First off, great site! Now, my problem. I have a 2010 with the 4.6l 3 valve. It started off with a rough idle. It went to the dealer who cleaned the injectors. The idle was a little better but still not perfect. Here, 6 months later and got a cylinder 3 misfire. I changed the cop and fixed that. Now, if I'm running a steady speed and lightly touch the gas, it starts bucking like it dropped a couple cylinders. Gas mileage has dropped from 16 to 14. The truck has 140k miles. Plugs were changed last summer with stock Motorcraft.

 

Did you make sure the gap was set correctly on the new plugs?

 

Things to check:
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• air filter.
• clean the MAF sensor.
• check for a vacuum leak.

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You may need a new set of COPs.

 

Sorry for the late response but the truck is back to normal for now. All 8 plugs were bad. The gap had opened to around .075 and all appeared to have been burning hot. The plugs had only been in for about 30k miles. The fuel trims don't indicate a lean condition so I'm not sure what caused them to burn up.

 

Congratulations! Thanks for letting us know. That is curious why the plugs failed so soon. It will be interesting to see if the new set lasts.

 

I wish I knew why they went so quick as well. They were stock Motorcraft plugs and the ones they replaced had 120k miles on them. I'm going to keep a close eye on it.