Isuzu N-Series. Service manual - part 797

 Engine Control System (4JH1)    6E-239

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?
• Have 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 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 Service Bulletins for ECM software updates.

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 Engine Coolant Temperature (ECT) 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.

Notice:
The mass air flow (MAF) sensor is heated and as a result the IAT sensor may indicate
a higher than normal intake air temperature if the ignition switch is being ON. FT
sensor is internal to the PCU and it is part of the fuel injection pump assembly.

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 or leak in the intercooler.
• Inspect for a restriction in the turbocharger inlet duct.
• Inspect for a restriction or deposit in the intake throttle bore.
• Inspect for a restriction or leak in the intake manifold.
• Inspect for a restriction or damage at MAF sensor.

Exhaust System Checks

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

• Inspect for a restriction in the catalytic converter or 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 2100 kPa

(309 psi).

Checks

Action

6E-240    Engine Control System (4JH1) 

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) and fuel injection pump control unit (PCU)

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 Service Bulletins for ECM software updates.

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 Engine Coolant Temperature (ECT) 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.

Notice:
The mass air flow (MAF) sensor is heated and as a result the IAT sensor may indicate
a higher than normal intake air temperature if the ignition switch is being ON. FT
sensor is internal to the PCU and it is part of the fuel injection pump assembly.

• Use the Tech 2 to compare the MAF Sensor parameter with the Desired MAF

parameter. Start the engine and warm up (allow engine coolant temperature to
reach at least 60

°C [140°F] ).  The MAF Sensor parameter must follow the Desired

MAF parameter within 100mg/strk.  If not, inspect the air intake system, EGR
system components and contaminated, skewed or slow MAF sensor

• Use the Tech 2 to observe the Accelerator Pedal Position. Accelerator Pedal

Position indicating 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 injection nozzle(s) for proper splay condition or operating pressure.

Notice:
Only first stage of operating pressure can be checked.

• Inspect the timing device operating correctly. Observe the Actual Injection Timing

parameter with the Tech 2 while running the engine. The Actual Injection Timing
parameter must follow the Desired Injection Timing within 2

°CA on each engine

speed. Engine idle > around 2000 RPM > around 3000 RPM. If not, inspect the fuel
system restriction, air in the fuel or fuel injection pump operation.

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 or leak in the intercooler.
• Inspect for a restriction in the turbocharger inlet duct.
• Inspect for a restriction or deposit in the intake throttle bore.
• Inspect for a restriction or leak in the intake manifold.
• Inspect for a restriction or damage at MAF sensor.
• 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 for a restriction in the catalytic converter or exhaust pipes.

 Engine Control System (4JH1)    6E-241

Excessive Smoke (White Smoke)

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 2100 kPa

(309 psi).

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

etc.

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

Additional Checks

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

Checks

Action

DIFINITION: 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) and fuel injection pump control unit (PCU)

grounds for being clean, tight, and in their proper locations.

• Inspect the fuel quality (cetane index).
• Inspect the Service Bulletins for ECM software updates.

Sensor Check

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 Engine Coolant Temperature (ECT) 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.

Notice:
The mass air flow (MAF) sensor is heated and as a result the IAT sensor may indicate
a higher than normal intake air temperature if the ignition switch is being ON. FT
sensor is internal to the PCU and it is part of the fuel injection pump assembly.

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

circumference is not damaged.

Fuel System Checks

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

• Inspect the fuel injection nozzle(s) for proper splay condition or operating pressure.

Notice:
Only first stage of operating pressure can be checked.

• Inspect the timing device operating correctly. Observe the Actual Injection Timing

parameter with the Tech 2 while running the engine. The Actual Injection Timing
parameter must follow the Desired Injection Timing within 2

°CA on each engine

speed. Engine idle > around 2000 RPM > around 3000 RPM. If not, inspect the fuel
system restriction, air in the fuel or fuel injection pump operation.

Checks

Action

6E-242    Engine Control System (4JH1) 

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 or leak in the intercooler.
• Inspect for a restriction in the turbocharger inlet duct.
• Inspect for a restriction or leak in the intake manifold.
• Inspect for a restriction or damage at MAF sensor.
• Inspect for a worn or damaged turbocharger turbine wheel, shaft or compressor

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

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 2100 kPa

(309 psi).

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

etc.

• Improper mechanical 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.  Refer to the Engine Electrical
section.

• Inspect the glow plug control (preheating) system operation.

Checks

Action