Isuzu KB P190. Manual - part 813

Engine Management – V6 – General Information 

Page 6C1-1–10 

 

Fuel Injection System 

Each cylinder of the V6 engine is fitted with one fuel injector. The engine control relay applies ignition positive voltage to 
the fuel injector ignition circuit. The ECM controls the operation of the fuel injectors by applying a pulse width modulated 
(PWM) ground to the fuel injector control circuit to control each fuel injector on-time. 

While the engine is running, the ECM constantly monitors the various inputs and recalculates the appropriate on-time for 
each injector. The calculation is based on the following: 

• 

The injector flow rate, 

• 

Mass of fuel passed by the energised injector per unit of time, 

• 

The desired air / fuel ratio, and 

• 

Actual air mass in each cylinder. 

The ECM calculates the duration of the fuel injector on-time to deliver the correct amount of fuel for optimum drivability 
and emission control. The period of time the fuel injector is energised is called the injector on-time and is measured in 
milliseconds (thousandths of a second). 

The V6 engine uses the sequential fuel injection system. Each fuel injector is energised individually at the correct 
moment during its firing stroke as the cylinder’s intake valves are closing to provide enough time for the fuel to atomise 
completely and mix with the intake air. 

Short Term Fuel Trim 

The short term fuel trim (STFT) represents the duration of the fuel injector on-time as calculated by the ECM, while the 
ECM is in Closed Loop mode. The STFT allows the ECM to calculate the fuel injector on-time based on the heated 
oxygen sensor (HO2S) signal input to the ECM. Therefore, the STFT is disabled when the ECM is in Open Loop mode. 

• 

If the air / fuel mixture in the exhaust is balanced (lambda = 1) or when the STFT is disabled, the STFT value is 0%. 

• 

When the HO2S sends an input signal to the ECM indicating the air / fuel mixture is rich, the STFT will be less than 
0%, which indicates the ECM is decreasing the fuel injector on-time to reduce the amount of fuel in the air / fuel 
mixture. 

• 

When the HO2S sends an input signal to the ECM indicating the air / fuel mixture is lean, the STFT will be greater 
than 0%, which indicates the ECM is increasing the fuel injector on-time to increase the amount of fuel in the air / 
fuel mixture. 

The percentage values of the STFT range from –25% to +25% and are directly proportional to the duration of the fuel 
injector on-time. 

Long Term Fuel Trim 

The ECM stores the long term fuel trim (LTFT) in its memory to adjust the fuel injector on-time according to the long term 
changes or deterioration in the engine components. The normal LTFT value is 0%. 

The following describes the LTFT operation when the engine air filter is dirty that causes a restricted intake airflow fault 
condition: 

1 

The HO2S sends an input signal to the ECM the air / fuel mixture is rich because of the reduced airflow. The STFT 
may reduce to a value of –10%, which decreases the fuel injector on-time to reduce the amount of fuel in the air / 
fuel mixture supplied to the engine. 

 

Without the use of the LTFT, the restricted airflow caused by the dirty air filter may reduce the STFT value to –10% 
until the air filter is replaced. This will decrease the range of negative adjustment available to the STFT to 
compensate for other factors. 

2 

When the ECM detects the STFT has remained at –10% for a specific period, the ECM switches to the LTFT. The 
LTFT adjusts the duration of the fuel injector on-time until the air / fuel mixture in the exhaust is balanced (lambda = 
1) and the STFT value returns to 0%. 

3 

The ECM stores this Long Term FT value in its memory, which is used to calculate the base fuel injector on-time. 

The percentage values of the Long Term FT range from –100% to +100%. If the ECM detects the LTFT values are 
outside the specified percentage range for a predetermined period, the ECM will set a Diagnostic Trouble Code and 
switch to Open Loop mode. 

Engine Management – V6 – General Information 

Page 6C1-1–11 

 

3.2 

Air / Fuel Control System 

The engine control module (ECM) controls the amount of air and fuel delivered into each of the engine cylinders. Based 
on the various ECM inputs, the ECM switches to the following air / fuel control system mode to provide the optimum air / 
fuel ratio under all engine operating conditions. 

