I dropped a 99 5.4 into my 98 f-150. I added long tubes, Denso plugs per Mike Troyer's recommendations with Accel wires from Mike with the stock 4.6 coils. I had a local guy tune the engine for 93 and 87. It ran like a scalded dog from 2000 rpm up, but was poor under 2k. I thought the original tuner might have missed something so I had Mike also make a 93 and 87 tune. The 87 tune pings like hell and is being reevaluated. The 93 tune runs a little better than the other 93 tune I had, but the bottom end is still about the same.
My low end power issues are very similar to what this thread was about:
https://www.f150online.com/forums/v8...ower-gone.html
Unfortunately the owner never posted any improvements.
My 4.6 was 100% perfect mechanically when I pulled it, but it too was down on low-end power. The idle was/is at times a little rough on the 4.6 and now on the 5.4, but is not noticeable to the average joe. I have no codes. My coils have 89k miles. When coils go bad, is it across the entire RPM range or one specific area?
Will dirty injectors cause low-end issues?
I pulled the IAC and cleaned it. It wasn't very dirty, but I don't know if it was functioning correctly.
I cleaned the MAF.
I have not checked/cleaned the EGR, dpfe or EVR.
I did have a broken vac line that I fixed. I will tape the joints to ensure no small leaks are present.
The 5.4 engine has 100k. It's no spring chicken, but I would think if 2k rpm up is good, 2k down would be good too.

HEEELLLLPPP! Thanks!

 

The headers usually decrease low end torque and help it in the higher rpm.

 

whats your gear? That might be the answer..

 

How many miles on your 02s?
some live date would certainly help

 

O2's are original so 89k.
I'm strongly thinking spark or fuel issue, but I don't have experience with coils crapping out or injectors with excessive funk.
I have seen a few other posts of this issue at about the same mileage, but no one has posted results other than one guy who cleaned his IAC.

 

weak cops


lack of maintenance


Poor fuel


torque converter

 

-Does not have cops.
-I almost always run BP from high traffic stations.
-I consulted Hughes on the converter before i made the swap.
-What maintenance issue would cause loss of low end only?

 

...missed the point you swapped it

 

might be tune related...