Sorry man but that is simply not true. It can only tell that the piston is at top dead center not what stroke the engine is on. Please think about it for a moment. Every time the engine starts the ECM has to determine what stroke it is on before it fire the ignition. Now if the crank doesn't slow during starting as the piston comes up on the compression stroke why do compression releases exist?

 

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Yes!!! Now we are getting some where. The signal is crank speed and knowing where top dead center is, The crank slows on the the compression stroke which tells the ECM that it is time to fire the ignition.

Remember there are 720 degrees in a cycle but only 360 in a revolution. Come to grips with this and you will begin to understand.

 

Electric motors (the starter) draw more current (amperage) when there is high mechanical resistance on the motor (compression). High amp draw = high heat, which can cause premature motor failure, damage to wiring and increases resistance in the circuit. Compression releases also help those with kick starters a chance to get the engine spun over without breaking an ankle.

When the engine is at TDC it can be one of two strokes, compression or exhaust. Not too hard to design a circle with a mark of some sort at TDC compression for one cylinder. Logic dictates that the firing interval for every other cylinder will be at a predetermined interval based on the angle of the crank throws. xFreebirdx also brings up a good point- it is impossible for a sequential fuel injection system to function without knowledge of which cylinder is on which stroke. ECM sees the engine is on the intake stroke, commands the injector to open (varies the pulse width based on TPS and MAP of course) and everything is dandy. I'm ASE A1 and T2 certified if you have any more questions pertaining to gasoline or diesel engines




Here's an experiment: remove both spark plugs so there is no compression resistance on the engine or starter. Make sure they're grounded against the engine. Try to start the bike. The plugs will fire despite the fact there is no "slowing of the crank".

 

Yes!! Again now we are getting somewhere.

However with the current setup that H-D uses in your experiment the plugs will not fire because the crank speed does not slow so the ECM will not fire the plugs....remember to remove both plugs.

Gentlemen I believe we have a break through.

 

Whoever told you this ridiculous theory of operation must be able to sell ice to an Eskimo. Try my idea before denouncing it, worst that could happen is nothing. Regardless of waste spark or being individually fired, they will fire. Try it on your car, lawnmower, snowmobile, whatever. With the exception of a points system, there is no ignition trigger that is based off of a physical change, everything is electronic. Its either a Hall Effect, AC Magnetic, or an Optical system (Remember the LT1 Optispark system don't ya?) End of story.

 

But we are not talking cars, lawnmowers or snowmobiles we are talking about the current generation of Harleys. Please do try it and see for yourself before you assume the out come.

 

The operating principle is the same. Your theory would be plausible if it was a single cylinder engine, however in a multiple cylinder engine the crank slows down twice (or more). Now the ECM is really confused isnt it? See why it doesnt make sense?

 

No because it knows where TDC is. And if it were my theory then I would be a lot richer than I am. Really try your plug experiment on a 2011 48 like the OP's bike and you will see the neat solution that the folks at H-D came up with. Really go try it and see for yourself...it's what you keep telling me to do.

I'm not trying to make enemies nor trying to make anyone think I'm smarter than anyone else, I am not, just trying to explain the answer to the OPs question.

 

I've already wasted enough of my time here. BTW- according to what's been said, it won't apply to my bike since it has a carb on it. No ECM = no variable speed ignition position concept.