I just tuned up my 93Z when I notice dthat the plug on driver side against firewall looked like it had never fired. all other plugs were a rusty red color due to additives except that one plug. the car seems to run the same though, could there be a faulty plug? I pulled that wire off the opti and saw a ark, but the car didin't seem to miss a beat. what up with that?I checked the injector with a stethascope and heard it ticking away. Could it tick even tjhough there is no gas going threw? any next tests thanks!!