Shutting fuel off whie driving.

Roger Heflin rah at horizon.hit.net
Wed Mar 31 18:13:38 GMT 1999



On Wed, 31 Mar 1999, Frederic Breitwieser wrote:

> > As an "electronocally challeged" participant,
> 
> Being a non-electronically challenged participant, I will add...
> 
> > I'd use a resistor and an led connected to the
> > injector harness.  Not sure of the exact value.
> 
> A generic Radioshack LED with a 1K ohm resistor in series would
> display light when the injector is fired, however even at idle, it
> would be difficult to see it going on and off.  Lets see why.
> 
> Assume a V8.
> On true sequential injection, one injector pulse per intake stroke,
> would result in 50 injector pulses per rotation at an idle of 800
> RPM.  800 rpm / 8 cyls = 100, 100 / 2 (four stroke) = 50.
> 
The intensity would vary, but I don't think that could be detected
either.


> At 800 RPM, the led would pulse at or about 50 hz, which your eye
> really cannot see, and would view as constant illumination.
> Flourescent lights actually flicker on and off 60 times a second, and
> the light appears constant to most people, thus illustrating my point.
>

I am not sure they actually go completely off, the phospor may last
long enough to hide the fact.  To convince me someone would need to
point a camara runing at over 120 fps and actually see if being off,
my guess is it would just be dimmer during the off region, since if it
were going off it should have weird strobe affects with most computer
monitors.

> 
> If you have constant LED activity while accellerating, 
> > but none during coast-down, you have your answer..
> 
> Often on deceleration, the injector just misses certain cycles, and is
> not closed off entirely, therefore the LED would still be on more
> often than not.
> 
> And oscilloscope would help :)
> 
A true RMS voltmeter may be able to tell.  You should be able to get
some idea of the duty cycle by the true rms voltage (a voltmeter that
integrates over time, as opposed to the cheaper kind that just
multiplies the max voltage by a fudge factor when in AC mode).  On
decel the voltage should be really low.  With a simple integrating
circuit/lag filter you should also be able to get some idea with a
non true rms voltmeter.   Wasn't someone going to do a pic circuit to
display pulsewidths?   

Additional question:

pics are simple enough that if I already had alot of electronics
knowledge that the advanced book would be enough for me to work with
one?  Is there anyplace on internet that has the datasheets for pics?
I really believe that I probably have enough electronics that the
datasheets will be enought for me.

			Roger




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