GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Prizm 🢒 Engine 🢒 Engine Controls - 1.8L 🢒 Poor Fuel Economy

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 .
    • Check the air cleaner element for dirt or restrictions.
    • Visually and physically check the vacuum hoses for splits, kinks, and proper connections as shown on the Vehicle Emission Control Information label.
    • Check the owners driving habits for any of the following:
       - The A/C system defroster mode is ON all the time
       - The tires are improperly inflated
       - Heavy loads are frequently being carried
       - Heavy acceleration and high speeds are common
       - Frequent short trips
       - Prolonged periods of idling
       - Driving on unpaved or rough roads
    • Suggest that the owner refill the fuel tank and recheck the fuel economy.

Fuel System Checks
    • Check the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy. Refer to Fuel System Specifications and Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check for the correct fuel pressure. Refer to Fuel System Diagnosis .

Ignition System Checks
    • Check the spark plugs for any of the following conditions:
       - Any wet or fuel fouled plugs
       - A terminal screw that is bent or loose
       - A ceramic insulator that has cracks, carbon tracking, or deposits
       - A tip insulator that has cracks, carbon tracking, deposits or is loose
       - A center electrode that is loose
       - An incorrect spark plug gap
       - Any missing platinum pads
    • Check the ignition coil boots for cracking, chafing, and loose connections.
    • Observe the Spark parameter on the scan tool at idle, while operating the rear defogger, the A/C system, or the headlights. If the scan tool display remains fixed at 10 degrees, check for a short to ground in the Diagnostic Request circuit from the PCM connector C2 terminal 15 to the underhood diagnostic link connector.
    • Check the knock sensor and the sensors circuit shielding. The knock sensor is not diagnosed for excessive activity. A faulty knock sensor or signal interference could cause excessive retard of the ignition timing advance. Observe the Spark parameter on a scan tool and compare with a known good vehicle. A typical value in OD at 65 mph is 26-32 degrees.

Cooling System Checks
    • Check the engine coolant level.
    • Check the engine thermostat for always being open or for the wrong heat range.

Additional Checks
    • Check the clutch adjustment in vehicles equpiied with a manual transmission.
    • Check the transmission shift pattern and the TCC operation in vehicles equipped with an automatic transmission.
    • Check for dragging brakes.
    • Check for uneven or premature tire wear. A suspension misalignment can cause reduced fuel economy.
    • Verify that the tires and wheels are similar to OEM. Wide performance tires create more drag and taller tires can cause odometer discrepancies.
    • Check for the speedometer for proper calibration.
    • Check for a green engine. Fuel economy may not be near expected levels until the engine has had 5 000 to 8 000 km (3,000 to 5,000 miles) to break in.
    • Check for add-on equipment like luggage racks and carriers. Wind resistance can lower fuel economy.
    • Check the Service Bulletins for any updates or information.