I have a 2002 F150 4x4. 4.6 auto. Bought the truck used with 35000 miles on it just based on my '97 experience. Same truck, setup only white instead of black and 3.31 rear instead of 3.73, both are work trucks...tool box, ladder racks etc..... I was getting around 16 MPG in this untill one day passing someone it felt like I lost half my power. MPG dropped to 10.5-11..since then EVERY SENSOR has been replaced, new fuel pump, pressure reg., fuel lines, every plug, every COP, EGR valve, throttle body, and PCM, cut off the cats and replaced wit 2 high flows and cut off the muffler. Ended up blowing the engine(probably from WOT to just almost keep pace with traffic) Replaced that with another with 50000 miles on it. Still didin't help. Replaced all 4 calipers and brake hoses????? replced tranny in case that was hangin up..Same problem, still weak, still 11 MPG driving city or highway, easy or hard. DTC started with misfire, everytime something was done to fix a problem a new DTC would pop up untill the PCM swap. Since then only the 1401 for about six months, (I gave up for a bit)decided to try the Motorcraft DPFE Friday and boom no CEL for 300 miles till today, now I have 1401 AND 420, I feel like I'm back to the "fix this DTC so we can get a differtent DTC" game again.??? any ideas short of cash for clunkers??????????? I want this body style not the newer, I'm into this for about $8000 but the truck is almost brand new again and on top of that I hate to be defeated. Call me stupid if ya want but any ideas would help I don't know whats left.

 

Welcome to the site!

I think you dropped a valve when you heard the pop. After replacing the motor and all the stuff you have replaced I'm at a loss. Experts chime in.

 

Is It possible for the exhaust to be too free flowing? On one board someone said the 420 code comes up when the 1st O2 reading and the 2nd O2 reading are too close to being the same, is it possible the Cat is not able to do its job if the exhaust is passing through too fast?????? just grasping at straws here.

 

You might have just have horrible luck and ended up with a second motor that was shot? I hate to hear stories like this.

 

I would suggest new exhaust...I was having similar issues with my 03 Fx4 and it turned out that all the baffles were clogged...just mu luck though...but they will check it for free

 

Do a compression check....

 

Changed the dpfe to a motorcraft, mileage went up to 12.5 over 4 tanks. Took off the throttle body, cleaned it along with my ports...not clogged but dirty, used a coat hanger to clean the tubes that run to the dpfe and have been getting 14-14.2 through 9 tanks. I haven't seen the trip odo pass 300 on a single tank in a long time. P1401 has been gone for weeks but now I'm getting P0420............still happy though, a 3 mpg increase is a lot considering I use almost a full tank every day to day and a half. I'm putting a muffler back on, for says not enough back pressure or too free flowing will not let the cats heat up enough so by slowing things down that might fix it. I have 2 high flow cats and thats it right now............