Isuzu N-Series. Manual - part 795

Engine Control System (4JH1) 6E-231

Fuel System Checks

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

• Inspect for water contamination in the fuel.
• Inspect for external fuel leaks or fuel leakage into the engine oil.
• Inspect the fuel lines between the fuel tank and fuel injection pump for tightness

and all fuel hoses for cuts, cracks and for the use of proper clamps.

Notice:
The fuel system from the fuel tank(s) to the fuel injection pump is under a slight
vacuum with the engine running. As a result, air can enter the fuel system if these
connections are not tight. Air in the fuel system will cause fuel injection pump internal
pressure fluctuations especially at high engine speed and load.

• Inspect for air in the fuel system.

Notice:
If many air bubbles appear in the fuel, check the fuel system line connections between
the fuel tank and the fuel injection pump for tightness and all fuel hoses for cuts, cracks
and for the use of proper clamps.

a. Remove the fuel hose that connects to the fuel injection pump suction side.
b. Substitute a clear hose.

Notice:
A hose must be cleaned.

c. Connect the clear hose to the fuel injection pump.
d. Bleed the fuel system.
e. Let the engine run at idle for at least 2 minutes.
f. Accelerator the engine between idle and W.O.T. (accelerator pedal full travel)

many times while observing the clear hose.

• Inspect the fuel tank vent hose for a plugged or kinked.
• Inspect inside the fuel tank for any foreign material that may be getting drawn into

the fuel line pickup causing a blocked condition. Draw fuel from the fuel tank at the
fuel line (as close to the fuel tank as possible) going to the fuel pickup tube to verify
a clean stream of fuel comes out (use the hand-held vacuum pump 5-8840-0279-0/
J-23738-A with a clear hose or equivalent). This will ensure the fuel pickup tube is
not cracked drawing air into the fuel line.

• Inspect the fuel injection pump operation.

Notice:
The fuel injection pump must be timed to the engine.

• Inspect the eye bolt for any type of restriction or collapsed gauze filter.

Notice:
If any type of restriction found, check for a condition that causes contaminated fuel,
such as the customer is using an aftermarket fuel filter or extended maintenance
interval. Also inspect fuel waxing or icing that is caused by an incorrect fuel type used
in winter season or water intrusion in the fuel system.

• 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 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.

Checks

Action

6E-232 Engine Control System (4JH1)

Lack of Power, Sluggishness, Sponginess

Additional Checks

• Inspect the generator output voltage. Repair if less than 9 volts or more than 16

volts.

• Inspect the EGR system operating correctly.
• Inspect the A/C operation.

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.

• Are the tire sizes changed?
• Are excessively heavy loads being carried?
• Inspect for clutch slip.
• Inspect brake drag.
• 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) and fuel injection pump control unit (PCU)

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

• Inspect the Tech 2 Data List in this section.
• 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 100 mg/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 parameter should change linearly from 0% to 100% according to the
accelerator pedal operation.

Checks

Action

Engine Control System (4JH1) 6E-233

Fuel System Checks

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

and all fuel hoses for cuts, cracks and for the use of proper clamps.

• Inspect for air in the fuel system.

a. Remove the fuel hose that connects to the fuel injection pump suction side.
b. Substitute a clear hose.

Notice:
A hose must be cleaned.

many times while observing the clear hose.

• Inspect the fuel tank vent hose for a plugged or kinked.
• Inspect inside the fuel tank for any foreign material that may be getting drawn into

• Inspect the fuel injection pump operation.

Notice:
The fuel injection pump must be timed to the engine.

• Inspect the eye bolt for any type of restriction or collapsed gauze filter.

• 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-234 Engine Control System (4JH1)

Hesitation, Sag, Stumble

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.

• 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 catalytic converter or 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 2100 kPa

(309 psi).

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

Additional Checks

• Inspect the generator output voltage. Repair if less than 9 volts or more than 16

volts.

• Inspect the EGR system operating correctly.
• 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.

Preliminary Checks

restricted. Replace as necessary.

• Inspect the fuel quality (cetane index).
• Inspect the engine oil level and quality.
• Inspect the Tech 2 Data List in this section.
• 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 Service Bulletins for ECM software updates.

Checks

Action

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