Havent posted in a really long time here. I searched the posts and have a few ideas what the issue could be but nothing definitive. I have a 2005 FX4 screw 5.4 with 163K. I am the original owner and the drive train is completely stock / no mods except for an edge tuner which has been in the towing mode since i bought it on a group buy here when the truck was new.Plugs were changed at appx 90k and the cops were changed one by one between 90 and 100k. Fuel filter changed again about 5k miles ago. I never had any real problems and now having some ( hopefully) minor issues.
Around April the truck started to feel like the cops were crapping out again (like they did around 90k) and at 1st there were no codes thrown. The truck started to have no top end and would sputter and even back fire if i stayed in the gas pedal but if i backed out it would smooth out so i knew an issue was brewing ( this didnt happen all the time). I was waiting to see if a cop or something else failed but it took until June to throw the p0171 system too lean bank 1 code. End of June is when i 1st saw the p0420 catalyst system efficiency below threshold ( bank 1).
Now it is slowly getting worse. The p0171 no longer is there but the p0420 comes every few days. I clear it out and keep note of when the code is thrown. The truck feels like it is losing the bottom end power.Sounds like a 4 barrell carb from a stop and is just flat. If i feed it , it will go and can even feel fine at times but i need to figure this out as the truck is my daily driver.
Im thinking i should do the plugs and cops again as maybe one or both of these are an issue? Do any of you think this could have caused the O2 sensors on bank 1 to have a problem or possibly the cats to fail on bank 1? I hate to throw parts at it but figuring i have 70k on these plugs it wouldnt hurt and while i have them out do the cops also. Any help, suggestions or what else i can check would be appreciated.

 

Sounds more like plugged cats to me. Have you ever had to change any injectors? The 05 5.4 had a bad batch from the factory, they would stick open and run rich, which can plug the cats.

 

Read these for clues.

https://www.obd-codes.com/p0420

https://www.obd-codes.com/p0171

I would be suspicious of the injectors since the 2005s got some bad injectors. That could have caused the p0420 issue.

 

The apparent cat failure is likely due to the engine running for an extended period of time with either a vacuum leak or misfire on bank 1. This causes excessive fuel to be dumped into the cat and leads to its eventual failure. Usually, that failure only makes the cat chemically ineffective but, in some cases, there's enough extra heat generated by the fuel burning in the cat that the substrate is damaged, either by melting it or by causing it to physically degrade and crumble. Either of those two events will end up causing a restricted exhaust flow and that, in turn, will manifest as a poor drive-ability condition since the engine cannot properly "exhale".

Take the truck to an exhaust shop and have the converters and the rest of the exhaust flow tested. That will tell you what you need to know about what's gone wrong and what will be needed to repair it.

 

Thanks for the help...Never had to change any injectors. Is there a way i can tell if one is stuck open or just failed? Maybe i need to start with an exhaust shop to see if the cat (s) are clogged..

 

Thanks for your help. I believe you are correct with the misfire on bank 1 causing an issue. I will find an exhaust shop and hopefully they can do a flow test and i will go from there.