the closed loop correction.

1.7.1 Closed Loop Mode Enable

The closed loop mode is enabled when the following criteria are met:

    • The ECM detects the oxygen sensor ready conditions. (1.7.1.1)
    • The coolant temperature criteria are met. (1.7.1.2)
    • The engine run time criteria are met. (1.7.1.3)
    • Malfunction Code 44 or 45 is not present. (See Dlagnostics)
    • HUD BPW Slew is not active. (1.7.1.4)

1.7.1.1 Oxygen Sensor Ready Test

The ECM supplies a bias voltage of approximately 450 mV through an impedance of 1MOhm to the oxygen sensor input terminals. When the oxygen sensor is cold, its internal impedance is extremely high. In this situation the voltage seen by the ECM is the bias voltage.

As the oxygen sensor warms, its internal resistance drops enabling it to overcome the bias voltage. The ECM determines the "oxygen sensor ready" state by monitoring the voltage from the oxygen sensor.

1.7.1.1.1 Oxygen Sensor Ready Criteria

The fuel control logic indicates an oxygen sensor ready *KO2AMAX* condition when the oxygen sensor Input voltage is greater than or less than *KO2AMIN*. Once the oxygen sensor ready condition is indicated, it will remain in effect until the "not ready" criteria are met or a legitimate shutdown sequence is detected.

1.7.1.1.2 Oxygen Sensor Not Ready Criteria

The oxygen sensor not ready state is indicated if the oxygen sensor input voltage does not exceed *KO2AMAX* or is not less than *KO2AMIN* for a period of time greater than *KO2ATIME*.

Once the oxygen sensor not ready condition is indicated, it will remain in effect until the oxygen sensor ready criteria are met.

If *KO2ATIME* is set equal to zero, closed loop operation will not occur.

1.7.1.1.3 Ready Test Initialization

If a legitimate shutdown sequence was detected prior to the last ECM reset, the fuel logic will initialize the oxygen sensor to the not ready state during the initialization sequence.

If a legitimate shutdown sequence was not detected prior to the last ECM reset, the fuel logic retains the oxygen sensor status that existed prior to the reset. The timers associated with the not ready test are set to zero.

1.7.1.2 Closed Loop Temperature Criterion

The coolant temperature criterion for closed loop operation is met when the coolant temperature is greater than *KCLTC*.

1.7.1.3 Time Criterion

The engine run time criterion for closed loop operation is met when one of the following conditions exist:

    • Coolant temperature at the time of the last engine not running to running transition (See EST Logic) is less than or equal to *KADSUCT* and the engine run time since the last legitimate shutdown sequence is greater than or equal to *KT2A*.

OR

    • The coolant temperature at the time of the last engine not running to engine running transition is greater than *KADSUCT* and the engine run time since the last legitimate shutdown sequence is greater than or equal to *KT1A*.

The user is reminded that in an engine stall and subsequent restart situation (ignition switch not turned off), the legitimate shutdown sequence is not detected. Additionally, in an ECM reset and subsequent re-initialization sequence, the system is initialized to the engine not running state. Both of these situations result in an engine not running to engine running transition, which will cause the fuel logic to reevaluate the engine run time requirement for closed loop operation provided it has not already expired.

Once the engine run time criteria for closed loop is met, it will remain in effect until the ECM detects a legitimate shutdown sequence.

1.7.1.4 HUD BPW SLEW Mode

If the HUD BPW SLEW is active, open loop operation is forced. If HUD BPW SLEW is not active or EGROC option has been selected closed loop will be enabled.

1.7.2 Closed Loop Correction

The closed loop correction term is derived by monitoring the value of the oxygen sensor input voltage. When the oxygen sensor indicates 3 lean air fuel ratio, the closed loop correction term is adjusted to cause a rich mixture. Conversely, when a rich air fuel ratio is indicated, the closed loop correction term is adjusted to cause a leaner mixture.

