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Rising or falling edge trigger

Practical Standalone Tuning

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Hi first time tuner her,

I'm trying to tune a small 180cc motorcycle engin with a microsquirt II ecu, without any coil driver's, the coil is still running through the CDI unit and the factory magneto reluctor pick up, and I have no clue if I should set the ecu input to rising or falling edge?

hello it should be on falling edge

Hi thanks, sorry forgot to ask if you could explain why, so I know for future reference please

It is impossible to say what edge you should use without seeing an oscilloscope capture of the waveform. Reluctor circuits can be designed to work either way up so without knowing which way the factory system was designed for you cant guess, you need to measure.

A practical test you may be able to do however would be to lock the timing in the ecu then rev the engine to confirm that timing (checked with a strobe) is stable over varying RPM, typically if you are using the wrong edge you will see a large timing drift with RPM.

A couple of example waveforms below. You need to look at the trace where is crosses zero volts, the first pic shows the trace is falling as it crosses zero, so this would require a falling edge setting in the ecu. The second pic would require a rising edge.

Falling edge:

Rising Edge:

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