Isuzu KB P190. Manual - part 488

ENGINE CONTROL SYSTEM (4JK1/4JJ1)   6E-335

Air Intake System Checks

Inspect the air intake system for the following conditions.

• Air cleaner, air intake ducts and charge air cooler for a restriction, holes, or leaks.

• A restriction in the turbocharger inlet duct.

• Intake throttle valve for a stuck condition.

• A restriction or leak in the intake manifold.

• A restriction or damaged at MAF sensor.

• Perform the Swirl Control Solenoid Test with a scan tool. Inspect the diaphragm

valve operation when it commanded ON/ OFF.

• Turbocharger wastegate valve operation. Refer to wastegate valve inspection in the

Engine Mechanical section. (Standard output)

• Turbocharger nozzle control actuator operation. Refer to Turbocharger Control

System Check in this section. (High output)

Exhaust System Checks

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

Additional Checks

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

this section.

• Inspect the A/C operation.

• Inspect the torque converter clutch (TCC) operation. (A/T only)

• Inspect deformed tire(s) that may cause surges at fixed vehicle speed range.

Checks

Action

6E-336   ENGINE CONTROL SYSTEM (4JK1/4JJ1)

Lack of Power, Sluggishness or Sponginess

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.

• Have the tire sizes changed?

• Are excessively heavy loads being carried?

• Inspect for clutch slip.

• Inspect brake drag.

• Inspect for a proper transmission shift pattern and down shift operation.

• Inspect the fuel quality (cetane index).

• Inspect the engine oil level and quality.

• Use the scan tool in order to make sure the Vehicle Speed parameter reading

matches the vehicle speedometer.

• Inspect the ECM grounds for being clean, tight, and in their proper locations.

• Inspect the programmed fuel injector ID code for each cylinder.

• Inspect the Scan Tool Data List in this section.

• Inspect the Service Bulletin.

Sensor Checks

Inspect the engine control sensors for the following conditions. Refer to the Scan Tool
Data List in this section.

• Compare the Coolant Temperature with the Intake Air Temperature (IAT) and Fuel

Temperature (FT) parameters 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 in each circuit or for a skewed sensor.

Notice: The mass air flow (MAF) sensor is heated and as a result the IAT may indicate
a higher than normal intake air temperature if the ignition switch is being ON.

• Observe the MAF parameter for a skewed or slow MAF sensor.

• Observe the Fuel Rail Pressure (FRP) Sensor parameter with the engine OFF. The

FRP Sensor should read 0.9 to 1.0 volt with the key ON and engine OFF after the
engine has stopped running for a minimum of 1 minute. If not, check for high
resistance in each circuit or for a skewed sensor.

• Observe the Fuel Rail Pressure and Desired Fuel Rail Pressure parameter between

idle and W.O.T. (accelerator pedal full travel) in Neutral. Fuel Rail Pressure
parameter should follow within 

± 5 MPa (± 725 psi) quick enough.

• Observe the Accelerator Pedal Position (APP). APP parameter should change

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

• Observe the Barometric Pressure (BARO) parameter. The BARO parameter should

indicate near surrounding barometric pressure. Refer to Altitude vs. Barometric
Pressure. (Standard output)

• Observe the Boost Pressure and BARO with ignition ON and engine OFF. Both

parameters should be within the 7.0 kPa (1.0 psi) each other. (High output)

ENGINE CONTROL SYSTEM (4JK1/4JJ1)   6E-337

Fuel System Checks

Inspect the fuel system for the following conditions. Refer to Fuel System Check chart
and appropriate procedure in the Fuel System section.

• Air in the fuel system.

• Water contamination in the fuel.

• Fuel waxing or icing.

• Fuel filter indicator lamp is continuously or frequently turned ON with engine run.

• External fuel leaks or high engine oil level.

• In-tank fuel pump operation. Refer to In-tank Fuel Pump System Check in this

section.

