For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: The engine delivers less than expected power. Little increase in speed, or a total lack of acceleration when the accelerator pedal is pushed down part way.
Preliminary Inspections |

• | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .

• | Search for bulletins.

• | Inspect the engine control module (ECM) grounds for being clean, tight and in the proper locations. Refer to Engine Controls Schematics .

• | Remove the air filter element and inspect for dirt or for being restricted.

• | Inspect the intake air ducts for the following conditions:

- | Restrictions

- | Improperly installed hoses

- | Leaks

- | Collapsed hoses

Fuel System |

• | Inspect the fuel system. Refer to Fuel System Diagnosis .

• | Test for incorrect fuel pressure.

• | Test for a restricted fuel filter.

• | Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Test the fuel injectors. Refer to Fuel Injector Balance Test with Special Tool and Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

• | Inspect the items which can cause an engine to run rich (long term fuel trim near -13 percent). For a rich condition, refer to DTC P0172 or P0175 .

• | Inspect the items that can cause an engine to run lean (long term fuel trim near 23 percent). For a lean condition, refer to DTC P0171 or P0174 .

Sensor/System |

• | Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Detonation/Spark Knock .

• | Check for proper operation of the throttle control system components. Use the scan tool special functions to actuate the system. Verify that the throttle opens to 100 percent. With a scan tool, monitor the following throttle control system components:

- | Throttle position (TP) sensors

- | Accelerator pedal position (APP) sensors

- | Throttle actuator

Ignition System |

• | Test for proper ignition voltage output with a J 26792 Spark Tester . Refer to Electronic Ignition (EI) System Diagnosis .

• | Test for secondary ignition leakage. Refer to the procedure in the Diagnostic Aids portion of Electronic Ignition (EI) System Diagnosis .

• | Remove the spark plugs and inspect for the following conditions:

- | Correct heat range

- | Wet plugs

- | Cracks

- | Wear

- | Improper gap

- | Burned electrodes

- | Heavy deposits

• | An improper spark plug gap will cause a driveability concern. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement .

• | Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant or oil fouled. Refer to Spark Plug Inspection . Once you determine the cause of the fouling, refer to one of the following procedures:

- | For diagnosis of a rich condition, refer to DTC P0172 or P0175 .

- | For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling.

- | For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical-3.0 (L81).

Engine Mechanical |

• | Excess oil in combustion chamber due to leaking valve seals--Refer to Oil Consumption Diagnosis in Engine Mechanical-3.0L (L81).

• | Check for incorrect camshaft timing. Refer to Timing Belt Timing Adjustment in Engine Mechanical-3.0L (L81).

• | Inspect the following components for incorrect basic engine parts:

- | Camshafts--Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical-3.0L (L81).

- | Cylinder heads--Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical-3.0L (L81).

- | Pistons, connecting rods or bearings--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection in Engine Mechanical-3.0L (L81).

Additional Inspections |

• | Inspect the following components of the exhaust system for possible restrictions:

- | The exhaust system for physical damage

- | The mufflers for heat distress or possible internal failure

- | The catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine--Refer to Restricted Exhaust in Engine Exhaust.

• | Test for proper operation of the intake resonance switchover valve and the intake plenum switchover valve. Refer to Intake Manifold Runner Control System Diagnosis .

• | Test the transmission torque converter clutch (TCC) for proper operation. Refer to Torque Converter Diagnosis in Automatic Transmission-4L30-E.

• | Check for other transmission related faults that might cause the transmission to operate in a default mode. Refer to Diagnostic System Check - Automatic Transmission Shift Lock Control in Automatic Transmission-4L30-E.