Howdy all. I'm Josh. New to the forum. I bought an 03 F150 4.6 auto super crew with 201000 on it! It's high, I know but the price was right!

Well, it has it's issues...the biggest is it's only getting 13mpg! I drive like a grandpa..should be better. It also has a rough idle occasionally. Can't find any vacuum leaks....I'm thinking plugs might help. Lord only knows when they were done last. I plan to service everything, plugs, oil, trans, diff...everything.

Any ideas to the cause would be great. Thanks in advance.

 

Not until you find something positive to run with.
Buy a Scanner with the money you saved and look at the live data for an issue waiting to become serious enough to set a code.
Could need Ox sensors, Cats could be restricted etc., should be treated to new plugs, tires may need to be pumped to at least 30 psi, IAC may need cleaning, EGR may be leaking, thermostat may be stuck open etc.
You do know the truck weighs on the order to 5600 lbs +/- with you and a tank of gas aboard!
Good luck.

 

Thankfully, I can keep that extra money in my pocket! My father in law own an automotive shop and we've already had it hooked up to his newer Snapon MODIS machine. Only code it had was a theft code. He said cats looked good. I was going to go and clean the IAC and all that as well. Other than that slight rough idle and the bad MPG's it runs good. Yeah...it's got a little weight on her but she's a good 1500lbs or more less than that suburban I used to have!

 

Clean the MAF and throttle body, too.

 

Oh yeah...I'm not 100% sure on this but I think the fan clutch is either staying engaged or coming in and out rapidly. It's not ever hearing but that added strain when not needed could be a factor as well...I think. I'd like to put an electric fan on it anyhow to free up that power for the engine and maybe save an mpg there if possible.

 

13 isn't horrid. That's what I get and my truck runs perfect I have a couple extra cylinders in there though.

Seriously though - it's a truck, it has 200k, and it's not terribly below average according to other F150's. What kind of mileage did you expect? Check this out...

http://www.fuelly.com/car/ford/f-150/2003

 

At least 16. I had a 01 Sierra with a 5.3 and I averaged 16-17 summer and 15-16 winter. It would get 19 on the highway and I didn't think that would be unreasonable to expect from this...that and the previous owner said it was getting that before the idle issue started so I was hoping to get it back. I've got a civic that once I replace the head gasket will be my gas saver and it won't be that big an issue...but I'd still like what I can get out of it.

 

I would think 16 is possible. I got that with my 5.4. Tune it up. Use Motorcraft plugs torque to 28 FT/LBS.

 

Well, I've replaced one vacuum line that was sucking shut and the plugs yesterday. So far it seems to be running better. I haven't detected the idle issue again yet. Going to fill up today and see if the MPG's change. Should take about a week to find out.

 

Well, still idles a little rough occasionally. MPG's are about one better average per tank it seems. I'm thinking I've got another vacuum leak somewhere...just no clue where. Any common areas to check? Thanks.

 

Coil pack springs may have little corrosion built up. Fuel filter maybe dirty or its the type of gas. Wont hurt to throw some Heet in the tank help remove water. Other kinds people swear by gas additives never had a bottle of it cure a rough idle before I just use a different station til it gets worse enough to throw a code to pin point or clears up.

 

Coil springs are good. I checked them when I did the plugs and it has a new fuel filter too. I'll try the heat. I put good fuel in it but who knows about the previous owner. I'm still leaning towards a vacuum leak.

 

Skip the HEET. HEET is nothing but an alcohol and you're getting plenty of that in the gas you're buying. Use a can of Berrymans B12 instead. Add it to half tank of gas with mixed driving. It will clear any water and clean the injection system too. You may have sticky ring packs. These engines are prone to it. I'd suggest running Delo 400 thru it for 3000 miles and let it clean up the internals. Use a quality filter.