I realize that I am coming to this party late but wanted to throw my experiences with spark plugs into the mix just in case someone looks at this thread for information on a spark plug related problem. I have a 94 Mercedes 500SL that will not run on any kind of platinum plug. The only thing I can put into it that it will run on is the cheapest Champion plug available. Granted I need to change them about every 30.000 but if I screw any other plug into it, it will start running bad in less than a week. My wife had a 97 Infiinity Q45 that would reject anything but the factory recommended NGK's at $29.00 each. Anything else and the engine would start misfiring somewhere short of 12.000 miles while the NGK's would easily go 70,000 plus. Years ago I had a friend with an MG TC. That car misfired to the point of being undriveable on Champion plugs, but would run fine on ANYTHING else. I grew up in my dads auto repair shop and worked on them until my late 30's when I decided to try constructon. I have had my fingers wrapped around a wrench for over 60 years off and on and I have no logical explanation for any of this. But the point is that the internal combustion engine can be a finicky beast at best. So if it does not like the plugs you have in it try another brand, it might work. One other thing that just danced across my brain, for those of you old enough to remember Ak Miller. He had a shop foreman, who's name I do not remember, that ran a corvette at Bonneville. He once made a record run in that car with 8 different brand name plugs in it, go figure.