Isuzu N-Series. Manual - part 794

 Engine Control System (4JH1)    6E-227

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.

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.

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.

Checks

Action

6E-228    Engine Control System (4JH1) 

Cut Out, Misses

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).

• Improper mechanical timing
• Improper valve gap
• Broken or weak valve springs
• Worn camshaft lobes
• Inspect for incorrect basic engine parts.

Additional Checks

• 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 injection solenoid valve wiring, near the sensor circuits.

• Inspect for faulty engine mounts.
• Inspect faulty crank pulley.
• Inspect faulty generator & A/C compressor.
• 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: A constant jerking that follows the engine speed, usually more pronounced as the engine load increase. The
exhaust has a steady spitting sound at idle, low speed, or hard acceleration for the fuel starvation that can cause the engine to
cut-out.

Preliminary Check

• Diagnostic System Check — Engine Controls.
• Inspect that the harness connectors are correctly connected.
• 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 observe the Accelerator Pedal Position.  Accelerator Pedal

Position indicating 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

circumference is not damaged.

Checks

Action

 Engine Control System (4JH1)    6E-229

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.

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 mass air flow (MAF) sensor.

Additional Checks

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

volts.

• 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 injection solenoid wiring, near the sensor circuits.

Checks

Action

6E-230    Engine Control System (4JH1) 

Surges/Chuggles

Checks

Action

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

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 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 Mass Air Flow (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 parameter should change linearly from 0% to 100% according to the
accelerator pedal operation.  Also inspect the Accelerator Pedal Position indicating
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.