The closed loop correction term is calculated as the sum of three terms:

CORRCL = INTCLPROP-l28

where: CORRCL = closed loop correction term

INT = integrator term

CLPROP = proportional closed loop term

CLPROP is (+) if oxygen sensor indicates lean CLPROP is (-) if oxygen sensor indicates rich Each term is described below, along with the algorithm that controls this function.

1.7.2.1 Oxygen Sensor Rich/Lean Determination -

When the oxygen sensor input voltage is greater than *KCLOXTH*, a rich air fuel ratio is indicated. Conversely, if the oxygen sensor input voltage is less than or equal to *KCLOXTH*, a lean air fuel ratio is indicated.

The oxygen sensor rich/lean determination logic is performed once every 25 msec.

1.7.2.2 Closed Loop Correction Term

The closed loop correction term consists of the sum of two parts, these being the integral and proportional terms.

1.7.2.2.1 Integral Term

The operational sequence of the integrator function is as follows:

1.When the system detects an oxygen sensor transition, the fuel logic calculates a transport delay time based on engine speed (first time transition mode). The integrator does not update until this delay time is expired.

2.If the transport delay time expires without an intervening oxygen sensor transition, the integrator is updated and a new value of integrator delay is calculated based on engine speed (not first time transition mode).

3.If the new value of integrator delay expires without an oxygen sensor transition, the integrator is updated again.

4.Step 3 is repeated until an oxygen sensor transition is detected.

The above sequence continues as long as the system is operating in closed loop and the integrator reset mode is not enabled. The following paragraphs describe the various aspects of the integrator and integrator delay function in detail.

1.7.2.2.1.1 Transport Delay Time Calculation

The transport delay time is calculated as the sum of two terms.

MAP term - the MAP contribution to transport delay time is obtained from the *F23* table, as a function of MSP (Manifold Absolute Pressure).

RPM term - the RPM contribution to transport delay time is obtained from the *F24* table, as a function of engine speed.

The value of transport delay time is limited to a value less than or equal 6.375 seconds will result in the integrator never being updated.

1.7.2.2.1.2 Integrator Reset Mode Enable

The integrator reset mode is enabled when any of the following conditions are present. If none of the conditions are present, the integrator reset mode is disabled.

1.The closed loop mode is not enable (that is, system is operating in open loop fuel mode).

2.Low engine RPM reset mode enabled. The integrator will be reset when

    • engine coolant temperature greater than *KINTTCTH*.
    • filtered engine RPM drops below the desired idle speed (without air conditioning) plus *KRPMOFFL*.

The low engine RPM reset mode will remain enabled until engine RPM increases above the desired idle speed (without air conditioning) plus *KRPMOFFH*.

3.The deceleration fuel cutoff mode is enabled.

4.First time transition has occurred (see section 1.7.2.2.1.3).

5.Power enrichment mode is enabled and the integrator is less than or equal to 1.0.

6.ALDL Fuel closed loop mode is enabled, but system is not in closed loop.

7. The integrator is greater than or equal to 1.0, the oxygen sensor indicates lean, and one of the following conditions is met:

    • Not closed throttle
    • Closed throttle, vehicle speed greater than or equal to *KVSIDLE*.

When the integrator reset mode is enabled, the following action is taken:

1.The integrator is set to 1.0.

2.The integrator delay counter is set to 0.

3.The proportional correction term is set to 0.

4.The oxygen sensor variable used for the integrator slow trim logic is set to *KCLOXTH*.

1.7.2.2.1.3 First Time Transition Mode

The first time transition mode is enabled when the oxygen sensor makes a rich to lean transition or a lean to rich transition.

When the first time transition mode is enabled, the value of the integrator delay time is set equal to the transport delay time.

1.7.2.2.1.4 Not First Time Transition Mode

If the oxygen sensor has not detected a transition (rich/lean or lean/rich), the integrator delay time is derived as follows:

If engine coolant temperature is greater than or equal to *KINTDLTC*

Or

if engine coolant temperature is less than *KINTDLTC*, and open throttle, then integrator delay is derived from the *F25* table (as a function of engine speed).

