the pcm will keep it running in what it thinks is that range
but if there is voltage of say 100 mv added you will only see it for a second or two , then the computer will lean the mixture and bring voltage back into range
only the fuel mix will be lean
Let us know how it works out for you. I still have the one I made, but after experimenting with it for awhile and seeing no positive results I just turned it off and that's the way it's been for since.
The purpose of the EFIE is to add voltage to the signal from the O2 sensor to the computer giving it a "rich" signal, which would allow the computer to lean out the mix. It used one and it did that and I also have the car "test" smoged with the EFIE on and it did run lean. All the numbers improved except the NOX which went through the roof. The numbers were 2-3X normal and if it had been an official test I would have failed. The 14.7:1 is the compromise the EPA has established between mileage and pollution. If you go leaner, then you are adding more O2 in the system, which then combines with the N in the air causing more NOX.