Originally Posted by AlvinByars

xfuego,

As much as it pains me to do so, I have to agree with Bullseye on this one. You are assuming that the two chips (the ECU and the piggyback) are sharing inputs and outputs. That is not the way a piggyback chip works. Normally, the ECU receives its inputs from a number of engine and other sensors, processes the inputs based on tabled values stored within the ECU, and then outputs to various engine/transmission controls. A piggyback chip fits inline between the various sensors and the input to the ECU ... the piggyback receives inputs from the sensors, modifies the inputs, and then outputs to the ECU. The ECU then processes the modified inputs from the piggyback, and using the the original tabled values, sends modified outputs to the various engine/transmission controls. There is no sharing of inputs and outputs between the two chips. Piggyback chips do work, and since the modified piggyback outputs are within the normal range of engine sensor outputs, they are completely safe and cannot damage the ECU. Despite his crassness, Bullseye knows what he is talking about on this one.