Lack of Power/Sluggish/Spongy

***UPDATED BY TSB #289003, #259102.

SYMPTOM DESCRIPTION:
Engine delivers less than expected power. Little or no increase in speed, when accelerator is pushed down part way.




SYSTEM OR COMPONENT TO CHECK

COMPUTER INPUTS/OUTPUTS

CHECK:

- CONTROL UNIT: Poor connections, damaged wiring, defective or wrong control unit. Check all electrical ground circuits for good connections.
- AIR FLOW SENSOR AND CO POTENTIOMETER: Defective sensor or improper CO adjustment. Poor connections or damaged wiring to control unit.
- THROTTLE SWITCHES: Improperly adjusted, poor connection or damaged wiring to control unit, or defective switch.
- COOLANT TEMPERATURE SENSOR: Incorrect or defective sensor, poor connection, damaged wiring to control unit.
- TEMPERATURE SAFETY SWITCH (MULTIFUNCTION TEMPERATURE SENSOR): Defective switch or wiring.
- KNOCK SENSOR: Loose or defective sensor, dirt between mating surfaces, engine mechanical noise causing knock signal when no spark knock has actually occurred.
- WASTEGATE FREQUENCY VALVE: Inoperative or defective valve, poor connections or damaged wiring to control unit.

Refer to COMPUTERIZED ENGINE CONTROLS.




FUEL SYSTEM

CHECK:

- FUEL PRESSURE: Check pressure and volume output from fuel pump. Check system pressure and control pressure.
- FUEL INJECTORS: Poor spray pattern, plugged or restricted injector(s).
- FUEL DISTRIBUTOR: Sticking control plunger, incorrect basic air/fuel ratio (check idle CO content); mini filter in fuel inlet banjo bolt plugged or restricted.
- CONTAMINATED FUEL: Water or diesel in fuel
- RESTRICTED FUEL FILTER: Check filter.



IGNITION SYSTEM

CHECK:

- KNOCK SENSOR: Loose or defective sensor, dirt between mating surfaces.
- IGNITION TIMING: Check distributor basic adjustment.
- IGNITION DISTRIBUTOR, CAP, AND ROTOR: Check for cracks, arcing, moisture, rust deposits or high resistance through rotor.

Refer to IGNITION SYSTEMS.




EXHAUST SYSTEM

CHECK:

- EXHAUST RESTRICTION:

- Check turbocharger mechanical condition. Turbine and impeller should spin freely and without bearing noise.
- Check wastegate stuck open or binding. Check vacuum/pressure hoses for cracks, splits, pinches, or improper connections.




ENGINE/TRANSMISSION

CHECK:

- ENGINE COMPRESSION: Perform engine compression and cylinder leak down test. Check for leaking valves, worn piston rings (wet & dry test), or blown head gasket.
- ENGINE CAMSHAFT: Check for worn cam lobes &/or incorrect valve timing.
- TORQUE CONVERTER CLUTCH: Check operation.
- TRANSMISSION SHIFT POINTS (AUTO TRANS): Check for correct shift points/vehicle speed.
- CLUTCH OPERATION: Worn or damaged clutch disc or pressure plate.