Commented hacks of the GM programs have been publicly available for several
years. One of the most vererable $8D copies is on the site of the late 'ECMGuy':
GM only makes reading their programs complicated in order to limit those who
actually understand how the computer works to the technically literate
There is no need then to derive the pw equation - the calculation is there in
black-letter code. Rather than belabor it, the highlights are these:
Generally, GM treats a high-impedence injector as a fixed-weight device,
although in fact it's a fixed-volume flow controller. GM uses voltage & low-pw
compensation (offset) tables to correct injector opening-time latency, trying to
achieve linearity for their equation.
Based then on some nominal fuel density, the (compensated) pw for the injectors is
calculated to give a stoichiometric weight balance of air to fuel. Stoich is generally
taken as 14.7:1, though it is adjustable in the code (within small limits). It's also
worth noting GM allows for different stoich ratios at idle and under load, just to make
tuning the engines that much more elegant.
BTW, the GM code also contains the complete definition of the ALDL output stream.
Thus the tuning & scanner info needed to work with these ECMs is already de facto
public-domained - which is not surprising for a near-20 year old computer system.
edit for typo
[Modified by DOCTOR J, 3:53 PM 11/11/2003]