Number of cylinders

[stevedarman]

I hope this is an easy one . I wonder why it the ECU need to know how many cylinders KNUMCYLS
as 3x on the crank angle determines when and which coil pack to fire and the 18x will count rpm
also the 3x has 3 different size blades on the rotor so the ecu will know every time no 1 is to fire

[Jayme]

the ecu doesnt know that.... the coilpack knows that... the coilpack just sends the reference pulses to the ecu and the ecu sends back the est pulses. in an 808 the ecu never gets told which cylinder it is. you have to tell the code how many cylinders so it can count out the degrees for spark advance. if it knows that if there is 6 cylinders then 6 pulses = one cycle, then it can use that to calulate the spark. if there is 20 ms between pulses and its a 6cylinder then 20 ms = 120 crank degrees, so it can then calculate how many milliseconds it has to wait to fire the spark so it lands at exactly the right crank degrees. it also uses the cylinders setting in the resistors on the memcal to fire the injectors at the correct intervals. 4cyl = every 2nd ref pulse, 6 cyl = every 3rd, etc.

[charlay86]

Are you talking about OSE12P? It does not support sequential fuel injection so it doesn't care which exact cylinder is firing.
Ecotec (VT+) PCMs do know which cylinder is firing, they have sequential fuel injection.
However you need more than just 3 different blade/window widths as the crank rotates 720° for a complete cycle, which is why they have a sensor on the camshaft too (a pulse from the cam sensor indicates #1 cyl).

[Holden202T]

Ecotec (VT+) PCMs do know which cylinder is firing, they have sequential fuel injection.

Hate to be pedantic but VS was the first ecotec pcm to have sequential.
VT was the first V8 to be sequential.

[VL400]

And the vr v6 auto was the first to know which cyl was firing, has banked injection and individual cyl spark trimming.