Poor Fuel Economy

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



SYSTEM OR COMPONENT TO CHECK

FUEL SYSTEM

CHECK:


- FUEL TYPE: Fuel quality and alcohol content.
- FUEL PRESSURE: System pressure too high, control pressure too low. Check for restricted fuel return line or defective pressure regulator.
- FUEL INJECTOR: Leaking or sticking injector
- COLD START INJECTOR: Leaking.


COMPUTER INPUTS/OUTPUTS

CHECK:

- CONTROL UNIT: Check for correct control unit and connections.
- DIFFERENTIAL PRESSURE REGULATOR: Damaged or defective regulator, or wiring to control unit.
- OXYGEN SENSOR: Check output voltage, wiring and connections.
- AIR FLOW SENSOR POTENTIOMETER: Defective sensor, trim screw out of adjustment, poor connections or damaged wiring to control unit.



IGNITION SYSTEM

CHECK:

- SPARK PLUGS: Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.
- IGNITION WIRES: check for cracking, hardness, and high secondary resistance or incorrect firing order.
- KNOCK SENSOR: Defective sensor, dirt between mating surfaces, poor connections to control unit.
- IGNITION TIMING: Check distributor basic adjustment.
- IGNITION DISTRIBUTOR, CAP, AND ROTOR: Check for cracks, arcing, moisture, rust deposits or high resistance through rotor.



COOLING SYSTEM

CHECK: For obvious over heating problems.

- AUXILIARY COOLING FAN: Temperature switch defective or damaged wiring to control unit.
- ENGINE COOLANT: Low engine coolant level and/or leaks, coolant solution - should be a 50/50 mix of anti-freeze (coolant) and water.
- WATER PUMP: Loose belts?
- RADIATOR: Restricted air flow to radiator or restricted coolant flow through radiator.
- THERMOSTAT: Faulty or incorrect.



MECHANICAL

CHECK:

- COMPRESSION:
- Clutch slipping.
- For dragging brakes.
- For proper tire inflation.