I have a 2003 Ford ranger XLT 4.0 two-wheel drive and I have noticed my check engine light has came on for System Too Lean Bank 1 and 2. A few months ago while driving from Taylorsville to American fork for a job interview my truck was fine. I start driving back to Taylorsville and I can't even accelerate. And it idled very poorly. I got it towed back home to Taylorsville (expensive) I try starting it right up and it starts right up and it ran just fine. I now got a job! Working in Provo my truck is running fine this whole time I don't notice any drivability issues. Except that System too Lean Bank 1 and 2 are coming on. I checked for vacuum leaks none whatsoever. All gaskets are good. I suspect fuel pump issue. Any ideas? Here's part of my freeze frame data.

 

Welcome to the forum

Simple quick test for a Vacuum leak is to warm up engine and let it idle
Unplug the 2 wire connector on IAC Valve, it will close
RPMs should drop to 500 or engine may stall, either is GOOD, no vacuum leaks
If RPMs do not drop you do have a leak

But 25% LTFT is a very BIG leak, and you are actually at 33+% because you need to add STFT and LTFT together on each bank to get actual level

So yes, it does "look like" a fuel pressure issue
2003 Ranger will run 55psi fuel pressure at the engine, there should be a test port on the fuel rail, looks like a tires air valve because thats what it is, a schrader valve
It would be worthwhile testing pressure

Low fuel pressure can be cause by the fuel filter or the pump........or fuel pressure regulator but thats part of the pump assemble in a 2003

Rangers just have fuel pump on or off there is no cycling of pump power(driver module) like in other Ford truck models

Rangers also don't have a fuel pressure sensor, computer just expects 55psi fuel flow at each injector, if pressure was 25psi then less fuel flows so computer has to add more fuel, thats what the +25% means, computer is opening injectors 25% longer than it had calculated for engine load

 

I unplugged the IAC valve wire engine stalled right away. We also sprayed around intake and vacuum hoses and gaskets. So all is good and sealed no vacuum leak. I am pointing to fuel pump or filter.

 

Yes, low fuel pressure would be most likely explanation at this point if there are only Lean codes to go on

As said, there is no fuel pressure sensor, so computer has no way to see low pressure, it can monitor other sensors like MAF sensor, so best guess at this point is low fuel pressure because it effects BOTH banks of a V6 engine

 

^^^+1

Recently had similar issues with my 3.0, although it never ran rough, it only seemed to stumble a little at higher rpms and started taking longer to fire over. New fuel pump did the trick.