Isuzu N-Series. Manual - part 796

 Engine Control System (4JH1)    6E-235

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 parameter should change linearly from 0% to 100% according to the
accelerator pedal operation.

Checks

Action

6E-236    Engine Control System (4JH1) 

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.

Checks

Action

 Engine Control System (4JH1)    6E-237

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 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 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 Tech 2 Data List in this section.
• Inspect the Service Bulletins for ECM software updates.

Checks

Action

6E-238    Engine Control System (4JH1) 

Poor Fuel Economy

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 paramater 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.

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

circumference is not damaged.

Fuel System Checks

• If excessive smoke is present, check for an injection nozzle(s).  Remove each glow

plug from the cylinder head and inspect the tip of the glow plugs for wet by fuel.
Use the cylinder compression gauge.  Proper compression is more than 2100 kPa
(309 psi). If poor compression is observed, inspect the engine mechanical.

• 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.

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.

• Inspect for any excessive oil entering combustion chamber.

Additional Checks

• Inspect the EGR system operating correctly.
• Inspect other possible causes that can make similar noise such as loose

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

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.

Checks

Action