Over the last few months my 2004 FX4 has developed a slight "Misfire" while idling. Truck has 160K+ miles and the plugs were changed around 120K miles. The other day I popped the hood and started unplugging COPs while running. Only 3 or 4 of the 8 made it run rough when unplugged. The others I unplugged made no difference which leads me to believe that I have some bad COPs. Can anyone chime in and confirm my suspicions?

 

Can you get any codes pulled? If you have a misfire, you should be able to see that. Go to your local autozone, advance auto, O'Reilly auto parts and get them to pull the codes. There's a bunch of things it could be, but don't guess by disconnecting COPs. When did you do plugs last?

But yeah, go get your codes read.

 

I have a scan tool but there are no codes. The new plugs only have 40K miles on them. They were changed a couple weeks after I bought the truck. The new one piece plugs were installed.

 

We're boots and springs changed when the plugs were done?

 

No they were not.

 

I'd replace them. They're cheap, I think I paid $35 for all 8.

 

I agree, also be sure to use a dab of dielectric grease where the boot meets the plug

 

I removed a couple of the front cops and the boots look fine. I notice that it's worse when the motor is could. There is a slight hesitation when accelerating and then I feel it start to pull harder.