GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Monte Carlo 🢒 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
    • 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 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 Sensor(s).
    • 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 .
    • 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 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 plugs(s), check for the following conditions:
       - Inspect the coil(s) for cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

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

       - Inspect the spark plug wires for 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 malfunctioning.

       - Inspect for a malfunctioning ignition control module.
       - Inspect the ignition system wiring for loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and check for the following:
       - 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
       - Wear
       - Improper gap
       - Burned or damaged electrodes
       - Improper heat range or reach. 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:
       - CKP Sync or CKP 18X Signal.
       - Ignition Feed circuit or sensor ground circuit to the crankshaft position sensor or camshaft position sensor.
       - 3X reference signal.
       - camshaft position signal,