Symptom Definition

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Current fuel economy is noticeably lower than previous fuel economy.

Possible Causes & Corrections:

• Check for a clogged air filter.
• Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC TESTING article below.
• BASIC TESTING - 2.2L
• BASIC TESTING - 3.1L
• BASIC TESTING - 3.8L
• BASIC TESTING - 4.3L
• BASIC TESTING - 5.0L
• BASIC TESTING - 5.7L
• BASIC TESTING - 7.4L
• Check engine compression.
• Check transmission shift pattern and downshift operation.
• Check TCC system for proper operation.
• Check for dragging brakes.
• Check cooling system thermostat for proper heat range and operation.
• Ensure initial ignition timing is properly set. Check EST and ESC for proper operation.
• Remove spark plugs, and check for wet/fouled spark plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
• Check for fuel pressure too high.
• Check for fuel pressure regulator leaking into intake manifold.
• Check ECT sensor for shift in calibration. See COOLANT TEMPERATURE RESISTANCE VALUES table in the SENSOR RANGE CHARTS article in the ENGINE PERFORMANCE section.
• Check Oxygen Sensor (O2S) for silicone or lead contamination.
• Ensure speedometer is properly calibrated.
• Ensure A/C is not always on.