Isuzu 4ja1, Workshop Manual

Page: 502 / 564

6E-248 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.