Or

if engine coolant temperature is less than *KINTDLTC* and closed throttle, then integrator delay is sum of a value from the *F25* table (as a function of engine speed) and *KINTDLTA*.

1.7.2.2.1.5 Integrator Update Criteria

The integrator update calculation is performed when the integrator delay counter equals the integrator delay time. The integrator delay counter is reset when this condition is met.

1.7.2.2.1.6 Integrator Update Calculation

The integrator update calculation is performed as illustrated below:

INTN = INTN-l + STEP

where: INTN = Value of integrator for this calculation

INTN-l = Previous value of the integrator

STEP = + 1/128 for a lean condition

- 1/128 for a rich condition

1.7.2.2.1.7 Integrator Limits

When the oxygen sensor is indicating rich, the value of the integrator term is limited to a value greater than or equal to *KCLITMI*. When the oxygen sensor is indicating lean, the value of the integrator term is limited to a value less than or equal to *KCLITMX*

1.7.2.2.1.8 Integrator Slow Trim

The integrator slow trim function is enabled when the integrator reset mode is not enabled.

The slow trim logic updates the integrator at one of two different gain rates, based on the state of the throttle (open or closed).

(a) For closed throttle conditions, the following actions take place.

When the filtered value of oxygen sensor input voltage is greater than *KO2FILHC*, the integrator is decremented by 1/128. When the filtered value of oxygen sensor input voltage is less than *KO2FILLC* the integrator is incremented by 1/128.

(b) For open throttle conditions, the following actions take place.

When the filtered value of oxygen sensor input voltage is greater than a value defined by the *F67* table, as a function of MAP, the integrator is decremented by an amount determined by 1/128. When the filtered value of oxygen sensor input voltage is less than a value defined by the *F68* table, as a function of MAP, the integrator is incremented by an amount determined by 1/128.

The value of the filtered oxygen sensor is set to *KCLOXTH* when the integrator reset mode is enabled.

Slow trim logic is executed at a frequency defined by *KCNTRC* if throttle is closed, or by *KCNTRO* if throttle is open.

The integrator is limited to a maximum value of *KCLITMX* and a minimum value of *KCLITMI*.

1.7.2.2.2 Proportional Term

The proportional term is the second of the two terms that comprise the closed loop correction term. When the oxygen sensor is indicating rich, the proportional term is negative. Conversely, when the oxygen sensor is indicating lean, the proportional term is positive. The sum of the integrator and proportional terms form the closed loop correction term.

The proportional term is determined by the conditions listed below:

Prop Term = *KCLPROP* if the manifold vacuum is less than *KPROPVAC*.

    • *KPWOEGR* if the manifold vacuum is not less than *KPROPVAC* and EGR is not enabled.
    • *KPWEGR* if the manifold vacuum is not less than *KPROPVAC* and EGR is enabled.

1.7.2.2.2.1 Proportional Term Time Limit

If *KPWOEGR* is selected and the time since the last integrator update calculation exceeds *KPCDUR*, then the proportional term is set equal to zero.

1.3 Block Learn Correction

The block learn term provides the means for the system to compensate for engine to engine variation and changes in engine operating characteristics. The block learn term may be thought of as a correction or trim of the volumetric efficiency term. It is derived from the integral portion of the closed loop correction and is arranged such that corrections made by the integral term are minimized. In an ideal system, the block learn term would learn values such that the integrator never moved and the proportional term caused the oxygen sensor to change state.

1.8.1 Block Learn Correction Implementation

The block learn correction is implemented as a conditional multiplicative correction term to the base pulse width calculation.

If power enrichment is not enabled, then

BPW = BPW * BLM

where: BPW = base pulse width term

BLM = block learn multiplier

If power enrichment is enabled and the value of the block learn multiplier is greater than or equal to 1.0, then

BPW = BPW * BLM

otherwise, if the value of the block learn multiplier is less than1.0, then the base pulse width is left unchanged.

