Got these codes. Replaced all four oxygen sensors. Codes came back. What else could it be?

Thanks,

WOW
Will Walker

 

Those codes do not indicate a faulty sensor. Unfortunately most auto places who pull codes will interpret it that way. Well, now you have new sensors.
Those codes point to a few things that need to be looked at. The first is a vacuum leak, check all the pcv routing around the throttle body for leaks. Especially the elbow in the back. It is a lean condition effecting both banks. Clean your MAF sensor (there are "how to's" if you need them) When was the last time the fuel filter was changed?

It is more than likely a vacuum leak

 

X2 on the vacuum leak.

 

Thanks for the replies. Where is the MAF on a 5.4? I know where the throttle body is. I found a cracked vacuum hose and replaced it. Codes came back after 10 miles of driving. Toyz, where are the "How Tos"? I can't find anything on cleaning the MAF.

Thanks,Will

 

Scroll down the forum index, you will find them.

 

https://www.f150online.com/forums/ar...03-f-150s.html

I would still suspect a vacuum leak at another source. It is best to fully remove and inspect the pcv lines that route to the rear of the throttle body as sometimes they are hard to find the leak. They tend to crack on the inside of the elbow, which is way in the back and hard to reach. It should pull straight off. Remove the whole system and inspect it. I have seen throttle body, egr or iac gasket leaks also cause those codes. Any un metered air forward of the maf will set off a lean condition. And they are most common. Still doesn't hurt to do the other things though.

 

I see that you already have several good replies to your question. I agree with them all. You might find yourself ahead of the game a bit if you can replace all of the vacuum hoses on top of the engine. Its a very good preventative maintenance measure for any 10 Year or older vehicle.
Peace

 

I would look at the PCV valve and associated plumbing especially the elbow behind the engine. Some other areas include EGR plumbing, AIC and associated plumbing. Finally possible intake gasket leak or cracked manifold. I replaced all of these on my Expd, and ended up finding a cracked intake manifold. Get some starting fluid or simialr and spray around intake and hoses to check for leaks. If you have a leak the engine will change pitch when the spray hits it.

 

Use throttle body cleaner instead of starting fluid.. less chance of damaging your engine

 

save yourself the time i have had the same problem for years..its the isolator bolts under the intake manifold..im looking to replace mine this summer when i have a little more free time to do the job..its a VERY common code for these years 4.2L..ford just cheaped out and never recalled the issue.

 

He has a 5.4 not a 4.2