GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Cavalier (CNG) 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 Poor Fuel Economy

Checks

Action

DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Preliminary Checks
    • Refer to Symptoms .
    • Inspect the air cleaner element (filter) for dirt or for being plugged.
    • Visually and physically inspect the vacuum hoses for splits, kinks and the proper connections as shown on the Vehicle Emission Control Label.
    • Ask the operator if driving habits include the following items:
       - Is the A/C ON full time (defroster mode ON)?
       - Is there excessive idling or stop-and-go driving?
       - Are the tires at the correct air pressure?
       - Is the CNG fill pressure low (inspect fill station pressure)?
       - Are excessively heavy loads being carried?
       - Is acceleration too heavy or too often?
    • Suggest to the operator to fill the fuel tank and to verify the fuel economy again.

Fuel System Checks
    • Verify the fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect the fuel system for leakage.

Sensor Checks
    • Inspect the engine coolant temperature (ECT) sensor with the scan tool. Compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than five degrees greater or less than the ambient air temperature on a cold engine, inspect for high resistance in the ECT sensor circuit. Refer to Temperature vs. Resistance in Engine Controls - 2.2L in the J Platform Service Manual. If the ECT sensor resistance is not within specification, refer to DTC P0118 ECT Sensor Circuit High Voltage or DTC P0117 ECT Sensor Circuit Low Voltage in Engine Controls - 2.2L in the J Platform Service Manual.
    • Verify proper operation of the MAP sensor.
    • Verify proper operation of the TP sensor.
    • Inspect the EGR system for the following conditions:
       - Vacuum leaks in the EGR pipes and the adapter.
       - A stuck open pintle in the EGR valve.

Ignition System Checks

CNG is a gaseous fuel. It requires higher secondary ignition system voltage for the equivalent gasoline operating conditions. If a problem is reported during CNG operation but not during gasoline operation, do not discount the possibility of a CNG-only ignition system failure. Test the system accordingly.

    • Verify the proper ignition output voltage using the J 26792 or the equivalent.
    • Inspect the spark plugs. Remove the plugs and inspect them for the following conditions:
       - Wet plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned electrodes
       - Heavy deposits
    • Inspect the spark plug wires for proper resistance and condition.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect for loose ignition coil connections.
    • Inspect for loose engine control module grounds.
    • Inspect for loose ignition control module grounds.

Cooling System Checks
    • Verify the engine coolant level.
    • Inspect the engine thermostat for always being open or for the wrong heat range. Refer to Thermostat Diagnosis in Engine Cooling in the J Platform Service Manual.

Additional Checks
    • Verify the transmission shift pattern. Refer to Range Performance in Automatic Transaxle - 3T40 or Automatic Transaxle - 4T40-E in the J Platform Service Manual.
    • Verify the proper torque converter clutch (TCC) operation. Refer to Torque Converter Clutch Diagnosis in Automatic Transaxle - 3T40 or Automatic Transaxle - 4T40-E in the J Platform Service Manual.
    • Inspect the exhaust system for possible restrictions and the following conditions:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the muffler for signs of heat distress or for possible internal failure.
       - Inspect for a possible plugged three-way catalytic converter. Refer to Restricted Exhaust System Check in Engine Controls - 2.2L in the J Platform Service Manual.

If all the procedures have been completed and no malfunction has been found, review and inspect the following items:

    • Visually and physically inspect all electrical connections within the suspected circuit and systems.
    • Verify scan tool data.
    • Inspect for dragging brakes. Refer to Brake System Diagnosis in Hydraulic Brakes in the J Platform Service Manual.