1.3.2 Block Learn Memory Cell Selection

The fuel algorithm provides two variables which will be referred to as block learn memory cells. Selection between block learn memory cells is made on the basis of open or closed throttle.

The open throttle cell is selected when the throttle sensor value is greater than the applicable threshold value. The closed throttle cell is selected when the open throttle cell is not selected.

Threshold = *KF4TPS1* if throttle is closed.

- *KF4TPS2* if throttle is open.

1.8.3 Block Learn Memory Update

The block learn memory cell values are updated by comparing the state of the integrator with the oxygen sensor indication. If the integrator was making a rich correction (increasing fuel) and the oxygen sensor indicates lean, the active block learn cell is adjusted rich. Conversely, if the integrator was making a lean correction (decreasing fuel), the active block learn cell is adjusted lean.

1.8.4 Learn Enable Criteria (Learn Control Store)

The block learn memory update calculation is performed when all of the following condition are met:

1.None of the following malfunction codes are set: Malf 21, 22, 33, 34.

2.The current coolant temperature is greater than *KLCTCLL*.

3.Air fuel ratio is equal to *KAFSTCN*.

4.For closed throttle, engine speed is less than both *KLCRPM1* and *KLCESTHU*.

5.For open throttle, manifold vacuum is not less than *KLCVACO*, altitude compensated MAP is not less than *KLCLDLO*, and engine speed is less than *KLCESTHU*.

1.8.5 Block Learn Memory Timer

Block learn memory timer shall be reset for the following conditions:

1.Closed loop integrator reset

2.The learn enable criteria are not met

3.The last block learn memory update

4.A change in block learn cell.

The block learn calculation will be made when the length of time since reset is equal to *KBLMCNT*.

1.8.6 Block Learn Memory Update Calculation

The block learn memory update calculation shown will be performed under the stated conditions.

Oxygen Block Learn

Integrator Sensor Status Update Calculation

INT GT 128 + KLCITTH Lean BLM = BLM + 1/128

INT LT 128 - KLCITTH Rich BLM = BLM - 1/123

For all other states no block learn update is performed

1.8.7 Block Learn Memory Limits

The fuel control logic will limit the value of block learn memory cells to values greater than or equal to *KBLMMIN* and less than *KBLMMAX*.

1.8.8 Block Learn Initialization

The block learn multiplier cell values are stored in nonvolatile memory and thus retained during normal power-off conditions. The block learn memory cells are initialized to a value of 1.0 (128) if any of the following conditions detected.

Condition #1

During system initialization, if the RAM error detection logic detects a nonvolatile memory failure. (See RAM Error detection and Correction.)

Condition #2

During normal system operation, if the value of the currently active block learn memory cell is greater than *KBLMMAX*.

Condition #3

During normal system operation, if the value of the currently active block learn memory cell is less than *KBLMMIN*

1.9 Decel Fuel Cutoff

The purpose of the decel fuel cutoff function is to remove fuel from the engine during deceleration conditions.

1.9.1 Decel Fuel Cutoff Enable Criteria

The decel fuel cutoff mode is enabled when all the following conditions are met:

1.Vehicle is not in Park/Neutral and IN GEAR. If malfunction code 24 is present, then the "IN GEAR" check is bypassed.

2.Altitude compensated manifold pressure less than *KDFCOMAP*, or, altitude compensated manifold pressure greater than or equal to *KDFCOMAP* and decel fuel cutoff mode enabled and altitude compensated manifold pressure less than *KDFCOMAP* +8kPa. If either malfunction code 33 or 34 are present, then the altitude compensated manifold pressure criteria is bypassed.

3.Throttle position less than *KDFCOTP*. If either malfunction code 21 or 22 is present, then the throttle position criteria is bypassed.

4.Filtered vehicle speed greater than *KDFCOSLK*. If malfunction code 24 is detected, the vehicle speed criteria is bypassed.

