Isuzu 4HL1, Workshop Manual

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Engine Control System 1A-5
Fuel Injection Control
The fuel injection control system manages the injection
quantity, injection timing, and injection pressure
according to the status of vehicle. This system changes
the injection quantity using injector operating period,
the injection timing using injector operation timing, and
the injection pressure using SCV drive duty,
respectively. The fuel injection consists of two stages,
pilot injection and main injection, and the control
system changes the amount and timing in individual
stages according to the conditions encountered.
The ECM uses the data acquired from associated
sensors and switches to judge the current vehicle
status, i.e., startup, idling, PTO, or idle stop, and
calculate the desired injection quantity. Once the
desired injection quantity is determined, ECM
calibrates the value to determine injector energize time,
energize timing, and SCV opening and controls
injectors and the SCV accordingly.
Calculation of Desired Injection Quantity
The ECM calculates the basic injection quantity using
engine speed, accelerator pedal position, engine
coolant temperature, and other necessary parameters
and calibrates this value based on the atmospheric
pressure or the like to determine the desired injection
quantity.
Injector Control
The injector control consists of four stages: "control
stop mode" where the fuel injection is completely
stopped, "split injection mode" where two (or more)
injection shots are made for one cylinder at low engine
speeds and temperatures, "fixed injection mode" where
only main injection is made at very low engine speeds
during startup, and "normal injection mode" where the
fuel injection is made within normal engine speed
range. The proper mode is selected according to such
the parameters as engine speed, engine coolant
temperature, and DTC. The ECM uses the desired
injection quantity, intake air temperature, engine
coolant temperature, and other parameters to
determine injector energize period (desired injection
period) and injector energize timing (desired injection
timing) and control injectors according to the injection
mode selected.
SCV Control (Pump Control)
Pumps are controlled in six stages: "shutoff mode",
"start mode", "wait mode", "restart mode", "feedback
mode", and "deflate mode". The proper mode is
selected according to such the parameters as key
switch position, common rail pressure, and engine
speed. The ECM calculates desired injection pressure
and pump flow rate for the selected mode based on
intake air temperature, engine coolant temperature,
engine speed, desired injection quantity, and other
necessary parameters. Then, the ECM determines the
SCV opening (SCV drive duty) using these results and
controls the SCV.
ECM
DTC Detection Status
Battery Voltage
Key Switch Position
Engine Speed
Vehicle Speed
Engine Coolant Temp.
Status Judge
Desired Injection
Quantity
Determine
Injector
Energize Time/
Timing Determine
SCV Position
Determine
Injector
Control
SCV
Control
Intake Air Temp.
Fuel Temp.
Accelerator Pedal Position
Idle Position Switch
Clutch Switch
Neutral Switch
PTO Switch
LNW21AMF005601-X
Compensation
Compensation
Compensation
Common Rail Pressure
Idle Stop