dc42:
PS - is the sensor itself well away from the HT leads and ignition coil?If all else fails you could try a R-C filter on the input pin. Something like 1K between the pullup/hall sensor and and the pin, and 10nF or 100nF from the pin to signal ground. But this should not be necessary if your sensor uses shielded wire and is correctly grounded
I don't have any pictures of the setup but I can tell you that I did exactly as you said with the shielding, I grounded the shield (tied to the hall effect ground) to the UNO. I'm using a 4 conductor shielded wire and power and signal are protected by the shield. I kept the bare wires short (less than 1")
For now the hall effect is the only thing close to the bike, the crank position wheel (where the hall effect is) is about 12" below any HT wires. The shielded wiring is running along the floor, 5' away to the uno and computer resting on my tractor (lol), The uno is powered by the computer. There is no power being shared from the bike. The signal wire is 12" or more from any HT wiring.
There is a problem inherent with wiring on a bike... sooner or later I will have to route the signal wiring to the dash area... which will pass by the coils and HT wiring within an 1"... 