TRIG­GER WHEEL

Classic Ford - - CFTECH -

The whole sys­tem needs a ref­er­ence so that the ECU knows whereTop Dead Cen­tre (TDC) is and there­fore, when to trig­ger the spark’s cur­rent. There are two main types of trig­ger wheel — shown is an af­ter­mar­ket sys­tem, which will con­vert any non-fuel in­jected en­gine; such as a Cross­flow or early Pinto, al­low­ing it to be bolted to the front pul­ley wheel with a bracket for the pick-up.

It works by hav­ing one tooth for ev­ery 10 de­grees of crank ro­ta­tion, which the pick-up sen­sor counts.The 36th tooth is miss­ing so the ECU then has a ref­er­ence and knows when to start its cy­cle. Some en­gines — Zetecs for ex­am­ple — al­ready have a trig­ger wheel built into the fly­wheel, with a pick-up mounted in the back of the block.

Some ig­ni­tion sys­tems still use the dis­trib­u­tor as the means for dis­tribut­ing the spark although that’s its sole role and it’s empty of points or elec­tronic ig­ni­tion.

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