I have been experiencing really bad gas milage on my truck. It is a 2005 f150 5.4L 3v triton with 156000 miles. I have done just about everything to try to make it run better(I'm getting 13.5 and I have been getting 16). I've changed all the spark plugs.I put all Motorcraft in. I changed all the COP's to MSD. I changed all the fuel injectors to BWD. I changed the O2 sensors (4). I changed the air filter to a K&N. I even took off the MAF sensor and cleaned it really well. I also replaced the fuel filter. It also has a small rough idle going on. The dealer told me it was normal but I don't believe him because my dad's 5.4 idles smooth and has great milage for an F250.

What is there left to change to make the truck get the milage back? If any?

 

Put a bottle of Gumout for high mileage engines in a half tank of gas and run it through. It cleans the intake valves, ports, and combustion chambers. MSD cops may not be the best.

 

And get rid of that K&N filter if it is a drop in type. I had one in my 05 and it didn't seal letting dust get past. If it is the CAI type, you need a tuner for it otherwise it will run lean, did the same thing to mine but besides running rough at high RPM, loss of fuel mileage, it also fried two sets of plugs.

 

I was told that MSD are the best because they are high performance coils and have a secondary coil but I'm not a gas mechanic only a diesel mechanic. My question is how will it help the intake valves when the gum out goes in the gas tank and only gets injected by the injectors? Jw cuz I don't know.

 

Has the throttle body been cleaned? Have you possibly installed taller tires?

 

Thanks for the heads up. I will replace the K&N filter with a fram one tomorrow and let you know if it gets better.
Should I reset the computer since I changed my oxygen sensors too?

 

Nope. Everything on the truck is completely stock. It's only a commute to work truck. What is the throttle body and where is it located and how do I clean it?

 

Don't let a Fram anything touch that engine. Get a Motorcraft or Purolator.

If you didn't use either Motorcraft or Bosch O2 sensors, you made a mistake. I also question BWD injectors.

The throttle body is on top of the intake. It has to be removed to clean it - with throttle body cleaner - and do NOT move the throttle plate with it disconnected, you will kill the electric motor that operates it.

 

MSD stuff usually has a short lifespan & can fail at anytime! Mustang folks have little respect for them but they LOOK nice! I know all the hotrodders put the 6AL MSD's in high performance engines but they are always working on their cars anyway. Ford OEM is hard to beat unless you have a specific need.