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.
- KNOCK SENSOR: Loose or defective sensor, dirt between mating surfaces, engine mechanical noise causing knock signal when no spark knock has actually occurred.

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:

1. With engine at normal operating temperature, connect a vacuum gauge to any convenient vacuum port on intake manifold.
2. Run engine at 1000 rpm and record vacuum reading.
3. Increase rpm slowly to 2500 rpm. Note vacuum reading at a steady 2500 rpm.
4. If vacuum at 2500 rpm decreases more than 3" Hg, from reading at 1000 rpm, the exhaust system should be inspected for restrictions.
5. Disconnect exhaust pipe from engine and repeat step 3 & 4. If vacuum still drops more than 3" Hg, with exhaust disconnected, check for exhaust manifold restriction and/or incorrect valve timing.




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.