Is a Long-Term Fuel Trim of -14.7 Rich or Lean?
3 Answers
Long-Term Fuel Trim -14.7 indicates a rich condition. Below is relevant information: 1. Fuel Standard: Generally, the long-term fuel trim parameter ranges from -23% to 16%. A value of 0 means the fuel supply does not require compensation to achieve the correct mixture concentration. A positive value indicates that the injection system needs to inject additional fuel, meaning the engine's air-fuel mixture is lean, and the vehicle may have difficulty starting. A negative value means the fuel injection system needs to reduce fuel delivery to correct an overly rich mixture. Therefore, when the long-term fuel trim is negative, it indicates the vehicle's mixture is too rich. 2. Long-Term Fuel Trim Standard: Typically ±5%. If it exceeds this range, it is highly likely that the engine has a fault. If the vehicle's fuel injectors are clogged, both the fuel injection volume and atomization effect will be poor, resulting in a lean combustible mixture in the engine cylinders.
As a seasoned driver with years of experience, I recall a time when my car showed similar readings. A long-term fuel trim displaying a negative value, like this -14.7%, indicates that the engine's air-fuel mixture is too rich. This means there's too much fuel being injected and not enough air, so the ECU is working hard to reduce fuel supply to balance it. This is common in older car models or when there's carbon buildup in the fuel system. A too-rich mixture wastes fuel, pollutes the environment, and can even lead to spark plug fouling and engine misfires. I recommend you check the air filter or oxygen sensor right away, as aging of these components is a frequent cause. Don't delay, or you might damage the catalytic converter, which would be more expensive to repair. Regularly replacing filters and using cleaning additives can help prevent this issue.
I learned this from my DIY repair experience. A long-term fuel trim value of -14.7% is a clear signal indicating excessive fuel supply and a rich air-fuel mixture in the engine. The ECU is continuously reducing fuel injection to compensate, which could be caused by a dirty mass airflow sensor or leaking fuel injectors. I usually start by using an OBD scanner to check for trouble codes and identify the specific sensor issue. For a simpler approach, you can try cleaning the air sensor first to see if there's any change. Ignoring it could lead to a 10-15% increase in fuel consumption, and you might also face fines for exceeding emission standards. This issue is often detected during vehicle inspections, but make sure to disconnect the battery for safety before working on it. Don't skimp on regular maintenance to save a few bucks.
