So, about two weeks ago I changed the oil, checked tire pressure and replaced the PCV valve in my truck. Oil wasn't absurdly old, it was about 2000 miles and 4 months. Tire pressure was around 22psi per tire, took it up to 32. Makes sense it was low... I mostly ride the bike and leave the truck alone, and the temps dropped about 25 degrees recently here in AZ.
I was complaining about the transmission in this truck about a month ago here, and I know this has nothing to do with the transmission at this point, but fuel economy went from about 15.7 highway to 18.1 highway. Just from those three things in the last 2 weeks.
I have a hard time believing that tire pressure accounts for 1.4mpg, or nearly 10% improvement. Maybe on a sedan that gets around 25mpg or more. So I figure I got maybe 0.5mpg from the tire pressure, max.
Can the PCV valve cause that much of a loss in fuel economy? My understanding of how it functions is it grabs unburnt vapor from under the cylinder head cover and channels it back into the air intake. The old one didn't seem to be too dysfunctional... supposedly the check for these things is to shake them. If they rattle, the valve still works.