System Too Lean Bank 1 and 2

[Bee&Optimus2003]

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. I have more freeze frame data if needed.

 

[Sharky]

when my 2004 had this same issue it turned out to be the fuel filter. located on the frame a little behind behind the cab.

 

[rubydist]

And it also could be the oxy sensors are bad, although it is rare that they both go bad at the same time.

 

[Bee&Optimus2003]

And it also could be the oxy sensors are bad, although it is rare that they both go bad at the same time.

I replaced the upstream O2 sensor a few months ago.

 

[Ripdog]

They say if you don’t change them in pairs either upstream or downstream you may get codes as the new one reacts faster than the old one.

 

[Dirtman]

There's not enough information to go on. Both banks lean means an issue common to both so not fuel injectors, o2 sensors, exhaust leak, etc.

Most common reason would be a vacuum leak. A simple way to test that theory is to run live data with the fuel trims brought up and rev the engine. If the fuel trims drop when the engine revs then its almost certainly a vacuum leak.

Could also be a fuel restriction from a weak pump or clogged filter. No point guessing on the filter, they are less than 10 bucks and take 2 minutes to change so just do it. Check fuel pressure with a gauge (should be 65 psi) and barely drop if at all when you hit the throttle.

Could also be a MAF sensor under reporting air flow. Clean it with MAF cleaner and see if anything changes. MAF should be cleaned once a year anyway.

 

[Bee&Optimus2003]

Shouldn't fuel trim be near 0% normally? If so my Fuel Trim is near zero (less then 10%) even with throttle.

 

[Dirtman]

STFT and LTFT are your fuel trims. Yes near zero is ideal but you're showing +25% long term and +9/7% short term so your combined fuel trims are over +30%. You need to look at BOTH numbers and add them together.

The code for lean is set because the fuel trims are beyond what the computer is capable of adjusting for. The long term trim maxes at 25%.

Short term fuel trims should usually always be bouncing slightly positive to negative but averaging zero. The long term is the computers memory as it adjusts for the age of the engine so these numbers can creep higher or lower but generally if they are around 10% + or - and the short terms still stay near zero there is nothing to worry about.

You have something to worry about lol.

@RonD could explain this better.

 

[Bee&Optimus2003]

Sorry I should have explained better. When I had someone else Drive yesterday I'm monitored the live fuel trim numbers. We did freeway driving short-term and long-term stayed near zero they never creeped up. so something is causing it to be all the sudden lean for like a split second. And I think it's happening one day in a week.

 

[Dirtman]

Check the evap purge solenoid, purge line and vent solenoid. I would expect to see an evap leak code BUT if the purge valve or line is broken, or vent valve is stuck open, when the computer commands the evap system to purge you would experience a temporary vacuum leak causing a lean condition that would then go away when the purge is complete.

I can't really think of anything else that would cause a lean condition to come and go at random. The evap system is the only thing that comes on and off at different times and would expose the engine to a leak.

Possibly an intermittent fuel pump failure as well, but hard to diagnose that. And fuel pumps usually just up and die completely.

 

[Bee&Optimus2003]

Considering the evap monitor hasn't completed yet. (Been about two weeks) I will check evap system. I will post back.