Lack Of Power, Sluggishness Or Sponginess . 1A-334 - Isuzu N 2008 Series Workshop Manual

1A-334 Engine Control System (4JJ1)
Lack of Power, Sluggishness or Sponginess
Checks
Definition:
The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator
pedal.
Preliminary Checks
Sensor 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.
Inspect the engine control sensors for the following conditions. Refer to 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 Fuel Rail Pressure (FRP) Sensor parameter with the engine OFF. The
FRP Sensor should read 0.9 to 1.0 volt with the ignition switch 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 Boost Pressure and Barometric Pressure (BARO) with ignition ON and
engine OFF. Both parameters should be within the 7.0 kPa (1.0 psi) each other.
Action