I have a 1996 Dodge Dakota sport, 3.9 V6 4WD manual, and it has over 200,000 miles on it. Recently, the check engine light has been coming on, I use my own OBDII scanner to view and clear the codes. It is P0171 System Too Lean Bank 1. I have already replaced both oxygen sensors, but it still throws the code. On the live data, it shows the LTFT at 16.4% and STFT anywhere from 0 to 20%.

It starts, idles, and revs completely fine, but does have noticeable power loss when I'm accelerating and hit around 3000 RPM.

Here are a few screenshots of my live readings.


At Idle


At ~2500 RPM

Despite what those logging times say, these screenshots were taken after the engine was run for a while and fully warmed up.
Also, the green is downstream and orange is the upstream O2 sensor.

Could this be a fuel problem? Like low fuel pressure or dirty injectors? I am completely lost. If anyone has any ideas about this, please let me know.

 

Yeah, I think the first thing I would check is fuel pressure while driving it. Get a gauge with a long hose you can tape to the windshield, so you can see what it's doing while you are driving.

 

Also, check for a plenum leak on that side. Plus check for an EXHAUST leak on that side upstream of the O2 sensor. Or just downstream of it.

RwP