Just sold my 97 swb reg.cab 2WD with the 5.9..It had 162,000 miles and I was getting 15 miles to the gallon. Now I have an 04 swb reg cab 4x4 with the 4.7..It seems that Im only getting 12 miles to gallon now..It came with no service records..It has 114,000 miles. I just read online that these 4.7s should have plug change at 30,000. I thought all cars and trucks these days had 100,000 mile plugs from factory. Is it possible my spark plugs are the originals..My driving is mostly hwy. My old 5.9 would sometimes see 18 mpg on long trips..The air filter on the 4.7 is new. If plugs look good where else do I look?

 

You have to realize that you now have a 4x4. The extra stuff in the front turning robs you about 3-4 mpg. I changed the plugs on my hemi around 100k and gained about a mpg both city and highway. Those were the stock plugs.

 

Also, when you buy something used and dont know what has or has not been done to it, it is a good idea to do everything as if it had never been done

 

Or time to come to terms with the fact that... 12mpg .... Things are going well for you! I average 10.7 ... (95% city driving... well not technically a city, but my area of south jersey theres no such thing as giving one road no red lights with every other intersecting road having a stop sign) theres a stop light at every intersection... It blows. And mine is 2wd, Stick shift (should be better right?) Its also a quad cab, has 150lbs of subs/amps in it, 300lbs of sand in the bed, two bald tires on top of that (in the bed), along with 180ft of tow straps, and other miscellaneous must haves for my "Accidental Driving Habbits"

 

Yep, do not expect stellar mileage w/the 4.7L in the city. I get 10-12 in the city, depending upon how much I use the a/c in the summer. And my truck weighs in at a "light" 5420 pounds, with the topper.
I am at 30k miles now...guess it is time for a plug check. I am using the original plugs; I might file the ground electrodes smooth so that they have a clean edge again. Iridium plugs will not get you any mileage, but they do last a lot longer.
Weedahoe gives you good advice; flush the fluids and get your truck on a good starting point...

 

davb673... For the 20$ it will cost you to replace the plugs.... You're better of replacing them than you are to ground the electrodes smooth.... If you do that ... you may create a week spot that can cause the electrodes to break off... Trust me... i was cheap before with my dirtbikes cause at 32:1 oil/gas mixture iwas fouling plugs hourly.... Lets just say i lost more electrodes/(and the curved part the spark arcs too).......due to them breaking or not working at all (and yes i do know what im doing)... If you have access to a sand blaster however, it is a good way to make your plugs look/work like brand new.

 

The change interval on the 4.7 is longer than 30K. Even so, you're way due. A Sea Foam treatment is probably in order as well as air filter change. Like Weed said, assume nothing has been done in terms of maintenance.

 

Did a full tune up on mine, (iridium plugs, air filter, cleaned Throttle body and PCV valve along with IAC valve, replaced throttle posistion sensor, and cleaned recirc lines from the heads to the intake. Truck is an '03 Quad cab with the 4.7L and 3.90 gears and I get 15 MPG city and 18 Hwy.

 

well, I guess I should have been a little more specific..Most my driving is highway..So 12-13 was not cutting it..Anyways got around to replacing the plugs tonight. I actually think the original rc12mcc4's were still on the motor. Even at 114,000 miles. It appeared that the plugs never been changed. The 10mm nuts were stuck on the studs causing the stud to back out of the intake. The coils were stuck pretty good. Dont think I ever seen a Champion worn to a nub with a gap of .090 plus. So new ones at 1.99 each went back in nicely with some anti-seize. I did notice the engine firing right away now...hope to see improved mileage in the days ahead... Next on my list is gonna be tackling that creamy slime that gets in my oil fill neck..any ideas??

 

Make sure the lines coming from the valve covers going to the PCV valve/filler neck and PCV and clean clear and valve is clean (you can still hear the ball moving around inside). Monitor your coolant level to make sure you don't have a leak into the engine. These engines (4.7L) are susceptible to emulsion in the topend. Just check your dipstick periodically to make sure there is no discoloration. If you clean it out and it doesn't come back after a few hundred miles you are good. That is normal.