uh60mip

Just looking for some insight from those more experienced with the new engines. I've got an 11 FX4, with the 5.0 V8. I've been using all synthetic oil, which has worked well. My concern is with the plugs. I've got over 85K miles on it, and mileage has finally started dropping. I've seen several different opinions on other forums on which plug. I'm curious as to what plug has the best reputation (aside from E3) for performance, and the best gap most have experienced. I've seen recommendations from 30 to 55, so not all of them can be right. Any help is appreciated.

Koolponycar

.042-44 and stock motorcraft plug

paintballdude05

I'm planing on going with stock plugs and stock gap.

TNrover

I just replaced mine on my 2013 5.0 and used the Motorcraft SP548 plugs. I gapped them at .044. Idles more smoothly now and went up 1-1.5 mpg on the hwy. My old factory plugs were .050-.055. I run a 5-star 87 performance tune.

paintballdude05

What was your odometer at when you changed them?

uh60mip

Thanks for the replies. Based on this and discussions from one of the local techs who drives one himself, I think I am going to go with the 548s and .044 gap. He gets the same mileage I used to get (22-23MPG on a 5.0 FX4). If he drives one of the trucks and has tweaked it for optimum mileage with those plugs, he's got to know a little something more.

RLXXI

Air filter will make more of a difference in fuel economy. If the engine isn't miss firing, the plugs are doing their job. OEM are 100,000 mile plugs.
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paintballdude05

I just pulled all my plugs today, cleaned and gaped them to .045. They looked good for what I assume are factory plugs but they were gaped to around .053. It's probably just in my head, but the truck seems to idle better than before. I'm at around 70k miles so I'll run these until 100k then swap them out.

Spiky

Stock doesn't exist anymore. 548s are replacement for stock with new tips.

uh60mip

Agreed. I use an Airaid dry filter. Used to have a K&N, like I used on other vehicles over the years, but the heat generated by the 5.0's engine caused the oil to evaporate and get on the MAF sensors. Truck thought it was at 10,000 feet. Didn't run for very long. K&N made it good, though, paying for my dealer work to clean and replace. My FX4 is getting ready to hit 90K in about 1500 miles. Love the truck !