Lack of Power, Sluggishness, or Sponginess

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Checks	Action
DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal.
Preliminary Checks	Refer to Important Preliminary Checks in Symptoms - Engine Controls . IMPORTANT: Do not compare the power output of the vehicle while operating on CNG to a vehicle operating on gasoline. Both fuels have different drive feel characteristics. Verify the customers concern by comparing the power output of a similarly equipped known good vehicle to the suspect vehicle. Inspect the air filter for proper type and for dirt or restriction. Test the transmission for proper shift pattern and downshift operation. Inspect the PCM for the correct CNG calibration. Program the PCM if necessary.
Fuel System Checks	Test for proper fuel system pressures. Refer to Fuel System Diagnosis . Inspect the high pressure regulator (HPR) filter for restriction. Refer to High Pressure Regulator (HPR) Filter Replacement .
Ignition System Checks	IMPORTANT: A higher secondary ignition voltage is required to operate the vehicle on CNG than on gasoline. Test for proper secondary ignition system voltage output using only the J 26792 Spark Tester. IMPORTANT: More timing advance is required to operate the vehicle on CNG than on gasoline. Test for proper operation of the Knock Sensor system.
Exhaust System Checks	Inspect the exhaust system for a possible restriction. Restrictions can include the following: A failed catalytic converter Damaged or collapsed pipes An internally failed muffler - may show signs of heat distress
Engine Mechanical Checks	Test for proper engine operation by checking for the following: Correct engine compression Correct engine valve timing A worn or incorrect camshaft
Additional Checks	Test for proper A/C compressor clutch operation. An A/C clutch that is engaged all the time may cause this symptom. Test for proper transmission torque converter clutch (TCC) operation, if equipped. Test for proper generator operation. Inspect for proper operation of the accelerator pedal. A stretched accelerator cable may cause this symptom.