Isuzu N-Series. Manual - part 725

6E-322    Engine Control System (4HK1) 

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.

• Inspect for a proper transmission shift pattern and down shift operation.
• Inspect the fuel quality (cetane index).
• Inspect the engine oil level and quality.
• 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.

• 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.

Checks

Action

 Engine Control System (4HK1)    6E-323

Fuel Knock / Combustion Noise

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 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: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change
with the throttle opening.

Preliminary Checks

• Diagnostic System Check – Engine Controls.
• Ensure the vehicle has an actual problem.
• Inspect for smoke associated with the combustion noise.
• Inspect the fuel quality (cetane index).
• Inspect the programmed fuel injector ID code for each cylinder.
• Inspect the Tech 2 Data List in this section.

Checks

Action

6E-324    Engine Control System (4HK1) 

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).

• 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.

• Inspect the fuel injectors. Remove the injectors and visually inspect.
• 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.

• Perform the Pre Injection Stop test with the Tech 2. Replace the injectors if engine

noise does not change when commanded Stop.

• Use the Tech 2 to observe the Cylinder Compensation for each cylinder at idle. If

there is a cylinder that is excessively high or low value, it may indicate faulty fuel
injector, weak or slightly seized cylinder or an incorrectly programmed fuel injector
ID code.

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).

• Inspect for incorrect basic engine parts such as camshaft, cylinder head, pistons,

etc.

• Inspect for any excessive oil entering combustion chamber.

Additional Checks

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

in this section.

• Inspect other possible causes that can make similar noise such as loose

component parts, bracket, mount and weak clutch damper spring.

Checks

Action

 Engine Control System (4HK1)    6E-325

Poor Fuel Economy

Checks

Action

DEFINITION: Fuel economy, as measured by actual road tests and several tanks of fuel, is noticeably lower than expected.
Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by actual road tests.

Preliminary Checks

• Remove the air cleaner and check for dirt, or for air ducts being plugged or

restricted. Replace as necessary.

• Inspect the driving habits of the owner.
• Is the A/C ON full time, defroster mode ON?
• Are the tires at the correct pressure?
• Are the tire sizes changed
• Are excessively heavy loads being carried?
• Is the acceleration too much, too often?
• Inspect for clutch slip.
• Inspect brake drag.
• Inspect dive belt tension.
• Inspect for a proper transmission shift pattern and down shift operation.
• Inspect the fuel quality (cetane index).
• Inspect the engine oil level and quality.
• Suggest to the owner to fill the fuel tank and recheck the fuel economy.
• Suggest to the driver to read the Important Facts on Fuel Economy in the Owner

Manual.

• Inspect the odometer is correctly operated.
• Inspect the programmed fuel injector ID code for each cylinder.

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.

Fuel System Checks

Inspect the fuel system for the following conditions. Refer to the Fuel System section.

• Inspect the fuel type and quality.
• Check fuel leak.

Cooling System Checks

Inspect the cooling system for the following conditions. Refer to the Cooling System
Section.

• Inspect the engine coolant level.
• Inspect the engine thermostat for always being open or for the wrong heat range.
• Inspect the engine cooling fan for always being 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.

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).