Engine Control System (4HK1) 1A-359
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 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.
• Crankshaft position (CKP) sensor is tight and the sensor rotor is not
damaged.
LG4HKED-WE-0871.book 359 ページ ２００７年１１月２９日 木曜日 午後６時２９分
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