i change every 30.000 but they can still look good on outside and weak
in the middle..another way look at plug wires is look at them when dark
outside see if you see any sparking going on..good luck....

When I am wondering, I start the engine at night in the dark and take a
spray mist bottle of water and spray the wires and cap with it.  If I
get a fireworks display, I replace them....

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:  Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

or you should spray gas on um then you'll see if they need replaced
talking about wires..and not good idea on spraying the cap as it could
crack..

  NO. Most of the time you will not be able to tell by looking. Just
replace them at the recomended interval and you will not have any problems.
I would also recomend using factory tune up parts as they last the longest.
Most aftermarket tune up parts are junk.