I'm chasing code p0171 on a '02 ranger 2.3l. My spark plugs are burning black my tailpipe is black,as well as the rear 1/4 of my truck where the exhaust exits. Replaced maf, both O2 sensor, tps,map sensors. Oh yeah, coil pack and plug wires. The spark plugs go about a month before randomly fouling out

 

Welcome to the forum

P0171 System too Lean (Bank 1)...............only bank on a 4cyl engine
Code indicates higher oxygen(lean) in exhaust than lower oxygen(rich), this is from the upstream O2 sensor, so shouldn't be black spark plug tips or exhaust

Because of this code the computer will be adding 20-25% more fuel, causing the Rich running, if its a FALSE LEAN

And it is a false lean if spark plug tips are black and you see smoke at the tail pipe

Replacing all those sensors was not good, it can multiple issues as "new sensors" are unreliable unless they were Motorcraft(or OEM) brand, and even then its a roll of the diced

Best path is to get an OBD2 reader and check what all the sensors are telling the computer
Bluetooth OBD2 reader(ELM327) is $15, and APP is $5, $20 total, so cheaper than any new sensor

Upstream O2 sensor would be first stop for Lean or Rich codes
O2s generate their own voltage when heated above 600degF, so engine must be warmed up to check O2 sensor voltage
0.1volt is high oxygen or lean
0.9volt is low oxygen or rich

So if O2 is showing under 0.2v all the time then computer has to add more fuel, all the time
A new O2 sensor can be bad out of the box, any new sensor can be, so you need to look at data from each sensor to see if it makes sense

Other issue could be oil burning, this will cause black spark plug tips and black exhaust
So are you losing oil?
When was the last time PCV valve was changed, Ford says every year on this engine, but every 2 years on the 2.3l SOHC Duratec should be OK, but it MUST be changed
Its a pain to get to on Rangers but needs to be done