Isuzu KB P190. Manual - part 323

6E-258  Engine Control System (4JH1) 

Checks Action 

Electromagnetic Interference (EMI) 
and Electrical Noise 

Some electrical components/circuits are sensitive to EMI or other types of electrical 
noise. Inspect for the following conditions: 
• A misrouted harness that is too close to high voltage/high current devices such as 

injection components, motors, generator etc. These components may induce 
electrical noise on a circuit that could interfere with normal circuit operation. 

• Electrical system interference caused by a malfunctioning relay, or the engine control 

module (ECM) driven solenoid or switch. These conditions can cause a sharp 
electrical surge. Normally, the problem will occur when the malfunctioning 
component is operating. 

• Improper installation of non-factory or aftermarket add on accessories such as lights, 

2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell 
phones, etc. These accessories may lead to an emission related failure while in use, 
but do not fail when the accessories are not in use. 

• Test for an open diode across the A/C compressor clutch and for other open diodes. 

Some relays may contain a clamping diode. 

• Test the generator for a bad rectifier bridge that may be allowing AC noise into the 

electrical system. 

Incorrect ECM Programming 

• There are only a few situations where reprogramming a ECM is appropriate:  
Important: 
DO NOT reprogram the ECM with the SAME software/calibration files that are already 
present in the ECM. This is not an effective repair for any type of driveability problem. 

- A ECM from another vehicle is installed. 
- Revised software/calibration files have been released for this vehicle. 

• Verify that the ECM contains the correct software/calibration. If incorrect 

programming is found, reprogram the ECM with the most current 
software/calibration. 

Duplicating Failure Conditions 

• If none of the previous tests are successful, attempt to duplicate and/or capture the 

failure conditions. 

• An alternate method is to drive the vehicle with the DMM connected to a suspected 

circuit. An abnormal reading on the DMM when the problem occurs, may help you 
locate the problem. 

scan tool Snapshot 

The scan tool can be set up to take a Snapshot of the parameters available via serial 
data. The Snapshot function records live data over a period of time. The recorded data 
can be played back and analyzed. The scan tool can also graph parameters singly or 
in combinations of parameters for comparison. The Snapshot can be triggered 
manually at the time the symptom is noticed, or set up in advance to trigger when a 
DTC sets. 
An abnormal value captured in the recorded data may point to a system or component 
that needs to be investigated further. 
Refer to the scan tool user instructions for more information on the Snapshot function. 

 
 

Hard Start 

Checks Action 

DEFINITION:The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but 
immediately dies. 
Preliminary Checks  

• Diagnostic System Check - Engine Controls. 
• Ensure the driver is using the correct starting procedure. 
• 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 scan tool Data List in this section. 
• Inspect the Service Bulletins for ECM software updates. 

Engine Control System (4JH1)  6E-259 

Checks Action 

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

is not damaged. 

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. 

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-260  Engine Control System (4JH1) 

Checks Action 

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 (timing gear) 
• Improper valve gap 
• Broken or weak valve springs 
• Worn camshaft lobes 

Electrical System Checks  

Inspect the engine electrical for the following conditions. Refer to the Engine Electrical 
section. 
• Inspect the glow plug control (preheating) system operation. 
• Inspect for slow cranking speed. 
• Inspect for weakened batteries. 

 
 

Rough, Unstable, or Incorrect Idle And Stalling 

Checks Action 

DEFINITION:Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. 
Either condition may be severe enough to stall the engine. 
Preliminary Checks 

• Diagnostic System Check - Engine Controls. 
• Remove the air cleaner and check for dirt, or for air ducts being plugged or restricted. 

Replace as necessary. 

• 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 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.  

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

not damaged. 

Engine Control System (4JH1)  6E-261 

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. 
d. Connect the clear hose to the fuel injection pump. 
c. 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. 

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.