5.Engine RPM greater than *KDFCOSPH*. If decel fuel cutoff mode is enabled, engine RPM must remain greater than *KDFCOSPL* for decel fuel cutoff to remain enabled.

1.9.2 Decel Fuel Cutoff Stall Saver Fuel

When Decel Fuel Cutoff mode has been enabled for a long time period (in excess of *KDFCDTMR*), the manifold has essentially dried out, and no fuel exists in the induction system.

To prevent an engine stall due to fuel starvation, an amount of asynchronous fuel will be delivered under the following conditions. Decel Fuel Cutoff mode must have been enabled for an amount of time greater than *KDFCDTMR*.

1.Altitude compensated MAP increases above *KDFCOMAP* + 8kPa, or

2.Throttle position increases above *KDFCOTP*, or

3.Filtered MPH drops below *KDFCOSLK*, or

4.Transmission is in Park/Neutral or Nat in gear.

After meeting any of the above criteria, an amount of fuel equal to the product of a value from the *F58* table (as a function of elapsed time in Decel Fuel Cutoff Made) times a value from the *F75* table (as a function of engine coolant temperature) times a factor of eight.

This fuel is delivered as a synchronous AE fuel pulses.

The air fuel ratio is adjusted when exiting decel fuel cutoff mode by an amount determined by one of two conditions.

1.If the difference of the filtered RPM minus the unfiltered RPM exceeds *KDITARPM*, then the air fuel ratio is adjusted by an amount equal to the product of a value from the *F58* table (as a function of elapsed time in decel fuel cutoff mode) times a value from the *F74* table (as a function of engine coolant temperature), or

2.If the difference between the filtered RPM minus the unfiltered RPM does not exceed *KDLTARPM*, then the air fuel ratio is adjusted by an amount equal to the product of a value from the *F58* table (as a function of elapsed time in decel fuel cutoff mode) times a value from the *F73* table (as a function of engine coolant temperature).

1.9.3 Decel Fuel Cutoff Function

The decel fuel cutoff function takes the form of a multiplicative term to the base pulse width equation. When the decel fuel cutoff mode is disabled, the decel fuel cutoff term is not applied. The decel fuel cutoff mode overrides the decel enleanment mode.

When the decel fuel cutoff mode is enabled, the decel fuel cutoff term is calculated according to the equation:

DFCOSFN = DFCOSFN-1 - *KDFCOG*

where: DFCOSFN = Value of decel cutoff term at this computation

DFCOSFN-1 = Previous value of decel fuel cutoff term

*KDFCOG* = Decel fuel cutoff rate (calibration)

The above calculation is performed once each 12.5 msec. The value of the decel cutoff term is limited to a value greater than or equal to zero.

1.10 Deceleration Enleanment Term

The deceleration enleanment is a multiplicative term to the base pulse width calculation and the transient fuel accumulator (see Asynchronous Fuel.) The deceleration enleanment term is applied to the transipnt fuel accumulator once each minor loop. The user should note that this results in a "decaying action" of the transient fuel accumulator as long as deceleration enleanment is taking place. The deceleration enleanment term is calculated as described below.

1.10.1 Deceleration Enleanment Mode Enable

The deceleration enleanment mode is enabled when Power Enrichment mode is not enabled, and the current value of throttle position is less than the filter value of throttle position by a factor greater than *KDETATH*.

The power enrichment mode overrides the deceleration enleanment mode.

1.10.2 Deceleration Enleanment Delta Throttle Term

The rate of change of throttle position (decreasing) is used to calculate a delta throttle contribution tn the deceleration enleanment term.

If the rate of change of throttle position (decreasing) is greater than a threshold (defined below), the delta throttle contribution to the decel enleanment term is calculated as follows:

DETHROT = *F36*( (THRESHOLD-TPS )*8)

where: *F36* table is defined as a function of rate of change of throttle position.

TPS is the current throttle position.

