varnco

V8 5.0. at 100K miles, I changed the air filter and spark plugs. Results (unscientific). I changed the air filter first, then spark plugs.

I ran the truck at 69MPH, full tank of gas, for a short, 5 mile drive, the same drive each time, truck always full of gas. I gapped the plugs at .49, using the new motorcraft recommended (since they discontinued the original ones)

Before: 18.5MPG at 69MPH
After Air Filter: 19.2MPG at 69MPH
After Spark Plugs: 17.5MPG at 69MPH
After 1 tank of Gas (500 miles): 19.7MPG at 69MPH

My truck used to have the "tick" that is common - it ticks no more.

FWIW.