Is a Long-Term Fuel Trim of -14.7 Rich or Lean?
2 Answers
Long-Term Fuel Trim -14.7 indicates a rich condition. Below is additional information: 1. Fuel Standards: Typically, long-term fuel trim parameters range from -23% to 16%. A value of 0 means no fuel compensation is needed to achieve the correct mixture concentration. A positive value indicates the injection system needs to inject additional fuel, suggesting the engine's air-fuel mixture is lean, which usually makes the vehicle hard to start. A negative value means the injection system needs to reduce fuel to correct an overly rich mixture, so a negative long-term fuel trim indicates the vehicle's air-fuel mixture is too rich. 2. Long-Term Fuel Trim Standard: Generally ±5%. Exceeding this standard likely indicates an engine fault. If the vehicle's injectors are clogged, both fuel injection volume and atomization effect will be poor, resulting in a leaner combustible mixture in the engine cylinders.
A long-term fuel trim value of -14.7% is indeed quite interesting. A negative value indicates the ECU is actively reducing fuel, which typically suggests the air-fuel mixture is running rich. Just like the Camry I worked on last month at the shop—it also had a long-term trim of -15%. Upon disassembly, we found a leaking fuel pressure regulator. This negative trim means the oxygen sensor detected excessively rich exhaust, forcing the ECU to reduce injector pulse width as compensation. I recommend focusing on checking whether fuel pressure is too high, if there are any injector leaks, or if the purge solenoid valve is stuck. Sometimes a saturated charcoal canister can also draw in excess fuel vapors. Remember when we repaired that Passat last time? A drifting oxygen sensor also threw similar trouble codes—all these possibilities require systematic diagnosis.
