Isuzu N-Series. Manual - part 724

6E-318    Engine Control System (4HK1) 

Surges / Chuggles

Exhaust System Checks

Inspect the exhaust system for a possible restriction. Refer to the Exhaust System
section.

• Inspect the exhaust brake valve for a stuck closed position.
• Inspect for a restriction in the exhaust pipes.

Engine Mechanical Checks

Inspect the engine mechanical for the following conditions. Refer to the Engine
Mechanical section.

• Inspect for poor cylinder compression. Proper compression is more than 1960 kPa

(284 psi) and variation of each cylinder is less than 294 kPa (43 psi).

• Improper valve timing
• Improper valve gap
• Broken or weak valve springs
• Worn camshaft lobes

Additional Checks

• Inspect the generator output voltage.
• Electromagnetic interference (EMI) on the reference circuit can cause an engine

miss condition. The Tech 2 can usually detect EMI by monitoring the engine speed.
A sudden increase in speed with little change in actual engine speed change
indicates that EMI is present. If a problem exists, check routing of high voltage
components, such as fuel injector solenoid wiring, near the sensor circuits.

Checks

Action

DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle seems to speed up and slow
down with no change in the accelerator pedal.

Preliminary Checks

• Diagnostic System Check – Engine Controls.
• Ensure the driver understands the A/C compressor operation.
• Use the Tech 2 in order to make sure the Vehicle Speed parameter reading

matches the vehicle speedometer.

• Inspect the engine control module (ECM) grounds for being clean, tight, and in their

proper locations.

• Inspect that the harness connectors are correctly connected.
• Inspect the fuel type and quality.
• Inspect the programmed fuel injector ID code for each cylinder.
• Inspect the Tech 2 Data List in this section.

Checks

Action

 Engine Control System (4HK1)    6E-319

Sensor Checks

Inspect the engine control sensors for the following conditions. Refer to the Tech 2
Data List in this section.

• Use the Tech 2 to observe the Fuel Rail Pressure (FRP) Sensor parameter with the

engine OFF. The FRP Sensor on the Tech 2 should read 0.9 – 1.0 volt with the key
ON and engine OFF after the engine has stopped running for a minimum of 2
minutes. If not, check for high resistance in the 5 volts reference circuit, low
reference circuit, signal circuits or for a skewed sensor.

• Use the Tech 2 to observe the Differential Fuel Rail Pressure parameter at idle and

W.O.T. (accelerator pedal full travel) in Neutral. Differential Fuel Rail Pressure
parameter should always be within 

± 5 MPa (± 725 psi).

• Use the Tech 2 to observe the Accelerator Pedal Position (APP) Angle. APP Angle

parameter should change linearly from 0% to 100% according to the accelerator
pedal operation. Also inspect the APP Angle when the accelerator pedal is steady.
If the indicating angle fluctuates, check for an intermittent open, high resistance in
the circuits or for a skewed sensor.

• Inspect the crankshaft position (CKP) sensor is tight and the flywheel

circumference is not damaged.

• Inspect the crankshaft position (CKP) sensor is tight and the flywheel teeth are not

damaged.

• Inspect the camshaft position (CMP) sensor is tight and the camshaft gear flange

surface is not damaged.

Fuel System Checks

Inspect the fuel system for the following conditions. Refer to Fuel System Check Chart
and appropriate procedure in the Fuel System section.

• Install a fuel pressure / vacuum gauge (5-8840-2844-0 / J-44638) between the fuel

filter and fuel tank to check the fuel pressure. If the fuel pressure at any engine
speed is a larger vacuum than 5 inHg, a restriction exists in the fuel supply lines
between the fuel tank and the fuel supply pump.

• Inspect the fuel supply pump operation.

Notice:
The fuel supply pump must be timed to the engine and adjustment value must be
learned to the ECM.

• Perform the Injector Balancing test with the Tech 2. Repair the wire or replace the

appropriate fuel injector that does not change engine speed when commanded
OFF.

• Perform the Injector Forced Drive test with the Tech 2. Repair the wire or replace

the appropriate fuel injector that does not create a clicking noise (solenoid
operating noise), contents an interrupted noise or has abnormal nose when
commanded ON.

Air Intake System Checks

Inspect the air intake system for the following conditions.

• Inspect the air cleaner and air intake ducts for a restriction, holes, or leaks.
• Inspect for a restriction in the turbocharger inlet duct.
• Inspect the intake throttle valve for a stuck closed position.
• Inspect for a restriction or leak in the intake manifold.

Exhaust System Checks

Inspect the exhaust system for a possible restriction. Refer to the Exhaust System
section.

• Inspect the exhaust brake valve for a stuck closed position.
• Inspect for a restriction in the exhaust pipes.

Additional Checks

• Inspect the generator output voltage.
• Inspect the EGR system operating correctly. Refer to EGR Control System Check

in this section.

• Inspect the A/C operation.

Checks

Action

6E-320    Engine Control System (4HK1) 

Lack of Power, Sluggishness, Sponginess

Checks

Action

DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the
accelerator pedal.