THRESHOLD = Filtered throttle position if *KAFOPT3*, bit 4 = I = 12.5 mSec old throttle position if *KAFOPT3*, bit 4 = 0.

DETHROT u delta throttle contribution to decel enleanment term.

1.10.3 Deceleration Enleanment Delta MAP Term

When the current manifold pressure is greater than the filtered manifold pressure, the delta MAP term is set equal to zero.

When the current manifold pressure is less than the filtered manifold pressure by a factor greater than *KDEPMTH*, the fuel logic calculates a delta MAP deceleration enleanment as a value from Table *F35* times engine speed.

1.10.4 Deceleration Enleanment Term Calculation

The deceleration enleanment term is calculated according to the relationship:

DE = 1 - (DEMAP + DETHROT) * F34 * F39

where: DEMAP = Deceleration enleanment delta MAP term

DETHROT = Deceleration enleanment delta throttle position term

*F34 * = Value from calibration memory Table *F34 , as a function of temperature.

*F39* = DE modifier as a function of MAP or throttle position.

If the rate of change of throttle is increasing, the delta throttle contribution to the decel enleanment term is set to zero.

1.11 Turbo Boost Multiplier, *F77*

The base pulse width is compensated for turbo boost mode by a turbo boost multiplier term.

This turbo boost multiplier term is derived from the *F77* table as a function of engine RPM.

2.0 FUEL DELIVERY MODES

The fuel logic delivers fuel in three modes, synchronous, quasi -asynchronous and asynchronous.

When both synchronous and asynchronous modes are operating simultaneously, the output to the injector(s) is the logical OR of the delivery pulses delivered b-v the two modes.

2.1 Synchronous Fuel Delivery

2.1.1 Synchronous Fuel Enable Criteria

The synchronous fuel delivery mode will be enabled when ignition is ON, and any of the following conditions:

1.Engine not running, or

2.Engine running and engine RPM greater than or equal to *KQASRPMD*, or

3.Engine running, engine RPM less than *KQASRPMD*, and base pulse width greater than *KAPLH*, or if base pulse width is less than or equal to *KAPLH*, then not in quasi-asynchronous mode and base pulse width greater than *KAPLL*.

Once synchronous fuel delivery mode is enabled, it will remain enabled until base pulse width becomes less than or equal to *KAPLC*.

2.1.2 Synchronous Fuel Delivery Mode Function

When the synchronous fuel delivery mode is enabled, the fuel injector pulse width is calculated as follows:

Pulse width = BPW + INJOFFST + BPWLIN

where BPW = Base pulse width.

INJOFFST a Injector offset term.

The injector bias is a tern which compensates the delivered pulse width for the delays associated with opening and closing the injector. It is calculated as:

INJOFFST = *F92*

where the *F92* table is a function of battery voltage.

BPWLIN = Injector linearity term

The injector linearity term is calculated as:

BPWLIN = *F94*

where the *F94* table is a function of BPW (base pulse width) if BPW is less than 3.9 mSec. Otherwise, BPWLIN is set to zero.

2.2 Quasi-Asynchronous Fuel Delivery

Quasi-Asynchronous fuel delivery is used when the synchronous fuel base pulse width becomes so small that the fuel pulses cannot be accurately delivered.

Enabling quasi-asynchronous fuel mode will cause the fuel injectors to be energized every other reference pulse but for twice the duration (of the normal synchronous base pulse width). This results in the same amount of fuel being delivered, but with an accurately controllable injector pulse width.

2.2.1 Quasi-Asynchronous Fuel Enable

Quasi-Asynchronous fuel mode is enabled when the following conditions are present:

    • Ignition ON
    • Engine RUNNING
    • Engine RPM less than *KQASRPMD*.
    • Base pulse width less than or equal to *KAPLL*.

