Does a negative short-term fuel trim indicate a lean or rich condition?

1 Answers
Marie
07/29/25 1:24pm
Excessively rich or lean conditions are detrimental to normal vehicle operation. Here are the relevant explanations: 1. Fuel too rich: Generally, long-term fuel trim parameters range from -23% to 16%. A value of 0 indicates no fuel compensation is needed to achieve the correct mixture concentration. A positive value means the injection system needs to inject additional fuel, indicating the engine's air-fuel mixture is lean (typically making ignition difficult). A negative value indicates the injection system needs to reduce fuel delivery to correct an overly rich mixture condition. Therefore, when long-term fuel trim shows a negative value, it signifies the vehicle has a rich mixture problem. 2. Injector clogging: If a vehicle's fuel injectors become clogged, both fuel delivery quantity and atomization effect will be poor, resulting in an excessively lean combustible mixture in the engine cylinders.
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