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.




SYSTEM OR COMPONENT TO CHECK ACTION

FUEL CHECK: ^ FUEL TYPE, quality and alcohol content.
^ FUEL PRESSURE: use CHART A-4A in
DIAGNOSTIC CHARTS/A-CHARTS
NOTE: To determine if the condition is caused by
a RICH system, the vehicle should be driven at the
speed of the complaint. If closed loop is achieved,
the fuel system has to checked for rich, lean or
improper fuel control. The DFI system has ECM
parameter ED19 "Integrator" which monitors the
oxygen sensor rich lean status and drives the fuel
system richer if the 02 sensor is lean or
leaner if the sensor is rich.
To help identify the problem
Refer to DFI SYSTEM CHECK. Or codes
E45 and EO45 for rich condition
NOTES ON INTERMITTENTS




IGNITION 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 for cracking, hardness, and
proper connections.
^ EST operation.
^ IGNITION TIMING.



COOLING CHECK: ^ For obvious over heating problems.
^ Low engine coolant level and leaks.
^ Water pump operation, loose belts
^ Restricted air flow to radiator or
restricted coolant flow.
^ Faulty or incorrect thermostat.
^ Correct coolant solution - should be a 50/50
mix of anti-freeze (coolant) and water.
^ Fan operation (electric or belt driven).





MECHANICAL - ENGINE/TRANSMISSION CHECK: ^ Transmission shift pattern.
^ VCC operation. The "Diagnostic Display" should
indicate an rpm drop when the VCC is
commanded "ON."
^ For proper calibration of speedometer.
^ For dragging brakes.
^ For proper tire inflation.