General theory on EFI

[Andy Laurence]

OK, I have been to the site, and have lurked here for a week.  I am very 
interested in the PC based EFI system, as is a friend of mine.  However, I 
am still unsure about how exactly it all works.  From what I can see, you 
can gain inputs from the throttle pedal, air mass sensor, manifold pressure, 
temperature, barometric pressure, crank/cam position, and oxygen content in 
the exhaust amongst others which I have not yet thought of.  The only 
variables in output I can see are the injector timing, and ignition timing.  
The injectors use a pulse width which would be of a set length depending on 
the outcome of an algorithm using some or all of the above inputs, and can 
either be set off at a time relative to the engine position (eg 10BTDC) or 
at a set time (ie. static time gap between them).  The ignition has to 
happen at a time relative to engine position (eg 10BTDC).

Am I missing something here, or is it really that simple?  Also, how do I 
get close to the sort of injector width I want at a certain time?  How 
should I go about developing an algorithm?  Are there any good sites I can 
visit which will explain to me (in intricate detail - I like that kind of 
thing) how to get in the ball park of fuel requirements as I have no wish to 
blow more than a couple of engines playing with this (Fords, and Austins are 
2 a penny here, but getting rid of them is more tricky).

Thanks in advance for any help you can give me, I think I got everything in 
there.

Andy
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