Injector timing qns.

[Dale Ulan]

> It depends on the injectors, your fuel pressure, and how low you go.
> On GM speed density systems this is compensated for by fudging the
> volumetric efficiency tables....  sorta beat it to fit kinda thing.
> Aftermarket speed density systems are similar, except that they generally
> look up pulse width directly from (RPM,MAP) instead of pretending to
> go through a VE step.  Bottom line: compensation is done in the calibration,
> the algorithms for speed density assume the injectors are linear.

Actually, the GM system includes an injector *offset* which is a
function of battery voltage (injector dead-time), which is added
to the linear flow time. In addition, there is additional
compensation for fuel pump voltage, which affects fuel system
pressure, which is a multiplier factor used to scale the desired
fuel flow. SAE Paper 810449, 'Mathematical Model of a Throttle
Body Fuel Injection System' by Robert Esperti is a particularly
good paper on this (although it gets mathematical). If you are
into reading papers, 810494 and 810495 are pretty good, as well.
Paper 790742, by G Czadzeck and R Reid of Ford, is a very good and
readable paper on the Ford CFI 5.0L 1980 cars. It covers most of
the 'twiddle factors' required to get the vehicle running properly.
Also, paper 800164 on the GM TBI system is nice easy reading. Neither
of these last two papers have any amount of hard math in them.

The papers I mentioned are early ones because most later papers are
virtually unreadable due to wall-to-wall mathematics. Even the
'Mathematical Model...' is semi-readable. The author discusses most
of the characteristics of injectors.

-Dale