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fyi, your computer (ecu, dme) does two jobs - trigger the spark plugs (timing) and trigger the fuel injectors (fueling). internal combustion works best with a ratio of air to fuel (afr) of 14:1 (stoichiometric). the computer uses the mass airflow sensor (maf, a hot wire that changes resistance with airflow) to determine how much air is entering the engine (which is controlled by the throttle body - a butterfly valve connected to your gas pedal) and then calculates how much fuel to provide based on programmed tables called maps. under low load your computer tries to maintain an afr of 14:1 for best efficiency. the oxygen (o2) sensors on your exhaust can determine if you are at 14:1 or not; it is a narrow band o2 sensor that puts out a large signal when the exhaust gasses indicate a 14:1 mixture, and a very small signal if the mixture is lower than this (rich - more gas than needed) or higher than this (lean - less gas than needed). if the o2 sensor thinks things are off then the computer modifies the maps (‘trims’ them) to bring things back to 14:1. at higher load/rpm, the engine should run a little rich (ie, as per jaay, 11.2:1). this is because the additional gas helps cool the pistons and valves in high output situations. a rich situation is much better than a lean situation where everything burns much hotter with the excess of o2 and holes get burnt in pistons, etc. when your car gets in a high load situation and wants to run a rich afr, however, the o2 sensors are of no help as they are narrow band and out of their operating range. in this case the computer just uses the maf signal and the programmed maps to set fuel levels (this is called open loop operation).
with forced induction (fi - turbo, supercharger) you can push the maf out of its operating range, or push the ecu into an operating area for which it has no maps. further, the additional power developed by fi requires richer operation to provide additional cooling. to address this you can reprogram the ecu as per iA, add a 7th injector as per tpc (a seventh fuel injector mounted in the intake manifold tied to an rpm switch that triggers additional fuel when a certain rpm is exceeded) or go wide-band.
a wide band o2 sensor has a much larger operating range than a narrow band o2 sensor and can return a proportional signal through all potential afrs. with one of these connected to a piggyback computer you can do real time (closed loop) fuel management all the time and not just at low load stoichiometric. a piggyback computer is a device that intercepts the maf signal (and rpm signal, and other inputs such as intake air temperature depending on the model) and sends the main computer a modified signal designed to maintain whatever afr you program into it ... which means you have to program it ...
so, your call. get a $1000 tune from giac or softronic, or buy $750 worth of sensors and computers and a whole bunch of dyno time to diy.
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