Negative means the computer is pulling fuel by reducing the injector flow. It bases fuel trim on the feedback of the AF sensor(s) and the calculated load, as well as where your foot is on the accelerator. The trim value is equivalent to the percentage in relation to the combustion cycle. In other words, the computer is pulling 13+% of its base fuel map for each combustion cycle. That's a lot.
Usually, when the fuel trim is negative, it means the fuel isn't getting burned efficiently within the combustion chamber and the oxygen content is low by the time the gases reach the AF. Remedy is usually a set of plugs, clean the fuel system and check your air filter and PCV valve. Poor quality fuel will also cause it since it doesn't burn effectively.
Are there any codes stored in the ECM?
Usually, when the fuel trim is negative, it means the fuel isn't getting burned efficiently within the combustion chamber and the oxygen content is low by the time the gases reach the AF. Remedy is usually a set of plugs, clean the fuel system and check your air filter and PCV valve. Poor quality fuel will also cause it since it doesn't burn effectively.
Are there any codes stored in the ECM?