• Fuel leak off from the fuel pressure limiter valve and fuel injectors.

• Fuel lines between the fuel tank and fuel supply pump for being crushed, kinked,

tightness, cracks and plugged.

• A plugged fuel tank vent valve and hose.

• Inside the fuel tank for any foreign material that may be getting drawn into the fuel

line pickup causing a blocked condition.

• 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 Cylinder Balance Test with a scan tool.

• Perform the Injector Force Drive with a scan tool.

• Observe the Fuel Compensation for each cylinder at idle on the scan tool.

Air Intake System Checks

Inspect the air intake system for the following conditions.

• Air cleaner, air intake ducts and charge air cooler for a restriction, holes, or leaks.

• A restriction in the turbocharger inlet duct.

• Intake throttle valve for a stuck condition.

• A restriction or leak in the intake manifold.

• A restriction or damaged at MAF sensor.

• Perform the Swirl Control Solenoid Test with a scan tool. Inspect the diaphragm

valve operation when it commanded ON/ OFF.

• A worn or damaged turbocharger turbine wheel, shaft or compressor wheel. Refer to

turbocharger inspection in the Engine Mechanical section.

• Turbocharger wastegate valve operation. Refer to wastegate valve inspection in the

Engine Mechanical section. (Standard output)

• Turbocharger nozzle control actuator operation. Refer to Turbocharger Control

System Check in this section. (High output)

Exhaust System Checks

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

Engine Mechanical Checks

Inspect the engine mechanical for the following conditions. Refer to the Engine
Mechanical section.

• Poor cylinder compression.

• 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.

• Observe the Park/ Neutral Switch parameter with a scan tool.

• Inspect for an engine overheat condition. Refer to Engine Cooling section.

• Inspect the A/C operation.

• Inspect the torque converter clutch (TCC) operation. (A/T only).

Checks

Action

6E-338   ENGINE CONTROL SYSTEM (4JK1/4JJ1)

Hesitation, Sag or Stumble

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

• 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.

• Inspect for a proper transmission shift pattern and down shift operation.

• Inspect the fuel quality (cetane index).

• Inspect the engine oil level and quality.

• Inspect the ECM grounds for being clean, tight, and in their proper locations.

• Inspect the programmed fuel injector ID code for each cylinder.

• Inspect the Scan Tool Data List in this section.

• Inspect the Service Bulletin.

Sensor Checks

Inspect the engine control sensors for the following conditions. Refer to the Scan Tool
Data List in this section.

• Compare the Coolant Temperature with the Intake Air Temperature (IAT) and Fuel

Temperature (FT) parameters 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 in each circuit or for a skewed sensor.

Notice: The mass air flow (MAF) sensor is heated and as a result the IAT may indicate
a higher than normal intake air temperature if the ignition switch is being ON.

• Observe the MAF parameter for a skewed or slow MAF sensor.

• Observe the Fuel Rail Pressure (FRP) Sensor parameter with the engine OFF. The

FRP Sensor should read 0.9 to 1.0 volt with the key ON and engine OFF after the
engine has stopped running for a minimum of 1 minute. If not, check for high
resistance in each circuit or for a skewed sensor.

• Observe the Fuel Rail Pressure and Desired Fuel Rail Pressure parameter between

idle and W.O.T. (accelerator pedal full travel) in Neutral. Fuel Rail Pressure
parameter should follow within 

± 5 MPa ( ± 725 psi) quick enough.

• Observe the Accelerator Pedal Position (APP). APP parameter should change

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

• Observe the Barometric Pressure (BARO) parameter. The BARO parameter should

indicate near surrounding barometric pressure. Refer to Altitude vs. Barometric
Pressure. (Standard output)

• Observe the Boost Pressure and BARO with ignition ON and engine OFF. Both

parameters should be within the 7.0 kPa (1.0 psi) each other. (High output)

• Crankshaft position (CKP) sensor is tight and the sensor rotor is not damaged.