99 xlt with 5.4 lt p0171 only. it started with what felt like a missfire or hesetation and ruogh idle. extreamly rough at 40-45 mph. but with no misfire codes just p0171 so all 8 coils and plugs and sparks replaced twice in one month. and still same code tested fuel pump pressure 28 psi.... removed cloged cats, still same code... new pcv valve and elbow.... checked for air leaks around intake and intake manifold and nothing.... clened mass air flow sensor...
i can unplug any coil on bank 1 and it wont make a difrence. but if i unplug anny bank 2 coils and engine makes a diffrance

 

The 171 code is for bank 1.
To confirm why, use a Scanner to look at both Long Term Fuel Tables.
You should see bank 1 at a shift of more than 25% confirming the code set.
With the table shifted, the fuel is too rich from those 4 injectors.
This causes upset in balance between the banks.
There could be a leaking gasket or even a faulty injector for a 1 bank issue.
To arrive at this situation, bank 1 Ox sensor would have to detect too much OX in the exhaust.
The system reaction is to shift the fuel table for that bank 'rich' in an attempt to correct for excess air it detects.
This shift is the 'end' result of the detection of excess Ox.
You have to find the cause.
Good luck.

 

Why are you wasting time with polls? Just troubleshoot it.