GM Service Manual Online
For 1990-2009 cars only

Inspection

Action

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

Preliminary Inspection

Refer to Symptoms - Engine Controls .

Fuel System Inspection

    • Inspect the fuel supply system vacuum. Refer to Fuel System Diagnosis .
    • Inspect for water contamination in the fuel. Refer to Contaminants-in-Fuel Diagnosis .
    • Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 .
    • Inspect for high fuel supply system vacuum after a cold start or during moderate or full throttle acceleration. If the vacuum jumps above specification, there is a restriction in the fuel system.

Sensor Inspection

    • Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP should be between 1.1-1.8 MPa. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
    • Test for an intermittent FRP sensor signal by wiggling the harness between the sensor and the engine control module (ECM) with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool.
    • Observe the FRP sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists.
    • Inspect for an intermittent CKP sensor signal. Refer to Intermittent Conditions .
    • Inspect the crankshaft position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.

Additional Inspection

    • Review the service bulletins for control module software updates.
    • Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
    • Inspect the generator output voltage. Refer to Charging System Test in Engine Electrical.