At 10:22 PM 7/26/2011, Rocket J Squirrel wrote: >>The normal idle stab on the 1.9l engines is an electronic module that >>advances ignition timing when idle falls below 750 (Federal) or 850 >>(California) rpm. > >But how does it know? Where's the clock -- timer -- in that module? It gets rpm info from the Hall sender. I haven't had one apart but clearly there's an oscillator or counter that the Hall signal is compared to. As long as it's faster than the internal oscillator it gets passed straight through to the output. If it becomes slower, the circuit advances the phase of the output, advancing more as the input continues to slow. Obviously it has to compare at least two Hall pulses and can (I believe) at the earliest advance the third and subsequent ones. It does react pretty fast; if you put a timing light on it you can see the timing jumping around rapidly. Yours, David |
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