Electronic Fuel Injection (EFI) is all the rage today and rightfully so. EFI has many advantages that allow us to dial in the fuel in a dramatically more precise fashion than was ever possible with a carburetor. One of the tools at our disposal is the closed loop algorithm where the target air/fuel ratio commanded in the ECU is compared to the actual air/fuel ratio read by the O2 sensor. If the two do not match, the ECU makes small changes by either adding or subtracting from the commanded fuel in the fuel table to equalize the two.