That's the thing, you never need to ground it to the case if it has the supplied grounded boot on it. If you take the grounded boot off then it's up to you to ground the braided cable to the engine case and the same when testing plugs. If you are removing this you should have some idea what you're doing. The manual says nothing about it, but everyone knows this.

I agree with Jezmo. But, I only have what I've read here. They also say never to power up an ignition without the sensor connected. Been there, done that, nothing happened.