Originally Posted by Arthur Dalton

That is exactly what has happened .. the newer ignition design specs. take the plugs resistance into consideration for spark control from the ECU triggers, but b/c they no longer are making the non-resistors , they throw the resistors/plats at you for the older systems and claim they fit.. well, they fit alright...but we know they don't work too well.
Bottom line..if the original equipment specs call for non-resistor plugs, that is what is needed to get optimum spark/timing/duration for that system.
And if you can't find them in Bosch, get NGKs ..
Don't tax your ignition system, you will be sorry..