Lack of Power/Sluggish/Spongy/Stumble

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

PRELIMINARY CHECKS
Perform the careful visual and physical checks as described in Preliminary Checks. Testing and Inspection

^ Compare customer's vehicle to similar unit. Make sure the customer has an actual problem.

^ Remove air filter and check air filter for dirt, or for being plugged, replace as necessary.

^ If there is spray from only one injector, there is either 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 Chart A-3 Engine Cranks But Will Not Run. Related Tests, Information and Procedures

IGNITION SYSTEM
Check: Proper ignition voltage output with spark tester J26792 (ST-125).

Check: Ignition timing. See underhood "Vehicle Emission Control Information" label.

Check: Proper operation of Ignition Control (IC). Refer to Chart C-4 Distributor Ignition System Check. Chart C-4 Distributor Ignition (DI) System Check

EXHAUST SYSTEM
Check: Exhaust system for possible restriction. Refer to Chart B-1 Restricted Exhaust System Check. Inspect exhaust system for damaged or collapsed pipes. Inspect muffler for heat distress or possible internal failure. B Charts

1. With engine at normal operating temperature, connect a vacuum gage 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 steady 2500 RPM.

4. If vacuum at 2500 RPM decreases more than 3 inch Hg, from reading at 1000 RPM, the exhaust system should be inspected for restrictions.

5. Disconnect exhaust pipe from engine and repeat Steps 3 & 4. If vacuum still drops more than 3 inch Hg, with exhaust disconnected, check valve timing.

ADDITIONAL CHECKS
Check: Engine Control Module (ECM) grounds for being clean, tight, and in their proper location.

Check: EGR operation for being open, or partly open, all the time. Refer to Chart C-7 Exhaust Gas Recirculation System. Chart C-7 EGR System Check

Check: [1][2]Torque Converter Clutch (TCC) operation. Refer to Chart C-8 Torque Converter Clutch System. Chart C-8 Torque Converter Clutch (TCC) Diagnosis

Check: Generator output voltage. Repair if less than 9 volts or more than 16 volts.

ENGINE MECHANICAL
Check: Engine compression, valve timing and for a proper or worn camshaft. Refer to Engine/Specifications/Mechanical. Specifications