Yeah, to check the cops just pull them out of the engine and look into the boots. if there is any rust or other corrosion it should be fairly easy to spot. The long spring inside of the boot will have rust on it at the end (since that end will be a little bit exposed to weather and stuff, if that is your problem). When I replaced mine I pulled the cops out and there was a bunch of rust on the end of all the springs. That rust will prevent the full charge from the cop from transmitting to the plug correctly. Replace the boots or replace the entire cop (really the cop should last 100K or more and the springs inside of the boots are what fails first) it is up to you though. Mechanics will tell you they need to replace the entire cop when a lot of the time it is just a rusty boot. Actually though the mechanic may be saving you from spending more money later when the cop does die on you; cheaper to replace the entire thing since they have the cop out of the engine; will save you money on work time if they have to pull the things out later on to replace them. But like I say, the cop itself should last 100K miles or more. If the springs look good then squirt some dielectric into the boots, that will help the full charge from the cop to contact the plug and fire the thing correctly.

 

my truck is now running great! i changed the spark plugs, the drivers side monday after work and the passenger side last nighte after work. i'm not sure but i think a big problem was the buildup on the blade under the cop, i scraped them off and used some contact cleaner on them and put new dielectric grease and with the new plugs it's running like new again2004 fx4 f150 with edge evo k&n filter and flowmaster exhaust sounds and runs great average mpg is now up to 17.5 on the evo

 

Great news...^^^ I knew had to be the plugs/coils....the coils ground at the base so that very well could have been part of it