I looked at the tuneup specs on my wife's car the other day. It's a 1997
2-door suzuki speck. To set the timing you jumper a couple of pins on the
diagnostic connector, which is supposed to fix the timing, and then set
the timing to 5degBTDC the conventional way with a timing light and
rotating the distributor body.

The distributor has eccentric bumps(same number as there are cylinders)
and a pickup, plus the usual rotor. So it doesn't get a hundred pulses per
revolution like my other car.

There's no vacuum or centrifugal advance on this car, so it got me
thinking how they do the advance, and how I'd do it given the hardware
involved.

Car electronics, to be respectable, always has to have 2 modes, normal
operation and "limp home".

So I'd have the distributor pulses at a failsafe timing, like the 5
degBTDC setting this car is spec'ed at. Then I'd predict the position in
order to do advance. If the distributor pulse came before my prediction,
I'd fire at the distributor pulse. That way if I lost my ability to
predict I'd still get a safe timing and the car would still start and run.

There are some drawbacks to this predictive method, since the engine speed
varies considerably through each revolution. Having just one pulse per
cylinder, it would be more accurate to set the base timing at the maximum
advance, and fire based on a short adjustable delay. But that ruins the
ability to do "limp-home" mode.

Does anyone know how it's really done?

BTW, this car has no crank sensor or TDC sensor. It is real basic for a
1997 model.

Thanks,

Bob

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