Preliminary Checks

• Diagnostic System Check – Engine Controls.
• Compare the vehicle with a similar unit. Ensure the vehicle has an actual problem.
• Remove the air cleaner and check for dirt, or for air ducts being plugged or

restricted. Replace as necessary.

• Have the tire sizes changed
• Are excessively heavy loads being carried?
• Inspect for clutch slip.
• Inspect brake drag.
• Inspect for a proper transmission shift pattern and down shift operation.
• Inspect the fuel quality (cetane index).
• Inspect the engine oil level and quality.
• Use the Tech 2 in order to make sure the Vehicle Speed parameter reading

matches the vehicle speedometer.

• Inspect the engine control module (ECM) grounds for being clean, tight, and in their

proper locations.

• Inspect the programmed fuel injector ID code for each cylinder.
• Inspect the Tech 2 Data List in this section.

Sensor Checks

Inspect the engine control sensors for the following conditions. Refer to the Tech 2
Data List in this section.

• Use the Tech 2 to compare the Coolant Temperature with the Intake Air

Temperature (IAT) and Fuel Temperature (FT) on a cold engine condition. If the
difference among temperature reading is more than 5

°C (9°F) on a cold engine,

check for high resistance on the low reference circuit and signal circuit or for a
skewed sensor.

• Use the Tech 2 to observe the Fuel Rail Pressure (FRP) Sensor parameter with the

engine OFF. The FRP Sensor on the Tech 2 should read 0.9 – 1.0 volt with the key
ON and engine OFF after the engine has stopped running for a minimum of 2
minutes. If not, check for high resistance in the 5 volts reference circuit, low
reference circuit, signal circuits or for a skewed sensor.

• Use the Tech 2 to observe the Differential Fuel Rail Pressure parameter at idle and

W.O.T. (accelerator pedal full travel) in Neutral. Differential Fuel Rail Pressure
parameter should always be within 

± 5 MPa (± 725 psi).

• Use the Tech 2 to observe the Boost Pressure and Barometric Pressure (BARO)

with ignition ON and engine OFF. Boost Pressure and BARO parameters should be
within the 1.0 psi (7.0 kPa) each other.

• Use the Tech 2 to observe the Accelerator Pedal Position (APP) Angle. APP Angle

parameter should change linearly from 0% to 100% according to the accelerator
pedal operation.

 Engine Control System (4HK1)    6E-321

Hesitation, Sag, Stumble

Fuel System Checks

Inspect the fuel system for the following conditions. Refer to Fuel System Check Chart
and appropriate procedure in the Fuel System section.

• Install a fuel pressure / vacuum gauge (5-8840-2844-0 / J-44638) between the fuel

filter and fuel tank to check the fuel pressure. If the fuel pressure at any engine
speed is a larger vacuum than 5 inHg, a restriction exists in the fuel supply lines
between the fuel tank and the fuel supply pump.

• Inspect the fuel supply pump operation.

Notice:
The fuel supply pump must be timed to the engine and adjustment value must be
learned to the ECM.

• Perform the Injector Balancing test with the Tech 2. Repair the wire or replace the

appropriate fuel injector that does not change engine speed when commanded
OFF.

• Perform the Injector Forced Drive test with the Tech 2. Repair the wire or replace

the appropriate fuel injector that does not create a clicking noise (solenoid
operating noise), contents an interrupted noise or has abnormal nose when
commanded ON.

Air Intake System Checks

Inspect the air intake system for the following conditions.

• Inspect the air cleaner and air intake ducts for a restriction, holes, or leaks.
• Inspect for a restriction in the turbocharger inlet duct.
• Inspect the intake throttle valve for a stuck closed position.
• Inspect for a restriction or leak in the intake manifold.
• Inspect for a worn or damaged turbocharger turbine wheel, shaft or compressor

wheel. Refer to turbocharger inspection in the Engine Mechanical section.

• Inspect for turbocharger wastegate valve operation. Refer to wastegate valve

inspection in the Engine Mechanical section.

Exhaust System Checks

Inspect the exhaust system for a possible restriction. Refer to the Exhaust System
section.

• Inspect the exhaust brake valve for a stuck closed position.
• Inspect for a restriction in the exhaust pipes.

Engine Mechanical Checks

Inspect the engine mechanical for the following conditions. Refer to the Engine
Mechanical section.

• Inspect for poor cylinder compression. Proper compression is more than 1960 kPa

(284 psi) and variation of each cylinder is less than 294 kPa (43 psi).

• Improper valve timing
• Improper valve gap
• Broken or weak valve springs
• Worn camshaft lobes

Additional Checks

• Inspect the generator output voltage.
• Inspect the EGR system operating correctly. Refer to EGR Control System Check

in this section.

• Inspect the engine overheat condition. Refer to the Engine Cooling section.
• Inspect the A/C operation.

Checks

Action

DEFINITION: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur
at any vehicle speed. The condition is usually most severe when trying to make the vehicle move from a stop. If severe enough,
the condition may cause the engine to stall.

Checks

Action