Why does a TEC TD80u have 3 pickups? (CIVIC)

[POS carb]

kind of off topic...
I have a TEC TD80u here on my desk. It has 3 pickup coils in it, I was hoping someone could break down the function of each for me

the top pickup coil faces a rotor with a single lobe on it. I assume this is some kind of top dead center reference

the middle one faces a 24 tooth wheel.

the bottom one faces a four lobe one like the one in the 3gee TD42K, however it does not hook up to the ignitor

the wires all leave the dizzy, I guess to the ecu. Why does it need 3 sensors when 1 can do the job of all 3? If they cut one of the 24 teeth off that could be used as a TDC and a reference sensor eliminating the need for the others

[Hauntd ca3]

it'll be no differant to any other tec dist.
1 for tdc number 1
4 for the cylinder position
24 for crank angle in 15 degree increments

[cygnus x-1]

The single tooth sensor tells the computer which half of the engine cycle the crank is on. It takes two revolutions of the crank to complete a full cycle (fire all four cylinders) so the computer needs to know whether it's on the 1-3 half or the 4-2 half.

The 4 tooth (as I recall) is the TDC marker for each cylinder.

Technically the computer could use just the 1 tooth and 4 tooth signals to control the injector and ignition timing, but the 4 tooth signals are so far apart that the information wouldn't be very accurate. So they add a 24 tooth signal to provide higher timing resolution.


C|

[POS carb]

Cool thanks