DIAGNOSING POOR FUEL ECONOMY
by Mark Davidson

SYMPTOM SUMMARY
The vehicle runs normally however, fuel economy is lower than it was at one time. If the vehicle runs poorly refer to the specific running symptom for further diagnostic information. Any running or performance problems should be diagnosed prior to using this symptom’s diagnosis.

USUAL CAUSE
Poor fuel economy can be caused by a multitude of problems. Driving habits and enviroments play a significant role in fuel economy. Prior to diagnosing this symptom, you should drive for at least two full tanks of gas to ensure there is a problem rather than an intermittent condition, such as mountainous driving. Poor fuel economy is usually the result of lack of routine maintenance.

DIAGNOSIS
You should start your diagnosis by determining what service has been performed on the vehicle. Routine spark plug replacement is necessary to maintain good fuel economy. Spark plugs provide the ignition source to initiate the combustion process to burn the fuel. If the spark plugs are worn they will not provide a good ignition source for the fuel and can degrade the fuel economy. The air filter filters the air that enters the engine. It is designed to remove the harmful dust and debris that would otherwise enter the engine. An air filter that is only partially plugged can restrict the air entering the engine and reduce the fuel economy. Inspect the air filter and replace it even it is only moderately dirty. A new filter can go a long way in improving fuel economy. Do not attempt to blow out the filter with compressed air. New filters rely on small fibers to “grab” the incoming dirt particles. Blowing out the filter will remove these fibers and reduce the filters affectiveness. Tire inflation should be checked. Low tire pressure can reduce fuel economy drastically. Tires provide the necessary traction to prevent the vehicle from skidding and slidding. At the same time, tires provide a low rolling resistance so that the engine can easily propel the vehicle. If the tires are low, the rolling resistance is increased and will require the engine to consume more fuel to generate the same amount of power. You should ensure the tires are inflated evenly and to the proper pressure. Proper ignition timing is critical to maintain good fuel economy. Most newer vehicles have computer controlled ignition timing. On these systems, the timing is not adjustable. On vehicles that have adjustable ignition timing the timing should be checked. You should consult the underhood emission control label for instructions on ignition timing adjustments. Engine oil can also affect your vehicles fuel economy. You should ensure you are using a multi-viscosity oil as recommended by your vehicles manufacturer.

PRECAUTIONS, TIPS, and NOTES
Consult your owners manual for recommended service intervals and maintenance schedules for your driving conditions. Also refer to the “Vehicle Maintenance Tips” article for more information on preventative maintenance.

(Mark gave up on sports when the Browns left Cleveland and now spends his Sundays working under a shade tree in the back yard tuning his son’s soap box derby car.)