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Everythings running fine, but I'm curious about the timing wheel on my 1500. I know there are two pick-ups, so I'm sure there's enough information to generate sparks when needed, but why are there 11 teeth on this thing rather than 12 or 6 or 3 or 24?

Thanks.

Jack
 

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I thought there was always an odd number on timing wheels, the odd number (11) is the break.
 

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Jack Joyce wrote:
Everythings running fine, but I'm curious about the timing wheel on my 1500. I know there are two pick-ups, so I'm sure there's enough information to generate sparks when needed, but why are there 11 teeth on this thing rather than 12 or 6 or 3 or 24?

Thanks.

Jack
Interesting question, I'm embarrassed to say I hadn't given it a thought before. I do know the Electronic Control Unit can vary the spark timing depending on the intake air temperature sensor, coolant temperature sensor and the gear shift position sensor. The static timing of the timing wheel normally is fixed unless a modified wheel is installted. I don't believe the timing pulses directly control the firing of the plugs, they give timing or crankshaft position indication to the electronic control unit which determines the actual firing point of the sparkplug based on the input of the various sensors. At least that's my guess! If it didn't work that way the ignition timing would be fixed and that wouldn't work very well, you need advancing and retarding to get power and good idle.

:waving:
 

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Jack Joyce wrote:
Everythings running fine, but I'm curious about the timing wheel on my 1500. I know there are two pick-ups, so I'm sure there's enough information to generate sparks when needed, but why are there 11 teeth on this thing rather than 12 or 6 or 3 or 24?

Jack, there are all different types of ‘trigger wheels’ depending on the number of cylinders & type of ign electronic module box.. A very popular 4 cylinder trigger wheel set-up is the 12 (–1) trigger wheel (that would contain 11 teeth).. On most 12 (-1) trigger wheels there is a larger tooth spacing just prior to TDC so the electronic module knows where TDC actually is. A 4 tooth trigger wheel with a wide tooth corresponding to TDC could also be used, or even a double tooth at TDC.

As long as the ign module (or ECM) is set up to read what you have, about anything can be used as long as there is a way for it to tell TDC (or additional cam sensor(s) are used to determine TDC).

Usually the more teeth used the better the low RPM resolution of the signal as the signal appears more often, but as the engine RPM increases the more teeth involved the harder the signals are to condition as they appear slurred & hard to distinguish highs & lows..

JDC
 

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BINGO!

Thank you, guys. I gathered that the wheel was just an information source and didn't itself generate an action but only provided information, like exavid said. But I was wondering why a tooth might be "missing", and I think JDC's explanation tells me what I was looking for: That missing tooth hardnails TDC. That also explains englishted's observation that they always have an odd number, at least for engines with even cylinder counts.

Since the wing makes a spark on each revolution and not just the compression stroke, the electronics don't even have to care whether the stroke is compression or exhaust . . .

Thanks guys. Just wanted to know what that was about.

Jack
 
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