Starting Mode 

When the ignition switch is moved to the START position and the engine begins to turn, a prime pulse may be injected to 
speed starting. As soon as the ECM receives an input signal from the camshaft position (CMP) and crankshaft position 
(CKP) sensor and determines which cylinder is in the firing stroke, the ECM applies a pulse width modulated (PWM) 
ground to the injector control circuit. The ECM monitors mass air flow, intake air temperature, engine coolant 
temperature, and throttle position to determine the required fuel injector on-time required for starting the engine. 

Run Mode 

The engine switches to run mode when the engine speed reaches 480 rpm after being started. The run mode has two 
sub-modes called Open Loop and Closed Loop.  

Open Loop Mode 

The heated oxygen sensor (HO2S) does not produce a usable signal voltage output until it reaches operating 
temperature. Therefore, while the HO2S is below its operating temperature, the ECM switches to open loop mode. 

In open loop, the ECM ignores the signals from the HO2S and calculates the required injector pulse width based 
primarily on inputs from the mass air flow (MAF), intake air temperature (IAT), and engine coolant temperature sensors. 
The system will stay in the open loop mode until the HO2S produce a usable output. 

Closed Loop Mode 

Once the HO2S reaches operating temperature and starts producing its own signal voltage output, the ECM switches to 
the closed loop mode. 

In closed loop mode, the ECM initially calculates injector pulse width based on the same sensors used in open loop, and 
additionally the ECM uses the oxygen sensor signals to modify and fine tune the fuel pulse width calculations to precisely 
maintain the ideal 14.7 to 1 air / fuel ratio. 

Acceleration Mode 

The ECM monitors and calculates input signals from the accelerator pedal position (APP) and MAF sensor signals to 
determine when the vehicle is being accelerated. If the ECM detects the accelerator pedal is depressed and there is a 
demand for the vehicle to accelerate, the ECM switches to acceleration mode. In acceleration mode, the ECM increases 
the fuel injector on-time to provide more fuel accordingly. 

Deceleration Mode 

The ECM monitors and calculates input signals from the APP and MAF sensor signals to determine when the vehicle is 
being decelerated. If the ECM detects the vehicle is decelerating, the ECM switches to deceleration mode. In 
deceleration mode, the ECM decreases the fuel injector on-time, or disables the fuel injectors for short periods, to reduce 
exhaust emissions and improve fuel economy. 

Fuel Shut-off Mode 

To protect the engine from damage or to improve the vehicle's driveability, the ECM switches to the fuel shut-off mode. In 
fuel shut-off mode, the ECM performs the following: 

• 

The ECM disables the six fuel injectors under the following conditions: 

− 

Ignition off – to prevent engine dieseling, 

− 

Ignition on but no ignition reference signal – prevents flooding or backfiring, 

− 

At high engine speed – greater than the red line (rev limiter), 

− 

At high vehicle speed – greater than the rated tire speed (vehicle speed limiter), or 

− 

Extended high speed closed throttle coast-down – reduces engine emissions and increases engine braking. 

• 

The ECM selectively disables the appropriate number of fuel injectors when torque management has been enabled. 

Engine Management – V6 – General Information 

Page 6C1-1–12 

 

Battery Voltage Correction Mode 

The ECM monitors the battery voltage circuit to ensure the voltage available to the engine management system stays 
within the specified range. A low system voltage changes the voltage across the fuel injectors, which affects the fuel 
injector flow rate. In addition, a low system voltage fault condition may cause other engine management system 
components to malfunction. 

The ECM switches to battery voltage correction mode when the ECM detects a low battery voltage fault condition. While 
in battery voltage correction mode, the ECM performs the following functions to compensate for the low system voltage: 

• 

Increases the injector on-time to maintain the correct amount of fuel being delivered, and 

• 

Increases the idle speed to increase the generator output. 

