GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firefly (Canada) 🢒 Engine 🢒 Engine Controls - 1.3L 🢒 Hesitation, Sag, Stumble

Checks

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DEFINITION: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. Usually, the condition is more severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall if severe enough.

Preliminary Check
    • Refer to Symptoms .

Fuel System Checks
    • Check for a restriction in the fuel supply system. Check for the correct fuel pressure. Refer to Fuel System Diagnosis .
    • Perform the Fuel Injector Coil Test and the Fuel Injector Balance Test. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and to Sequential Multiport Fuel Injector Balance Test .
    • Check for water contamination of the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System Checks
    • Check for adequate secondary ignition voltage with a J 26792 spark tester or with an equivalent.
    • Check the spark plugs for any of the following conditions:
       - Wet plugs
       - A loose or bent terminal screw
       - A ceramic insulator that has cracks, carbon tracking, or deposits
       - A tip insulator that has cracks, has carbon tracking, has deposits, or is loose.
       - A center electrode that is loose
       - An incorrect spark plug gap that is too large or too small.
       - Refer to Spark Plug Visual Diagnosis in Engine Electrical.
    • Check for bare ignition wires or for shorted ignition wires.
    • Check for faulty spark plug wires.
    • Check the reference signal from the CKP sensor with a scan tool. Observe the engine speed parameter while operating the engine at the speed of the concern. The scan tool should indicate steady RPM readings and linear RPM readings while running. If sudden increases or decreases in engine speed are displayed, the engine reference signal is not stable enough for the engine to run correctly. Check for a short to ground in the ignition reference low circuit of the CKP sensor. A short to ground in the ignition reference low circuit of the CKP sensor will cause a faulty engine reference signal to be sent to the PCM. However, this will not set a CKP sensor DTC.

Additional Checks
    • Check the TP sensor for binding or for sticking. Voltage should increase at a steady rate as the throttle moves toward Wide Open Throttle (WOT).
    • Check the MAP sensor for a quick response and for an accurate response to changes in intake manifold pressure.
    • Check the EVAP control system. Refer to Evaporative Emission Control System Diagnosis .
    • Check the generator output voltage.
    • Check for exhaust system back pressure that is excessive. Refer to Restricted Exhaust System Check
    • Check the Service Bulletins for any updates.