Checks
| Action
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DEFINITION: The engine has a power variation under a steady throttle or cruise. There is a feeling as if the vehicle speeds up and slows down with no change in the accelerator pedal.
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Preliminary Checks
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• | Verify the driver understands the A/C compressor operation. |
• | Use a scan tool to ensure the reading of the vehicle speed sensor (VSS) matches the reading of the instrument panel speedometer. Transmission performance can be affected by incorrect VSS readings. If accuracy of the VSS is a concern, refer to
Speedometer and/or Odometer Inaccurate or Inoperative
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Sensor Checks
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• | Test for the correct operation of the manifold absolute pressure (MAP) sensor. A fixed or inaccurate MAP sensor input can cause the engine to surge. Observe the MAP sensor voltage parameter with a scan tool. Compare the MAP sensor voltage to that
of another vehicle, with the ignition ON and the engine OFF. |
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Fuel System Checks
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• | Determine if a rich or lean system can cause the condition. Drive the vehicle at the speed of the concern. Monitoring the Fuel Trim may help identify the problem. |
- | Lean--The long term fuel trim will be more than 17 percent. Refer to
DTC P0171 or P0174
. |
- | Rich--The long term fuel trim will be more than -15 percent. Refer to
DTC P0172 or P0175
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• | Test the fuel injectors. Perform the following procedures: |
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Ignition System Checks
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• | Test for the correct secondary voltage output with a
J 26792
Spark Tester. |
• | Inspect the spark plugs for correct operation and good ignition system performance. Refer to
Spark Plug Inspection
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Additional Checks
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• | Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to
Engine Controls Schematics
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• | Test the generator for the correct output voltage. |
• | Inspect for the correct operation and the correct shifting of the automatic transmission. Inspect for correct operation and engagement of the torque converter clutch (TCC). Refer to
Symptoms - Automatic Transmission
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