Limp Mode 

The programming in the ECM software allows the engine to run in a back-up fuel strategy or limp mode when the ECM 
fails to receive signal inputs from critical sensors or when a critical engine management fault condition exists. 

The ECM switches to limp mode to enable the vehicle to be driven until service operations can be performed. 

Engine Protection Mode 

Engine protection mode is engaged to protect engine components from friction damage in the event of an engine over-
temperature condition being detected by the ECM. 

When the ECM is in engine protection mode, fuel injectors are systematically disabled and re-activated. The injectors 
that have been shut down allow the air being drawn into the engine to assist with engine cooling. 

Clear Flood Mode 

If the engine is flooded with fuel during starting and will not start, the clear flood mode can be manually selected by 
depressing the accelerator pedal to wide open throttle (WOT). In this mode, the ECM will completely disable the fuel 
injectors, and will maintain this state during engine cranking as long as the ECM detects a WOT condition with engine 
speed less than 1,000 rpm. 

3.3 

Ignition Control System 

The electronic ignition system provides a spark to ignite the compressed air / fuel mixture at the correct time. The ECM 
maintains correct spark timing and dwell for all engine operating conditions. The ECM calculates the optimum spark 
parameters from information received from the various sensors and triggers the appropriate ignition module / coil to fire 
the spark plug. 

3.4 

Starter Motor Operation 

The engine control module controls the activation of the start relay in response to inputs from: 

• 

Ignition switch, 

• 

Battery, 

• 

Immobiliser system, and 

• 

Automatic transmission gear selector position / clutch pedal position switch for vehicles with manual transmissions. 

3.5 

Throttle Actuator Control System 

Description 

The throttle actuator control (TAC) system is used to improve emissions, fuel economy and driveability. The TAC system 
eliminates the mechanical link between the accelerator pedal and the throttle plate and eliminates the need for a cruise 
control module and idle air control motor. The TAC system comprises of: 

Engine Management – V6 – General Information 

Page 6C1-1–13 

 

• 

The accelerator pedal assembly which includes: 

− 

The accelerator pedal, 

− 

The accelerator pedal position (APP) sensor 
one, and 

− 

The accelerator pedal position (APP) sensor two.

Figure 6C1-1 – 7 

 

To avoid serious personal injury, never 
attempt to rotate the throttle plate manually 
whilst the throttle body harness connector is 
connected to the throttle body. 

• 

The throttle body assembly which includes: 

− 

the throttle position (TP) sensor one 

− 

the throttle position (TP) sensor two 

− 

the throttle actuator control (TAC) motor, and 

− 

the throttle plate. 

• 

The engine control module (ECM). 

Figure 6C1-1 – 8 

The ECM monitors the accelerator pedal position through the two APP sensors and processes this information, along 
with other system sensor inputs, to command the throttle plate to a certain position. 

The throttle plate is controlled by a direct current motor called the throttle actuator control motor. The ECM operates this 
motor in the forward or reverse direction by controlling battery voltage and / or ground to two internal drivers. The throttle 
plate is held at a rest position of seven percent open using a constant force return spring. This spring holds the throttle 
plate to the rest position when there is no current flowing to the actuator motor. 

The ECM monitors the throttle plate angle through two TP sensors. Using this information, the ECM can precisely adjust 
the throttle plate. 

The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors and the throttle 
actuator control motor circuit. It also monitors the spring return rate. These diagnostics are performed at different times 
based on whether the engine is running, not running, or whether the ECM is currently in a throttle body relearn procedure.  

Two sensors within the accelerator pedal assembly and throttle body assembly are used to provide redundancy. If a 
malfunction is detected, the throttle plate is moved to a pre-determined position. 

Every ignition cycle, the ECM performs a quick throttle return spring test to ensure the throttle plate can return to the 
seven percent rest position from the zero percent position. This is to ensure the throttle plate can be brought to the rest 
position in case of an actuator motor circuit failure.