The cap/ braiding must be grounded to the engine or you will get interference. That's the ground for the module. A buddy took the ring off the cap where it's an interference fit on the base of the plug and got all kind of glitches. I soldered a wire to the braid and grounded it to the motor. No more interference. Just for a test, put an aligator clip jumper wire from the braid to the motor and see what you get.