Posts Tagged: STFT

Short Term Fuel Trim Diagnostics Guide for Rich Conditions

Professional Diagnostic Strategy to Diagnose and Fix a Negative Short Term Fuel Trim Condition Quick Summary A negative short term fuel trim (STFT) at idle—especially in the –10% to –25% range tells me the engine is running rich, and the PCM is actively pulling fuel to compensate. In my experience, the root cause almost always comes down to excessive fuel entering the engine at low airflow. The most common culprits are: • Leaking fuel injectors • A stuck open EVAP purge valve • High fuel pressure • Or faulty sensor inputs The … Read More