What’s up new to the forum and I’ll try to make this a clear as possible. I just purchased a 01 f150 5.4 4x4. This truck starts right up, idles great, engine sounds great and idles very smooth. When I got the truck it did not have ac and I replaced the compressor. Issue was present before and after compressor but is worse now that the ac is working. Vehicle had a p0171 and P0174 codes when I bought it. I cleared them and have gone about 1k miles and they have not returned. I live in PHX and it’s regularly above 110-115. The issue I have is after about 10-15 minutes of driving the truck feels like it has 150 hp and shifts smooth but higher at 3k rpm and the fan just roars. I replaced the PCV valve because it was leaking and no change. The pcv hose to tb does not look cracked but I have another one on the way. I’m going to smoke the truck and tonight and pull 02 sensors to see if it’s a cat converter issue or vacuum leak. I have no misfires and I’m getting about 10 mpg. I’ve had multiple 10th gens and my old 10th gen on 35s would smoke this stock on and get better mpg. Per scanner idle is 675, fuel fuel trims look good as well as 02. -11 vacuum at idle and 0 to +3 wot. What are some other issues to look for? In regards to TSB 2-12-03 to what negative degree would the ecu retard timing to? Would the issue described in this tsb kill 100 horsepower or is it another issue?

 

Check the rubber elbow in the PCV hose where it connects to the intake. You can get the entire hose for about 25 bucks.

 

I have one in the mail but the current one does not appear to be damaged.

 

Could the cats be plugged? When I bought my 02, it was down on power because the air filter was extremely dirty. The PO lived on a dirt road.

 

air filter is not the cleanest I blew it out yesterday. I’m going to pull O2 sensors tonight and drive it around to see if it still has the issue.

 

Best way to check the cats is take it to a muffler shop for a backpressure test, you can also use an infrared thermometer after driving it hard to see if they are excessively hot.. If you pull the O2 sensors it's going to run like crap anyway.

 

So I smoked the truck and did find a vacuum leak coming from the throttle body. Replaced the hose and also replaced the pcv valve and the hose and I can’t see any more leaks. Replaced maf / air filter today and no difference. My lean codes have not returned after about 1k miles but I still have no power. On acceleration timing goes negative or to 0 and load goes up to about 93%. Could this spark / coil issue even though I don’t have misfires?