What is the long-term fuel trim value?
2 Answers
Long-term fuel trim values between -25% and 25% are considered normal. Additional information about long-term fuel trim values is as follows: 1. If the long-term fuel trim value exceeds 5%, it indicates a fault in the engine system. 2. If it's significantly below 0% (a negative value), it indicates the system is running too rich, and fuel supply should be reduced (by decreasing injector pulse width). 3. If it's significantly above 0% (a positive value), it indicates a lean condition, and the PCM will compensate by increasing fuel quantity (increasing injector pulse width). 4. Since long-term fuel trim tends to follow short-term fuel trim, negative values caused by idle purge are not considered abnormal. The PCM controls the maximum allowable long-term fuel trim value between -23% and 16%. The maximum allowable fuel trim value indicates whether the system is running too rich or too lean.
Long-term fuel trim is a value that represents the vehicle's computer system automatically adjusting the fuel injection quantity to optimize engine combustion, typically expressed as a percentage with a normal range between -10% and +10%. If the value is positive, such as +5%, it indicates the computer is increasing fuel injection to compensate for excessive air, possibly due to a dirty air filter or an air leak. If the value is negative, such as -8%, it means the computer is reducing fuel injection to address fuel line blockage or excessive fuel supply. Having worked on many vehicles, I've found that ignoring this value can lead to a sharp increase in fuel consumption and engine malfunctions. Therefore, I recommend checking it with an OBD scanner every six months. Addressing issues promptly can extend engine life and save costs. Additionally, maintaining airtight intake ducts and regularly replacing the air filter can prevent most abnormalities. If you're unfamiliar with the process, visiting a professional repair shop for a quick diagnostic check is a simple solution.
