Spark-in issues

[GrahamB]

I've been having problems with sporadic loss of rpm data on my TZ250. One run it will be fine, the next not... or it will come in or go out halfway through.

At present the input is connected to the primary of the upper coil, as is the tacho. Looking at the source on a CRO with the engine running, the ECU sends a 12V square wave pulse, about 1.5ms duration. Rise time looks to be about 100ns, so dV/dt is around 100 times the 1kV/s threshold.

However, at the tail of the pulse there is about 1ms of ringing due to the coil inductance, at somewhere around 20-50kHz, about 12V magnitude (ie 24V p-p). I'm wondering if this is the problem?

Any thoughts on whether using a snubber diode across the coil primary would be an effective way of dealing with this?

[RTUSA]

Graham:

Question is with Hardware Support.

[GrahamB]

Thanks.

I tried the snubber idea... and realised it was dumb. The spark is triggered by shutting the current OFF... so the diode kills the spark. Oops