Isuzu KB P190. Manual - part 325

6E-266  Engine Control System (4JH1) 

Lack of Power, Sluggishness, 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 (A/T only). 
• 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 engine control module (ECM) and fuel injection pump control unit (PCU) 

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

• Inspect the scan tool 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 scan tool 
Data List in this section. 
• Use the scan tool 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 scan tool 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 scan tool to observe the Accelerator Pedal Position Accelerator Pedal 

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

Engine Control System (4JH1)  6E-267 

Checks Action 

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 scan tool 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. 

• 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. 

6E-268  Engine Control System (4JH1) 

Checks Action 

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

 
 

Hesitation, Sag, 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 scan tool 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. 

Sensor Checks 

Inspect the engine control sensors for the following conditions. Refer to the scan tool 
Data List in this section. 
• Use the scan tool 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 scan tool 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 scan tool to observe the Accelerator Pedal Position Accelerator Pedal 

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

Engine Control System (4JH1)  6E-269 

Checks Action 

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 scan tool 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. 

• 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.