Newbie question about ECU

[Lil bastard]

Not the case. You're expecting too much from the computer - DME.

The DME receives signals from the various sensors. It then compares these to maps in the software in sort of a "if you see this... do that" way (overly simplistic, but that's the essence of it).

The OEM software writers, when producing these maps, include only the possibilities expected with the OEM gear. This is because the file size is limited, and much aftermarket gear is an unknown to them since much of it is produced after the software is written or the car released.

If the DME gets a series of signals with values outside these pre-written maps, it cannot find instructions in the software on how to proceed - it gets confused.

But, to deal with this confusion, another part of the software tells it, if you see anything other than these pre-set, defined values, use this default fault map. This fault map usually consists of the safest, least damaging (and therefore performance inhibiting) fuel and spark settings and assumes that if any signals are outside the program parameters, that some engine part, or it's sensor is damaged. So it goes to it's default map to lessen or prevent any additional damage. It may then also throw a MIL (Malfuction Indicator Light) or CEL (Check Engine Light).

There are also limits in the software to minimize wear to the engine, such as rev limits, etc. Also, the OEM software MUST work to produce mandated Emissions results. A lot of aftermarket gear is really only legal for Off-Road use (though many Mfrs. minimize awareness of this in their advertising), and so has no such requirement.

Aftermarket parts such as Intakes or Exhausts usually need different Fuel and Air quantities, or different Spark curves and durations than the original software contains in order to produce the added performance.

So, to accomplish this, different maps are loaded into the software (sometimes the original software maps are altered, but this is a less desirable way to do it).

That's why re-programming or re-chipping is necessary.