My problem was a leak in the intake manifold. I finally could get a fluctuation in the STFT by spraying quite a bit of propane (with a weed burner, don't smoke while doing this ) in the V of the engine where the intake manifold gaskets are. I could recreate fluctuation in the STFT over and over again by doing this so finally decided to change the intake manifold. After doing that, I was good to go, so it was not the CATS for me. Have you had a look at the fuel trims?

 

Ok thanks Flyboy. That’s helpful info. I’m gonna get a proper scan tool where I can bee the fuel trims and o2 sensor voltage.

Then I’m gonna try what you did. Not sure about the use of Propane tho. Did you use a small blow torch can normally used by a plumber when he solders? or some other method?

I was hoping if i stick some brake cleaner in the V while watching the fuel trims maybe i could find something.

Im also gonna get a infrared thermometer and test the heat coming out the CATS to thoroughly rule that out.

Looks like i still have some work to do, but i’d rather flesh it out and come to my own conclusions than trust a guy who’s not gonna work as hard as me to figure it out.

 

You can try a small blow torch. Guess it depends on where and how big your vacuum leak is. I had to use a weeder burner, hooked up to a 5 gallon propane tank. My leak was probably farther back and needed more propane to reach it. The burner puts out quite a bit of propane. Little risky I know, some guys wouldn't do it, but worked for me. I just hit it with a bunch of propane in the V of the engine for a few seconds, while watching the fuel trims. The computer is going to try to compensate so don't expect a huge pronounced jump.
For example, if your STFT are showing +25% and you hit it with propane and it fluctuates down to +23%, then you have found a leak. Don't expect it to stay at +23% as the computer will compensate and the gas will dissipate so you have to be keeping an eye on your fuel trims. If you can recreate that scenario over and over on your scanner, then you probably found the problem and is probably the same as mine.
If it was me, I would totally rule out the intake manifold before moving onto the CATS, cheaper and intake is more likely to be the problem in my mind. I assume your truck has never had the intake replaced and has a few miles on it.

 

Don't use a liquid spray, use propane.

 

Stripped spark plugs holes

I have a 99 expedition Eddie Bauer 5.7 l here is the good news that motor can reach 500,000 miles here is the bad news they designed the engine where the spark plug has 12 threads in the spark plug threads on the motor only have 4 threads so you will shoot spark plugs left and right according to my friend who put 500,000 on one himself it usually shoots on the two spark plugs I have already shot to myself you need to buy a kit to retap those threads and put the adapter in you can get them out of O'Reilly's hope this helps and forgive the speech-to-text spelling but once you fix those threads and put the adapter in there which you can do by yourself you're a gun to notice much better compression by the way I was reading him reading the same codes fuel too lean and went through everything myself to try to fix it not only thing that improved is when I fix those spark plug holes

 

Ford never had a 5.7.

The topic of blown spark plugs has been covered here a lot. You can't just retap the threads, you need to use a TimeSert or Lock N Stitch insert kit. Other inserts don't last. If you torque the plugs to 28 ft/lb, blowouts will almost be completely eliminated.

 

so you bumped thread thread from 2015, to spew false information?


#FAIL