2.2.2 Quasi-Asynchronous Fuel Delivery Mode Calculation

When the quasi-asynchronous fuel delivery mode is enabled, the fuel algorithm energizes the fuel injector as follows:

Once every other reference pulse for an amount of time as follows:

EFIPWD = (BPW * 2) + BPWLIN + INJOFFST

where EFIPWO = quasi-asynchronous pulse width to be delivered by the injector.

BPW = base pulse width calculated by the fuel algorithm.

BPWLIN = base pulse width linearity term.

The injector linearity term is calculated as:

BPWLIN = *F94*

where the *F94* table is a function of BPW (base pulse width) if BPW is less than 3.9 mSec. Otherwise, BPWLIN is set to zero.

INJOFFST = Injector offset term.

The injector bias is a term which comoensates the delivered pulse width for the delays associated with opening and closing the injector. It is calculated as:

INJOFFST = *F92*

where the *F92* table is a function of battery voltage.

2.2.3 Quasi-Asynchronous to Synchronous Transition Mode.

This mode is used to make the transition from quasi-asynchronous fuel delivery to synchronous fuel delivery.

Once the base pulse width becomes larger than *KAPLH, a quasi-asynchronous to synchronous transition mode is enabled for a time period based on a multiple of 12.5 mSec.

This period is calculated as follows.

when vehicle speed is greater than or equal to *KQSYNMPH* then transition time 3 (*KREFMAXH*) * 12.5 mSec when vehicle speed is less than *KQSYNMPH* then transition time a (KREFMAXL*) * 12.5 mSec

Ouasi-Asynchronous fuel delivery will continue until the transition time elapses.

2.3 Asynchronous Fuel Delivery

Asynchronous fuel delivery mode is used to deliver fuel pulses for acceleration enrichment. These acceleration enrichment fuel pulses may be due to transient increasing engine loads such as vehicle acceleration, idle air control (IAC) transient air, and engine accessory load transients.

The fuel system provides two accumulators that contain the running sum of fuel required as a result of asynchronous base fuel and transient fuel. Each time the fuel system performs a base pulse width to asynchronous pulse width conversion, the result is added to the asynchronous base fuel accumulator. Similarly, each time the transient fuel system requires fuel delivery, the length of the required pulse is also added to the transient fuel accumulator.

2.3.1 Asynchronous Fuel Delivery Enable

When the sum of the asynchronous base fuel accumulator and the transient fuel accumulator is greater than *KAPMIN*, an asynchronous fuel pulse is delivered. If the sum of the asynchronous base and transient fuel accumulators is greater than *KAPMAX*, then a fuel pulse equal to *KAPMAX* plus INJBIAS is issued. The *KAPMAX* is subtracted from the asynchronous base fuel accumulator. If the result is less than zero, the remainder of *KAPMAX* is subtracted from the transient fuel accumulator. This process continues until the sum of the asynchronous base and transient

If the sum of the asynchronous and transient fuel accumulators is less than or equal to *KAPMAX*, a fuel pulse equal to the sum of the two accumulators plus INJBIAS (per paragraph 2.4) is issued and the two accumulators cleared. fuel accumulators is less than *KAPMIN* If the asynchronous base fuel delivery mode is disabled, the fuel logic will clear the asynchronous base fuel accumulator.

2.3.2 Acceleration Enrichment - Transient Asynchronous Fuel Term

The acceleration enrichment logic calculates and delivers additional fuel when certain engine conditions are detected. All fuel required by the acceleration enrichment logic is delivered asynchronously The acceleration enrichment fuel is composed of the sum of three terms: delta MAP, delta throttle, and IAC acceleration enrichment fuel.

2.3.2.1 Acceleration Enrichment - Delta MAP Contribution

The delta MAP logic calculates a contribution to the quantity of fuel delivery scheduled for acceleration enrichment fuel.

The delta MAP contribution will be calculated when:

1.MAP is increasing (opening throttle) at a rate in excess of *KAEPMTH*. (TWO times *KAEPMTH* tf throttle opening is greater than *KAEPMTPS*).

