GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Impala 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 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 in Symptoms .
    • Refer to Visual/Physical Checks 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 improper 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 Information Sensors/Switches Description - heated oxygen sensors.
    • Check the TP sensor and related wiring.
    • Check the MAF sensor and related wiring.
    • Check the EGR system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .

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 the fuel injectors using the following procedures:
       -  Fuel Injector Balance Test
    • 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 J 26792 spark tester 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 plug, check for the following conditions:
       - Coils - Cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

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

       - Spark Plug wires - Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
600 ohms per/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 faulty.

       - Defective module
       - Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and check for the following components:
       - Fouled plugs
       - Cracks

   Important:: If carbon tracking is detected on any component replace that component and it's mate. Carbon tracking on the porcelain and pitting on the plug wire contact.

       - Improper gap
       - Burned or damaged electrodes
       - Improper heat range or reach - Refer to Spark Plug Usage in Engine Electrical.
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Oil Consumption Diagnosis in Engine Mechanical.

Check for the following intermittent ignition system conditions:

   • 

Intermittent CKP 18X signal

   • 

Intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position sensor.

   • 

Intermittent 3X reference signal

   • 

Intermittent camshaft position signal