factory plugs should last about 100,000 miles, thats when they call for the fist tune up. my last new truck i swapped them out at 70,000 ish, just because it seemed like a good idea. they still looked good.
i took gregbadass to pick up a car he bought, a 98 gtp, it had like 80,000 on it, all original plugs and wires, i test drove it 3 days before he came in to buy it and it ran fine, 3 days later it was misfiring all over the place, we did a quick tune up, and the car was like new again.
so they say 100,000 but they could last less then then that. as greg and i saw 1 st hand.
