runner1

I have a 2007 F-150 Lariat super cab 5.4 liter that I bought new. At 125000 miles I started getting the famous 50mph in/out of OD shudder. After finding this forum and doing some searches, I figure I have the typical COP problem. Took the truck to the dealer (I freely admit I am no mechanic) after checking the truck they call and tell me I need two coils, #s 5 & 7, and new plugs (still had original plugs) and a fuel injection flush. That was what I was expecting and say go ahead. A day and almost a $1000 later I get the truck back and go on my normal, mostly highway 150 mile circuit. This is where the problem starts. I typically get about 16.5 to 16.8 mpg on the highway, about 14 in mostly city driving. After my thousand dollar tune up, the computer shows 13.3 on the highway. I am thinking my computer is off. I check it by mileage and gas used and it comes to just under 13 mpg overall. Next day truck goes back to dealer. Service tech that does the write up tells me that there is nothing they can do for mileage issues, the computer does all the tuning and the truck is fine. I tell him it has dropped over 3 mpg after you guys fixed it. Something is not right, I am leaving it, call me when it is ready to go. Next day I have a phone message the truck is ready. When I get to the service desk the rep tells me that one of the mechanics drove it for 150 miles over the time they had it, runs fine, checks out on computer, nothing more they can do. They tell me they made no adjustments to the truck at all. I take the truck on the same 150 mile circuit I drive every week, this time I get just over 19 mpg driving the same route that I got 13.3 on two days earlier.
Now either I'm crazy (possible), the truck fixed itself, or they screwed up something in the tune up, found it when I returned the truck, didn't want to admit their error, and lied to me when they said they made no adjustments. I'm voting for #3, but I would like to hear what the experts here think could have caused such a drastic change in the mileage.
I should add the 50mph shudder was corrected with the initial tune up. When I drove it and got the 13.3 mpg the only think I noticed was it seemed to hold in gear longer before upshifting under acceleration. It did shift into OD on the highway and turned about 2000 rpm at 70 mph which is normal for my truck.
Sorry for the long post, just trying to figure out what went on.

Ford Fan#1

did you change all of the plugs? And what type did you use? Along with coil packs?

snowborderus

Possible that the first drive after the tune up was the truck "retuning" itself? Once it was driven for a couple hundred miles it got all done fine tuning everything and is "back to normal"? Just a thought.

runner1

The dealership did the tune up. All the plugs were changed. I assume Ford factory parts were used.

Ford Fan#1

oh. Then yeah.. Maybe the computer needs reset

lewissa81

I agree with snowboarderus. To change the plugs, the battery has to be disconnected and the pcm removed. Once the battery is reconnected, the pcm has to relearn all the parameters it uses to adjust fuel trims and whatnot. That can take a while. Keep an eye on it. If your mpg's go down again, you'll know something is up. My bet is that it won't though.

dom07

You didnt get screwed, they just drove it through a relearn cycle.

runner1

I appreciate everyone's responses. The truck continues to run normal, I had no idea the computer had to "teach" itself after the tune-up. Seems like the tech would have told me that when I took it back complaining about the mileage.

Anyway, after reading several posts on this forum, it seems nobody has a "stock" truck. I like mine and it still looks good. I figure its time to improve it. In order, what are the two or three mods I should do to increase its performance without hurting its mileage. The engine is the 5.4

I was thinking things like, air intake, exhaust, chips (I know nothing about those)
etc.

thanks in advance for your thoughts.

FrozenTundraGuy

Forget the chip, get a programmer instead. Also it appears the air intakes are not really worth the money-but you do get a lot more engine noise. Exhaust would help, but don't waste your money on headers-this engine doesn't respond well to them. A good free-flowing exhaust system is your best bet on the exhaust.

Race Sage

Another explanation: I had noticed my truck had gotten significantly improved gas mileage the longer I owned it. Had gone up at least 4mpg and sometimes as much as 6mpg. I had been putting off the "tune up", but it was running pretty rough, so I went ahead and did it myself. My mileage instantly dropped back down. I asked my mechanic WTH? He gave me an excellent explanation. As the plugs deteriorated, the unburned fuel in the exhaust caused the computer to lean the engine out in an attempt to hit target O2 levels, thus the mileage had gone up. With the tune up and everything working properly, the mileage went down, as the computer richened the mixture back to normal levels. The plug evidence (and cap, older truck) would support this theory as I suspect one cylinder wasn't firing at all, and two others were questionable.