I have 2002 ford ranger edge v6 3.0 auto trans and I get p0171 code (bank 1 only) I already replaced MAF sensor awhile back, and fuel filter. I did have a vacuum leak with both banks a months ago, it was the brake booster. Lastly i found some screwed up something on my engine. I dont think is has anything to do with bank code.

 

If one of the wires is Grey with red stripe then that's the ECT(engine coolant temp) sensor, used by the computer to set Choke, this is a 5volt sensor

Red with white stripe wire is CTS(coolant temp sender) used for the dash board temp gauge, this is a 12volt sender

They look similar but are way different in how that work and what they are for

Wouldn't cause lean code but would cause rough running

 

I think its the engine coolant temp. Can we figure out the lean code?

 

Sometimes... fixing one problem solves many problems. Fix the coolant temp sensor. It's an obvious problem.

 

RonD said it would have nothing to do with lean condition. Also theres no code for the sensor so seems to work fine on the gage in my truck.

 

For the lean code, you said you had a vacuum leak previously (brake booster) and fixed it. Are you certain there are no other vacuum leaks? Did you try the "brake clean" check for other vacuum leaks? Lots of videos on this procedure.

 

Your temp gauge works off the sender unit. The computer gets the temperature info from the sensor that is almost gone. Was just recommending to fix it because it can only help.

 

I think i found the problem. I hear hissing from the general area. Then i pinch that red/black line then hissing goes away. The top wire on that ball thing.

 

The ball thing is your vacuum reservoir.

 

Those are plastic vacuum hoses that crack real easy when they get old. Easy to replace with standard vacuum hose at parts store.

 

The hiss stops when i pinch it. I'm confused because when i look at the long term fuel trim numbers they go up by 4-5% when i rev the engine. With vacuum leaks its usually the opposite right?

 

Short term Fuel trims(STFT) are the OPEN times for the injectors as calculated by the computer, STFT 0 is what computer calculated
Lets say calculated open time was 100ms(milliseconds), this is based on amount of air reported by MAF sensor(not really but close enough)

STFT 0 is burned in the engine, and O2 sensor shows high oxygen in exhaust, a lean burn, little oxygen is a rich burn
So if O2 reports high oxygen computer opens injectors for 102ms, a +2% increase, if still lean then 104(+4%),.......................
It does this until oxygen is just right a good burn

If O2 showed rich then open time would go down. 98ms, -2%, or 96ms, -4%....................

If there was unreported air coming in, a vacuum leak, then computers calculation is based on false data, there is MORE air than reported, so open time is not long enough, and that why STFT goes up, in the + range if there is a vacuum leak

 

where would i look for leak? Its only bank 1

 

I think its that line that comes out the vacuum reservoir i showed you. When i pinch it no more hiss.

 

Good place to start. You have a known vacuum leak there so replace the leaky line. Of course that may reveal another leak someplace else but you won’t know until you do.

Good luck!