What does a stable long-term fuel trim (LTFT) of -22% suggest about the engine?

A stable long-term fuel trim (LTFT) of -22% indicates that the engine is adjusting the fuel delivery to compensate for a richer condition. In this context, a negative LTFT suggests that the engine control module (ECM) is reducing the amount of fuel being injected into the combustion chamber because the system is detecting an excess amount of fuel present in the exhaust gases. This adjustment aims to bring the air-fuel mixture back to the optimal stoichiometric ratio.

When an engine is running rich, it means there is more fuel in the mixture compared to the amount of air. This condition can arise from various factors such as a faulty fuel injector, a malfunctioning fuel pressure regulator, or other issues that lead to excessive fuel entering the combustion system. The negative LTFT value reflects these compensatory adjustments made by the ECM to avoid performance issues and emissions problems that can occur as a result of running rich.

In summary, a long-term fuel trim reading of -22% is a clear indicator of an engine running rich, leading to adjustments in fuel delivery from the ECM.