FW: Processor selection for datalogger

[Jonathan R. Lusky]

Roberto L. Landrau writes:
> 
> Does anyone have a feel for what the injector PW signal looks like
> (timing)?  I suspect it is a pulse between 1-10msec wide at idle.
> The technical service manual for my car describes the sequence and the
> crank angle at which the injection takes place, but it doesn't tell
> you how wide the pulses are.
 
With latemodel GM (Rochester, i think) injectors (the ball type with
the director plate) you can go down a little bit below 1ms if youve
got a really good controller.  I think most people like to stay above
2ms.

> My specific question is: how wide is the injector pulse signal?  How
> often do I need to sample to get a reasonable reading (i.e. is it
> 5msec +/- 0.000001msec, needing a 1e6 counter, or is it 1-100msec,
> etc.)?  I realize this varies from car to car, but I am only looking
> for an ``order of magnitude'' starting point.

An injector fires once every two engine revolutions.   It needs
at least 1ms offtime between firing.  Maximum dutycycle is about 90%
I believe.  So your frequency is a function of RPM, then you apply
both of the above rules to figure out what your maximum pulse width
could be.

-- 
Jonathan R. Lusky                       lusky at knuth.mtsu.edu
http://www.edge.net/erc/lusky.html      (615) 455-9915
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68 Camaro Convertible - 350 / TH350 \_/ 80 Toyota Celica - 20R / 5spd