Is a Short-Term Fuel Trim of 99% Normal?
2 Answers
Whether a short-term fuel trim of 99% is normal mainly depends on whether the sum of long-term and short-term trim values exceeds 5%. If it exceeds 5%, it is considered abnormal. Factors affecting short-term fuel trim in the engine: Factors influencing the fuel trim coefficient include engine misfire, poor exhaust flow, low fuel pump pressure, or clogged fuel injectors. These aspects should be checked first. Troubleshooting short-term fuel trim issues: You can check for clogged injectors, eroded spark plugs, poor fuel quality, faulty mass air flow sensors, or overdue fuel filter replacement.
Short-term fuel trim reaching 99% usually indicates an abnormality, suggesting the engine control system is continuously increasing fuel supply to compensate for certain issues. This could be caused by vacuum leaks, faulty mass airflow sensors, damaged oxygen sensors, or insufficient fuel pressure, among other factors. If left unaddressed, it may lead to increased fuel consumption, potential exhaust emissions exceeding standards, and even accelerated engine wear. It's advisable to first check if the air filter is clogged, as a dirty air filter restricts airflow, prompting the ECU to add more fuel. Additionally, using an OBD scanner to read fault codes can help narrow down the problem. If the issue persists, consulting a professional technician for diagnosis is recommended to prevent minor problems from escalating into major repairs. For DIY attempts, ensure all hoses and connections are properly sealed, without cracks or looseness.
