Well the old girl is about to crack 98,000 miles. She's been a dandy so far, my 04 SCrew with a 4.6. Other than the original brakes sucked big time I haven't really had to put much into her to keep her running. So I made the decision to keep her a while longer and started to replacing some of the wearables before I have no choice about it. I call it maintenance. Today I replaced the O2 sensors. That's a pretty much straight forward repair except that Ford apparently forgot the anti seize on mine. I had to use a hot wrench to get them off. I replaced them with Motorcraft parts to keep the old girl happy. What I didn't expect was the slight miss that I had at idle went away. I have noticed the fuel mileage has been falling too as well as power and figured it needed plugs again. The power is back and then some. I really don't remember the engine running this good although it's never run bad. It looks like the fuel mileage is back or maybe even better. I put close to 100 miles on it today and the gauge hardly moved. I guess I'll find out in the next few days. So if you are at 100,000 miles or more and are lacking in power and fuel mileage and maybe a slight miss, you might consider changing the O2 sensors. Sure worked great in mine.

 

Awesome man! Hope you get many more miles outta her

 

you change all 4 or just 2?

 

yea, all 4 or 2??? I'm thinking of changing mine on my 03 5.4L to improve fuel mileage. Keep us updated--DirtySCREW

 

Just changed the front 2. The back 2 just ride and check the function of the cats. I had no CEL and never have had one on this truck. I did not expect any changes in the running of the engine at all. I just didn't want to look at a CEL down the road as I'm on the hiway a lot and not necessarily anywhere near a major town with a dealership. FWIW, the fuel mileage started to drop about 20,000 miles back and the power has been also going down at about the same time. The power loss was nothing drastic just the truck wouldn't pull hills in OD that it did before at the same speeds without down shifting. I had thought about changing them back then but never got around to it. I guess it's cost me in the long run in fuel.

 

thanks

 

change your front o2's every time you change your plugs...

 

Im going to change mine even sooner then. 184k on the originals

 

lol, 205k on my originals

 

When and/or if does anyone ever change the back (downstream) two?

 

I changed mine in the back. I have read before that they can effect mileage, something to do with switching rates, but I'm not positive. The reason for mentioning this at all is because this info was from trusted tech, that I do remember.
I'd have to suggest googling that, there was something that made me want to change my rears with the mileage I had on them when I changed out the forwards. The truck does stick right around 16 mpg , City and Highway.

 

I'd only change them if you throw a CEL with a code that shows a fault in them.

 

I picked up a couple new O2 sensors cheap off ebay (Bosch) for about $50 delivered and replaced my front 2 after approx 139K miles. Not sure if the mileage is better yet, Putting new rebuilt fuel injectors did help the mileage, about 1 mpg better.

 

Just an update. I've been driving my girls econobox Focus from the ranch to San Antonio and then driving the truck in town. Man, those folks in town are clueless drivers! Anyway, it's taken this long for the me to get enough miles on it to warrant putting gas in it. This is for town driving- combined sitting in traffic and expressway- 21.2 mpg. That's up from around the 16-17 mpg mark. It runs like a new one. Lots of gitty up go like it did in 2004. I may have to make a run to Michigan next week and if I do I'll be taking the truck. I have the girls grandmother to see before she cashes in. The doctors gave her 4 months. So I'll probably get to really see what kinda mileage she's capable of. So far, it's been THE thing to do to make this truck great. If yers feels a little lazy and fuel mileage seems off, I'd recommend not waiting for a CEL. Change the O2 sensors out and use Motorcraft parts.

 

PART NUMBERS anyone???? I called AA and all they have is Bosch for $89 EACH!!! I've looked online but am a little confused as different part number says the fit the same vehicle model years. Anyone have Motorcraft part numbers for a 2003 FX4 Lariat 5.4L???--DirtySCREW