This is going to be a problem isn't it?

[BottleFed70]

MSII,v3 PCB, 2.36 firmware, MT2.25



I currently have my ignition input capture set to "Falling Edge" as I found I would get RPM spikes/dropouts if set to rising edge. This worked fine for fuel only, but I'm guessing that this is going to be a problem when doing ignition control.

Car is a 1970 mustang with 351W V8. For ignition control I'm using the stock points distributor that's had the points swapped out for a pertronix unit. The output from the pertronix is now fed into the MSII(used to go to coil like points) with the help of a pullup resistor.

The pertronix was designed so that the spark happens on the rising edge just like the old points system. Am i correct in thinking that the pertronix unit would introduce some amount of dwell and that triggering off the falling edge would then introduce some error in my input timing which would in turn effect the output timing? And that this error will manifest itself as different amounts of trigger offset at different engine RPM?

[woh]

what is important is that falling edge of the IRQ (output of U4) will be where the spark happens. When that goes down (5V to 0V) that is the Trigger Angle at the crank. From your description you have it wired so a rising output at the distributor will give a falling IRQ. This way the distributor is in its normal location.

You can wire the distributor to give a falling IRQ when there is a falling output from the distributor. This will however change the syncronization of the High Voltage rotor to the High voltage output. Best you fix any glitches you have.

If you use the MS to provide the spark, the dwell will be determined by MS.