| DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position. |
| Preliminary |
- Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .
- Search for bulletins.
- Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views
in Wiring Systems and Engine Controls Schematics
.
- Verify the driver understands the operation of the transmission torque converter clutch (TCC) and A/C compressor operation as explained in the owners manual.
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| Sensor/System |
- Inspect the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions. If they do not, inspect the HO2S for silicon or other contaminates from fuel or the use of improper RTV sealant. The sensors may have a white, powdery coating and result in a high but false signal voltage rich exhaust indication. The PCM will then reduce the amount of fuel delivered to the engine causing a severe driveability problem.
- Inspect for the following that may cause the engine to run rich:
- Inspect for the following conditions that may cause the engine to run lean:
- Inspect for an engine coolant temperature (ECT) sensor that has shifted in value. Refer to Temperature vs Resistance
.
- Inspect for proper operation of the manifold absolute pressure (MAP) sensor. Refer to Altitude vs Barometric Pressure
.
- Test the crankshaft position (CKP) sensor for an internal short. Refer to Crankshaft Position Sensor (CKP) System Diagnosis .
|
| Fuel System |
|
| Ignition System |
- In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:
- Remove spark plugs and inspect for the following conditions:
- Correct heat range
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
- Verify that the spark plugs are of the correct type.
- Inspect for proper ignition voltage output with the J 26792
HEI Spark Tester. See Special Tools
.
- An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool.
- Determine the cause of the fouling before replacing the spark plugs.
- Inspect for damaged or misaligned spark plug boots.
- Inspect the electronic ignition (EI ) module for proper ground connection.
- Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300
.
|
| Engine Mechanical |
Inspect for excessive crankshaft endplay that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearings Cleaning and Inspection
in Engine Mechanical. This could result in any of the following conditions:
- A no start
- A start and stall
- Erratic performance
|
| Additional Inspections |
- Visually and physically inspect vacuum hoses for splits, kinks, and proper connections and routing as shown on the Vehicle Emission Control Information label.
- Inspect the transmission torque converter clutch (TCC) operation. A TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic Starting Point - Automatic Transmission
in Automatic Transaxle 4T40-E/ 4T45-E.
- Test the A/C clutch for proper operation. Refer to Symptoms - HVAC Systems - Manual
in HVAC Systems-Manual.
- Inspect the exhaust system for possible restrictions. Refer to Restricted Exhaust
in Engine Exhaust.
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