Just bought 2004 F150 Lariet 5.4 pulled codes p0171 and P0174 Ford store says I need to replace all 4 cats Hard to believe all 4 went out at the same time. Any thoughts on this THX truck has 82000 miles on it

 

First thing to do is look for a vacuum leak that may affect both banks of the engine. Also low fuel pressure or a mis reading from the MAF can give those codes. If you do not have an emission inspection soon, erase the codes and see how long it takes to return.

 

Its not your cats...
It is most likely that the MAF sensor is dirty. If you have an oiled air filter (K&N) and over oiled it it would cause the MAF to get dirty. In most cases like this just cleaning the MAF will fix the problem. Clean it with brake cleaner, or electronics cleaner if you have any. Make sure that it is COMPLETLY dry before you reinstall it.
So... check the MAF, the air filter, and make sure that there isnt a vacuum leak before the MAF also. it might also help to check your fuel pump and filter, and possibly injectors too if that doesnt work. It is reading to much air, and not enough fuel so its either one or the other or both! I hope that helps. at least it will be cheaper than all four cats.

 

Put a new maf sensor on the light came back in about an hour. The dealer did not charge me for it so lucked out there. I have a ford mech of 20 years working on it after hours he hooked a computer up and we drove it while hooked up The fuel pump was good the filters clean. Seems like when you first start truck it idles good but the longer it runs the worse it gets and then will shut off. Will crank right back up Before it shuts off it starts to stumble or run rough and then wam off she shuts off He said the injectors were checking good also

 

Check if the EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow). could also cause the Ho2 sensors to tell the PCM that it is running to rich, or to lean. It is fairly common when this happens to trucks (over 60,000 miles), and it is usually the DPFE (Differential Pressure Feedback EGR) malfuctioning and sending to much, or not enough exaust back into the intake. Try this, and see if it fixes it. I will try to find out more if it does not. Goodluck!

 

Just talked to the local Ford store they say this truck has no EGR or DPFE valve

 

dont know how cold it is were your at ,but the upper intake gaskets have a tendency to shrink when real cold ,this is when they leak as engine warns they seal , this throws the fuel trims out of wack long enough for pcm to try and make correction, also hope your not running e85 this also causes lean concern, you said you replaced maf, just make sure there are no vaccum leaks for pcv ,air cleaner lid is succure,all clamps fitting the air snorkle tube are tight for unmetered air

 

That makes sence. Ide deffinatly check the gasket, and make sure that you dont have any vacuum leaks ANYWHERE before the MAF that might cause the PCM to over compensate.

 

Does your friend have a scanner that can read snapshot information? You need to know the conditions present when the codes are set. If it is when the engine is warming up, you may have a problem with the intake gaskets. I would look at the pcv hose where it attaches to the back of the intake manifold. There is a rubber elbow there that deteriorates with time and gets a small pinhole in it. I sell a number of these.
And no on the cats, they will not set a lean code. Can't even believe the dealer told you that. Doubt if I'd go back to them for anything.

 

This is why these forums are valuable. Had the 0171 - 0174 codes come up on my '04 v6. Mech #1 says replace intake manifold and all vac hoses - $650. I says go pound salt. Mech #2 says it's your mass airflow sensor - $110. I looked on an online forum and learned it's most likely a vacuum leak. You can do a smoke test for $75. Or...

So I took a good look and eureka - the boot connecting pcv valve to manifold has a rip. Repair cost - $2.50. Runs like a champ.