GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 LeSabre 🢒 Transmission/Transaxle 🢒 Automatic Transaxle - 4T65-E 🢒 Hesitation, Sag, Stumble

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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 Check in Symptoms .
    • Search for bulletins.

Sensor/System
    • Check the heated oxygen sensors. 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. The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Refer to Heated Oxygen Sensors in Information Sensors/Switches Description .
    • Check the throttle position (TP) sensor and the related wiring.
    • Check the mass air flow (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) .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check items which can cause an engine to run rich. Refer to DTC P0172 Fuel Trim System Rich .
    • Check items that can cause an engine to run lean. Refer to DTC P0171 Fuel Trim System Lean .

Ignition System
    • Check for the proper ignition voltage output using the following steps:
       - Clip the J 26792 spark tester to engine ground.
       - Connect one end of a spark plug wire to the J 26792 spark tester. Leave the other end of the spark plug wire to the coil being tested.
       - Connect one end of another J 26792 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 plugs, check for the following conditions:

   Important: If carbon tracking is detected on a component, replace that component and the component's mate.

       - Inspect the coils 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 more than the specified value.

Spark Plug Wires Resistance
1000 to 1500 ohms/ ft.

   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.

       - A malfunctioning ignition control module.
       - Check the ignition system wiring for a loose ignition module feed or ground connection, or damaged system wiring.
    • Remove the spark plugs.
    • Inspect the spark plugs for the following conditions:

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

       - Check the spark plugs for carbon tracking on the porcelain and the plug wire contact.
       - Check the spark plugs for fouling.
       - Check the spark plugs for cracks.
       - Check the spark plugs for incorrect gap.
       - Check the spark plugs for burned or damaged electrodes.
       - 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.
    • Check for the following intermittent ignition system conditions:
       - Check for an intermittent crankshaft position (CKP) sensor Sync or 18X signal.
       - Check for an intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position sensor.
       - Check for a intermittent 3X reference signal.
       - Check for a intermittent camshaft position signal.