Fuel System
WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
- Check for incorrect fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - 4.0L AURORA article.
- Check for fuel contamination. See ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS WITH SPECIAL TOOL or ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS WITHOUT SPECIAL TOOL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.0L AURORA article.
Check the following that may cause the engine to run rich:
- Any water intrusion in the HO2S harness connector.
- An EVAP canister purge condition.
- Incorrect fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - 4.0L AURORA article.
- A leaking fuel pressure regulator.
- Any rich fuel injectors. See FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL or FUEL INJECTOR BALANCE TEST WITH TECH 2 under FUEL SYSTEM in SYSTEM & COMPONENT TESTS - 4.0L AURORA article.
- Inaccurate MAF sensor. See PID VALUE CHARTS In PID VOLTAGE CHARTS - AURORA article.
- Blockage on the inlet screen of the MAF sensor.
- Vacuum hoses for splits, kinks and proper connections.
- Collapsed or restricted air intake duct.
- Dirty or restricted air filter.
Check the following that may cause the engine to run lean:
- Any water intrusion into the HO2S harness connector.
- An exhaust leak between the HO2S and the engine.
- Any vacuum leaks.
- Incorrect fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - 4.0L AURORA article.
- Any lean fuel injectors. See FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL or FUEL INJECTOR BALANCE TEST WITH TECH 2 under FUEL SYSTEM in SYSTEM & COMPONENT TESTS - 4.0L AURORA article.
- An inaccurate Mass Airflow (MAF) sensor.
- Fuel contamination. See ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS WITH SPECIAL TOOL or ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS WITHOUT SPECIAL TOOL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.0L AURORA article.
- Vacuum hoses for splits, kinks and proper connections.