Fuel trim is being discussed. Technician A says a + 12.0 percent LTFT value indicates that the system is running 12 percent richer than normal. Technician B says LTFT should constantly change between positive and negative values when the system is running in closed loop. Who is correct?

Question

Quizplus · Accepted Answer

A +12.0 percent LTFT (Long Term Fuel Trim) value indicates that the system is adding 12 percent more fuel to compensate for a perceived lean condition, not that it is running richer. LTFT values should stabilize and not constantly change between positive and negative when the system is running correctly in closed loop; constant fluctuation indicates a problem.

Fuel Trim Is Being Discussed