Poor Fuel Economy

SYMPTOM DESCRIPTION:

From an actual road test the measured MPG is noticeably lower than expected. At one time the fuel economy for this vehicle was at a greater average than current measurement.


POSSIBLE CAUSE ACTION



Cooling System Malfunction Check for obvious over heating problems, low engine coolant level and leaks, water pump operation, loose belts, Faulty or incorrect thermostat, restricted air flow to radiator or restricted coolant flow, incorrect coolant solution (should be 50/50), proper fan operation (electric or belt driven).




Ignition System Malfunction Scope check Ignition System

Check IGNITION COIL for proper output voltage.

Check SPARK PLUGS for proper spark duration. Remove spark plugs, check for fuel fouled plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Replace as necessary.

Check SECONDARY CIRCUIT for abnormal firing Kv, crossfire between spark plugs (distributor cap, spark plug wires), and proper plug wire routing.

Check IGNITION TIMING for excessive spark retard.



Engine Mechanical Malfunction Check COMPRESSION Perform a compression check, and cylinder leakage test, look for weak cylinders.

Check for VACUUM LEAKS inspect Intake manifold, gasket(s), and hoses.

Check exhaust system for leaks, restriction, or damage.

Check for incorrect valve timing.



Emissions Component Malfunction Check EGR valve for binding or sticking in the open position.

Check EGR Transducer for proper operation.

Check for plugged or contaminated Catalytic Converter.



Fuel System Malfunction Check for incorrect Air-Fuel mixture, O2 Sensor, perform injector balance test, inspect regulator operation (check vacuum line and return hose), check fuel pressure.

Check for defective Fuel Pump Ballast Bypass Relay.

Check plugged or restricted Fuel Filter.

Check plugged or restricted Air Filter.

Check fuel quality.




Transmission Malfunction Check for proper transmission shift points.

Check for proper Torque Converter Clutch (TCC) operation.