Posted by pat on February 18, 2002 at 18:26:34:
In Reply to: Re: Firing Order:enlightened! posted by Ulf on February 18, 2002 at 14:44:26:
Trouble is, since the sensor is on the crank, it doesn't have any way of knowing which one of the two signals to ignore (per complete firing cycle). If it ignores every other one, there's a 50 % chance it will be the wrong one (for the engine to run). This wasn't a problem with mechanical points which were driven from the *camshaft* (crankshaft makes 2 revs for each camshaft revolution in a 4 stroke - so firing on the correct revolution is easy if you use this as your sensor). But you lose 1 half of the angular resolution (timing accuracy), and the timing is subject to slop in the valvetrain, hense the crankshaft sensor and computer on modern engines.
Good news is, most/many modern electronic tachs take the waste spark into account. Heck, many distributor-less cars use a waste spark between opposing clinder pairs also. So waste sparks are not that uncommon in any modern engine. However explaining and understanding it all is another story (I'm not very good at explinations). -pat