Isuzu N-Series. Service manual - part 726

6E-326    Engine Control System (4HK1) 

Excessive Smoke (Black Smoke)

Checks

Action

DEFINITION: Black smoke under load, idle or start up hot or cold.

Preliminary Check

• Ensure the vehicle has an actual problem.
• Inspect the engine control module (ECM) grounds for being clean, tight, and in their

proper locations.

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

restricted. Replace as necessary.

• Inspect the fuel quality (cetane index).
• Inspect the engine oil level and quality.
• 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.

• 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.

Fuel System Checks

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

• 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.

• 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.

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

 Engine Control System (4HK1)    6E-327

Excessive Smoke (White Smoke)

Air Intake System Checks

Inspect the air intake system for the following conditions.

• 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.

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 Check

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

Additional Checks

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

in this section.

• Inspect the excessive blow-by gasses.
• Inspect the Tech 2 Data List in this section.

Checks

Action

DEFINITION: White smoke under load, idle or start up hot or cold.

Preliminary Check

• Ensure the vehicle has an actual problem.
• Inspect the engine control module (ECM) grounds for being clean, tight, and in their

proper locations.

• Inspect the fuel quality (cetane index).
• Inspect the programmed fuel injector ID code for each cylinder.

Checks

Action

6E-328    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).

• 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

• Check for a stuck open fuel injector. Remove each glow plug from the cylinder head

and inspect the tip of the glow plugs for wet fuel. Use the cylinder compression
gauge. Proper compression is more than 1960 kPa (284 psi) and variation of each
cylinder is less than 294 kPa (43 psi). If poor compression is observed, inspect the
engine mechanical.

• 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.

• 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.

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

Air Intake System Checks

Inspect the air intake system for the following conditions.

• 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.

Checks

Action

 Engine Control System (4HK1)    6E-329

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.

• Improper valve timing
• Improper valve gap
• Broken or weak valve springs
• Worn camshaft lobes
• Inspect for any excessive fuel entering combustion chamber.
• Inspect for coolant entering the combustion chamber.

Electrical System Checks

Inspect the engine electrical for the following conditions.

• Inspect the glow plug control (preheating) system operation. Refer to Glow Control

System Check in this section.

Checks

Action