Hesitation, Sag, Stumble
DEFINITIONMomentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.
PRELIMINARY STEPS
^ Refer to Important Preliminary Checks and Visual and Physical Checks before starting.
^ Search for Technical Service Bulletins.
^ Check PCM grounds for being clean, tight and in their proper locations. Refer to Diagrams / Powertrain Control Module for PCM ground numbers and locations.
SENSOR/SYSTEM
^ Check Manifold Absolute Pressure (MAP) sensor operation.
^ Check Exhaust Gas Recirculation (EGR) for being loose or for a faulty gasket. Check EGR operation for being open all the time.
^ Using a Scan Tool, monitor Throttle Position (TP) sensor voltage. The TP sensor voltage should be less then 0.9 volt. If the TP sensor voltage is greater than 0.9 volt, inspect the Acceleration Slip Regulation (ASR)/Traction Control System (TCS) adjuster assembly (If so equipped). Also inspect throttle body and accelerator cables for binding. Refer to Adjuster Assembly Throttle And Cruise Control Cables.
FUEL SYSTEM
^ Check for low fuel pressure. Refer to Fuel System Diagnosis.
^ Check for restricted fuel filter. Refer to Fuel System Diagnosis.
^ Check for contaminated fuel. Refer to Alcohol/Contaminants-In-Fuel Test.
^ Check injector fuse(s) for being open. An open injector fuse will cause the injectors not to operate. Replace fuse and inspect injector circuits for an intermittent short to ground.
^ Perform injector balance test. Refer to Fuel Injector Balance Test.
^ Check items which can cause an engine to run rich (long term fuel trim near -14%). For a Rich condition, refer to DTCs:
P0132 HO2S Circuit High Voltage Bank 1 Sensor 1
P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
^ Check items that can cause an engine to run lean (long term fuel trim near 22%). For a Lean condition. refer to DTCs:
P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1
P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1.
IGNITION SYSTEM
^ Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look/Listen for arcing or misfiring as water is applied.
^ Check for proper ignition voltage output with spark tester J 26792. Refer to Distributor Ignition System Check for procedure.
^ Remove spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
^ An improper spark plug gap will cause a driveability problem. Refer to Spark Plug / Specifications for correct gap.
^ The spark plug gapping should be done using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement.
^ If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. To determine the rich condition, refer to DTCs:
P0172 Fuel Trim System Rich Bank 1
P0175 Fuel Trim System Rich Bank 2.
For the oil fouling condition, refer to Engine.
^ Check for loose ignition coil ground. Refer to Distributor Ignition System Check.
^ Spark plugs for proper heat range. Refer to Owners Manual or Spark Plug / Application and ID.
^ Check distributor vent system for being restricted or open. Refer to Distributor Vent System Check.
ENGINE COOLING SYSTEM
^ Check the engine thermostat for functioning correctly and for proper heat range. Refer to Engine Cooling.
ADDITIONAL CHECKS
^ Check generator output voltage. Refer to Starting and Charging / Charging System for procedure. Repair if less than 9 or more than 16 volts.