As the title says I am dealing with high fuel trims. At idle bank 1 sits at 25% and bank 2 sits at 21%
1500 rpm bank 1 sits at 21% and bank 2 sits at 20%
2500 rpm both banks sit at 18% and any higher they go back up.
does anyone have any clue as what could be causing this? Truck is 1998 F150 5.4 V8 Lariat.
//UPDATE// I have done a smoke test and couldnt find any bad lines. I did the carb cleaner method and had no surging. At this point I think it's a fuel issue.

 

So it's only Bank 1 that has the problem? Leaking fuel injector?

 

it could be a dirty injector. Idk though I'll go and replace my fuel filter to start and check prices in injectors.

 

No codes?

 

it throws the P0171. I replace both O2 sensors already to include MAF, and airfilter

 

P0171 is for bank 1. Are you receiving a similar code for bank 2? Read this if you haven't already.
https://www.obd-codes.com/p0171
What is the fuel pressure?

 

Haven't received a bank 2 yet

 

Replacing the O2 sensor for a P0171 is a waste of money. Check the PCV elbow behind the intake.

 

If you're only getting the one side code, the problem is not likely the MAF, fuel filter or an air filter. Those are items likely to affect both sides. And since you haven't found any air leaks, i agree with the idea to test/check the injectors on the bad side. Make sure they are all working. There are some tutorials on line for how to test them.

 

I do need to check the injectors. Now seeing as I don't have a P0174 for the bank 2 side, the bank 2 side however does have high long term fuel trim also. Stays at 21 goes to 16 at 2500 rpm

 

Exhaust leaks before the upstream O2 can cause lean codes. Looks like both banks are affected, it's just bank 2 hasn't reached the threshold to trip a P0174 yet, so don't rule out a vacuum leak or leaky intake gaskets. Throw a couple bottles of Techron in the gas to clean the injectors.