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Short term fuel trim


The short term fuel trim is used only in closed loop in modify the fuel delivery to the engine in order to keep the air/fuel ratio close to stoichiometric, which is the optimum air/fuel ratio for catalytic converter operation. Normally short term fuel trim should be within the range of -10% to +10%, otherwise the fuel maps need to be tuned at part throttle.


Note that the short term fuel trim will often go very high during fuel overrun conditions while shifting.