Otherwise the delta MAP contribution is set equal to zero. The delta MSP contribution is calculated as follows:

AEDP = *F21* (MAPN - MAPN-1).

where AEDP = delta MSP contribution to acceleration enrichment

*F21* = delta MSP term

MAPN = current MAP load value.

MAPN-1 = 12.5 mSec old MAP load value.

If the throttle opening exceeds *KAETATR*, then the final delta MAP contribution is multiplied by a factor of four, otherwise it remains as calculated above.

2.3.2.1 Acceleration Enrichment-Delta Throttle Contribution

The delta throttle logic calculates a contribution to the quantity of fuel scheduled for acceleration enrichment fuel delivery.

The delta throttle contribution will be calculated when:

1.Throttle position is increasing (opening) at a rate greater than *KAETATH*.

Otherwise, the delta throttle contribution is set equal to zero. The delta throttle contribution is calculated as follows:

AEDT = *F22* ((TFSN - TPSN-l) * 8)

where AEDT = delta TPS contribution to acceleration enrichment.

*F22* = delta throttle term

TPSN = current TPS load value.

TPSN-l = 12.5 mSec old TPS load value.

If the throttle opening exceeds *KAETATR*, then the final delta throttle contribution is multiplied by a factor of four, otherwise it remains unchanged.

2.3.2.2 Acceleration Enrichment - Increasing IAC Contribution

If the IAC logic is commanding increasing idle air, a contribution of fuel defined by *KAEISCN* is added to the quantity of fuel scheduled for acceleration enrichment fuel delivery.

If the IAC logic is commanding either no idle air change or decreasing idle air, the acceleration enrichment contribution is set to zero.

2.3.2.4 Acceleration Enrichment - Output Scaling

After each of the individual contribution terms is computed and summed, the sum term is scaled for engine temperature and engine speed compensation.

The final scaled acceleration enrichment pulse width is determined as follows:

AE = AESUM * (*F37*) * (*F38*)

where:

AESUM = Sum term of individual contributions to acceleration enrichment (delta throttle term, delta MAP term, and IAC term)

*F37* = Coolant temperature scaling table

*F38* = Engine speed scaling table

The scaled value of acceleration enrichment fuel is then summed into the asynchronous fuel accumulator.

2.4 Fuel Cutoff

Fuel delivery Is Inhibited by the presence of either of the following cutoff conditions.

2.4.1 Ignition Off Cutoff

When ignition is off (MWBG, bit 5-1), then:

(a)The ECM will not, energize the injector solenoids.

(b)The synchronous delayed TBI BPW, EFIPWD, is set to zero.

(c)The pending synchronous fuel term for accumulated fuel calculation, PENOFUEL, is set to zero.

2.4.2 High Engine Speed Cutoff

To prevent prolonged high engine speed the fuel base pulse width is set equal to zero.

2.4.2.1 High Engine Speed Enable

High engine speed fuel cutoff mode is enabled under the following conditions.:

1.Engine running (MW1, bit 7=1) and either

2.Engine speed exceeds *KFRPMHI* for time *KFRPMTIM* (if not currently in high RPM fuel shutoff Mode)

Or

3.Engine speed exceeds *KFRPMLOW* for time *KFRPMTIM* (if currently in high RPM fuel shutoff mode).

2.4.2.2 High Engine Speed Disable

High engine speed fuel cutoff mode will be disabled (fuel delivery resumed) when engine speed becomes less than or equal to *KFRPMLOW*

2.4.3 High Engine Load Fuel Shutoff

2.4.3.1 High Engine Load Fuel Shutoff Enable.

Synchronous fuel delivery will be disabled when MAP (Manifold Absolute Pressure), engine load, increases above *KWGMAPL* to all fuel delivery to be reenabled.

2.5 Accumulated Fuel Update

The fuel algorithm accounts for all fuel delivered to the engine for the purpose of computing miles per gallon.

The value of accumulated fuel is equal to the sum of all synchronous, quasi-asynchronous and acceleration enrichment fuel.

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