If my plugs read no resistance, open resistance, or anything but 0.6 ohms, I replace them. And, I replace all of them at the same time. The $50 is less than a tune up on a gasser, as with a gasser I also replace the dist cap and rotor.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D