Poor Fuel Economy

Symptom: 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 SECONDARY CIRCUIT firing Kv and spark duration.
SEE IGNITION SYSTEM/OSCILLOSCOPE PATTERNS.

- Remove spark plugs and inspect for: cracks, excessive wear, improper gap, burned electrodes, and wet or heavy deposits. Replace as necessary.

- Inspect distributor cap, rotor and spark plug wires for proper plug wire routing, crossfire between spark plugs (in cap) or wires, wires shorting to ground and rotor shorting to ground via distributor shaft.

- Check IGNITION TIMING for excessive spark retard.
SEE IGNITION SYSTEM/ TIMING SPECIFICATIONS

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 for plugged or contaminated Catalytic Converter.

FUEL SYSTEM MALFUNCTION - Check plugged or restricted Air Filter.

- Check fuel system pressure and volume.

- Check for lean Air-Fuel mixture, (O2S Sensor output).

- Perform injector balance test.

- Check fuel quality.

- Check Throttle Position Sensor for proper operation.

TRANSMISSION MALFUNCTION - Check for proper transmission shift points.

- Check for proper Torque Converter Clutch (TCC) operation.