Lack of Power/Sluggish/Spongy/Stumble

DEFINITION
Engine delivers less than expected power. Little or no increase in speed, when accelerator pedal is partially applied.

PRELIMINARY CHECKS
- Refer to Preliminary Checks. - Important Preliminary Checks
- Compare customer's vehicle with a similar unit. Make sure the customer has an actual problem.
- Remove air filter and check for dirt. or for being plugged, replace as necessary.
- Transmission shift pattern and down shift operation.
- If there is spray from only one injector on the TBI unit, there may be a malfunction in the injector assembly, or in the signal to the injector assembly. The malfunction can be isolated, by switching the injector connectors. If the problem remains with the original injector, after switching the connector, the injector is defective. Replace the injector. If the problem moves with the injector connector, the problem is an improper signal in the injector circuits. Refer to Diagnostic Charts / Chart A-3. Testing and Inspection

FUEL SYSTEM
CHECK:

- For contaminated fuel.
- For restricted fuel filter, contaminated fuel or improper fuel pressure. Refer to Diagnostic Charts / Chart A-6 Fuel System. Testing and Inspection

IGNITION SYSTEM
CHECK:

- Proper ignition voltage output with spark tester J 26792 or equivalent (ST 125).
- Ignition timing and proper operation of ignition control.

EXHAUST SYSTEM
Check exhaust system for possible restriction:

Inspect exhaust system for damaged or collapsed pipes. Inspect muffler for heat distress or possible internal failure.

1. With engine at normal operating temperature, connect a vacuum gage to any convenient vacuum port on intake manifold.
2. Operate 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 10 kPa (3 in. of Hg) from reading at 1000 RPM, the exhaust system should be inspected for restrictions.
5. Disconnect exhaust pipe from engine and repeat Steps 3 and 4. If vacuum still drops more than 10 kPa (3 in. of Hg) with exhaust disconnected, check for exhaust manifold restriction and valve timing.

ADDITIONAL CHECKS
CHECK:

- Control module grounds for being clean, tight, and in their proper location.
- Exhaust Gas Recirculation (EGR) operation for being open or partly open all the time.
- Torque Converter Clutch (TCC) operation.
- A/C operation.
- Generator output voltage. Repair if less than 9 volts or more than 16 volts.

ENGINE MECHANICAL
Check engine compression, valve timing, and for proper or worn camshaft.