GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 LeSabre 🢒 Transmission/Transaxle 🢒 Automatic Transaxle - 4T65-E 🢒 Hesitation, Sag, Stumble

Checks

Action

DEFINITION: Momentary 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
    • Refer to Important Preliminary Checks Before Starting in Symptoms .
    • Refer to Visual/Physical checks in Symptoms .
    • Search for bulletins.

Sensor/System
    • Check the Heated Oxygen Sensor(s). The Heated Oxygen Sensors should respond quickly to different throttle positions. If not, check the HO2S for silicon or other contaminants from fuel or use of incorrect RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Refer to Heated Oxygen Sensor(s) Information Sensors/Switches Description .
    • Check the TP Sensor and related wiring.
    • Check the MAF Sensor and related wiring.
    • Check the EGR valve for a sticking pintle. Refer to Exhaust Gas Recirculation Valve Replacement .

Fuel System
    • Check the fuel pressure.
       -  Refer to Fuel System Pressure Test (VIN K) .
       -  Refer to Fuel System Pressure Test (VIN 1) .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the injectors.
    • Check items which can cause an engine to run rich (long term fuel trim is significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich .
    • Check items that can cause an engine to run lean (long term fuel trim is significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean .

Ignition System
    • Check for proper ignition voltage output using the following steps:
       - Clip the spark tester J 26792 to engine ground.
       - Connect one end of a spark plug wire to the spark tester; leave the other end of the spark plug wire to the coil being tested.
       - Connect one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.
       - Crank the engine while observing the spark tester; a spark should be observed.
       - Repeat the above steps for each coil.
    • If spark is not present at the coil(s), check for the following conditions:

   Important:: If carbon tracking is detected on any component, replace that component and its mate.

       - Inspect the coil(s) for cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

Coil Secondary Resistance
5000 - 8000 ohms (5K - 8K ohms)

       - Inspect the spark plug wires for signs of arcing/cross firing, cracks, carbon tracking, spark plug boot damage, pinched, incorrect routing, or a resistance value greater than the specified value.

VIN 1 Spark Plug Wires Resistance
3280 - 4921 ohms per meter (1000 ohms - 1500 ohms per foot)

VIN K Spark Plug Wires Resistance
3280 - 4921 ohms per meter (1000 ohms - 1500 ohms per foot)

   Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is malfunctioning.

       - Malfunctioning ignition control module.
       - Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove the spark plugs.
    • Inspect the spark plugs for the following conditions:
       - Check the spark plug(s) for fouling. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plug for cracks.
       - Refer to Spark Plug Visual Diagnosis .

   Important:: If carbon tracking is detected on any component, replace that component and its mate.

       - Check the spark plugs for signs of carbon tracking on the porcelain or arching at the plug wire contact. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plugs for incorrect gap. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plugs for burned or damaged electrodes. Refer to Spark Plug Visual Diagnosis .
       - Check the spark plugs for incorrect heat range. Refer to Maintenance Items .
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Visual Diagnosis .