I've been having this problem for a little while now and I have exhausted all ideas and what could cause it. I first thought it was the PCV system but after a massive overhauling of it I can find no leaks I never get system Bank 1 and 2 I only get system Bank 1 my mass airflow sensor is brand new and doesn't appear to be behaving strangely. I did notice when overhauling the PCV system that I do have a little bit of blow by on the passenger side that has caused a little bit more than normal oil to enter my engine that I have corrected with an oil catch can. the truck runs fine behaves like there's nothing wrong but every once in a while I get this code and it only has effect on my fuel trims that equals out for it to have pretty bad gas mileage it seems to do it randomly. I was wondering if anybody might be able to tell me what this could be. it happens once or twice every week and like I said the truck runs fine idles fine fuel Trims on idle look fine just every once in awhile it throws this code.

The truck is a 1997 Ford F-150 with a 4.6 that has been rebuilt but not by me we believe it has Mustang heads but it's still sporting the Ford F-150 intake my truck sits with just over 260K miles

 

What brand 02 sensors are on it?

 

Bosch they're both brand new left and right side I'm starting to suspect that it might be the header on the passenger side but the thing is I don't hear that trademark sound I mean occasionally my exhaust is loud but then goes away and that's usually during startup

 

https://www.obd-codes.com/p0171

 

Before assuming the fault is specific to bank 1 only, go look at the bank 2 long term fuel trim to see if it's normal or if it's also skewed towards the limit. It's not uncommon for one bank to trip a code first while the second is not quite over the limit but is heavily biased towards that limit.

While you're at it, pull the freeze frame data for the last MIL, assuming you haven't reset the PCM since then. If you have, you'll just have to wait until the DTC posts again.

 

This is some data I got today before I went to work this is the truck just sitting idling


Mil status off
ABSLT TPS% 19.2
ENG SPEED RPM 838
CALC LODE 27.5
MAF (LB/M) 0.73
COOLANT (F) 124
IAT (F) 37
ING ADV 14.0
ST FTRM1 5.5
ST FTRM2 7.8
LT FTRM1 23.4
LT FTRM2 19.5
VEH SPEED 0
FUELSYS 1 CLSD
FUEL SYS 2 N/A
O2S11 0.85
ST FTRM11 8.6
02S21 0.395
ST FTRM21 7,8
02S22 0.525
OBD2 STAT CA