My truck is running good but decided to check LTFT and STFT. Bank 1 looked good but bank looked to me it was running rich also the O2 sensor was way out too? Im not sure what can make a bank run like that. Any ideas, here's some pics

 

What year and what engine?

just FYI,
O2 sensor 1(S1) = upstream, near engine sensor
O2 sensor 2(S2) = downstream, after Cat sensor

So B1S1 is passenger side upstream sensor
B2S1 is drivers side upstream sensor

B1S2 is downstream sensor
B2S2 is downstream sensor<<< was only on dual exhaust systems but in later years there were 2 on single exhaust as well

O2 sensors generate their own voltage once they are HOT, 650+ degF, they can only see oxygen(O2) not fuel
0.1volt is high oxygen, often called Lean, but doesn't mean actually Lean
0.9volt is low oxygen, often called Rich, but doesn't mean actually Rich

Lean and Rich are terms people usually associate with fuel, fuel mixes, and that's not what this is, if a cylinder misfires then no oxygen was burned up, and that oxygen is dumped into exhaust, O2 sees higher oxygen so lower voltage and "lean", but its not really lean its actually RICH because of all the unburned fuel from the misfire now in the exhaust, lol

Upstream sensor voltage should go .2v to .7v very very fast, that's normal

Downstream O2 should be steadier and 0.7v to 0.8v as the Cats burn up most of the oxygen as they burn up pollutants, so not "rich" just low oxygen level

O2 sensor last 100k miles or 12 years, which ever comes first, they simply run out of the chemical to detect Oxygen


STFT(short term fuel trims)
Fuel trims are the OPEN time fuel injectors
Computer calculates the open times for fuel injectors ON THE FLY, based on air weight(MAF sensor), air temp, RPMs and engine load, also fuel pressure and injector size
That calculation is 0 STFT
After injectors are opened the computer watches O2 sensor voltage, if the average is low then computer increases, STFT to +2, if still low then STFT +4, and this IS a percentage, injector was open 4% longer than calculated, so 4% more fuel was added
If O2 voltage was high then STFT -2%, then -4% then -6% so injectors are closing 6% sooner, adding less fuel that computer calculated

LTFT(long term fuel trims)
These are the average of STFT over time, AND is added to or subtracted from STFT during STFT calculation
So if LTFT was -15% and STFT was -5% that's a TOTAL of -20%

LTFT is so engine runs better cold before O2s can be used, and so the computer doesn't have to start from scratch as engine gets older, lower compression, small vacuum leaks, higher or lower fuel pressure, ect............

And all the above is only accurate after engine is warmed up, ECT sensor above say 160degF, 185degF is best

O2 sensor B1S2 looks to be dead, downstream O2, could be unplugged but should get .00, and should also set a "no switching code" lean

You could have higher than expected fuel pressure, that would cause -XX STFT and LTFT
1995-1997 was 30-40psi
1998-2011 was 50-60psi

All have fuel pressure regulators that can cause higher pressure, the fuel pumps themselves can do 80+ psi in any year


If an engine is actually running Rich you will get Smoke out the tail pipe, greyish smoke
If an engine is actually running Lean it will ping/knock, especially when accelerating

 

Hi Ron, 2001, 180,000mi 3.0 motor its a B 3000 to me the right and left side are so different if it was fuel pump or filter etc, I would be both sides? looking a the scale LTFT bank 2 is -19%. isn't around 20% when they will throw a code?

 

the pics are all upstream sensors. B1 and B2. B2 just seems to be all over the place?

 

I just read your reply closer, I'll check closer I didn't intend to to O2 B1 S2 downstream. I see that thanks. will test again soon.

 

Bank 1 and 2 upstream. This look ok to me?

 

Yes, looks OK, does look like either is biased low or high, they look the same for both banks

 

At 180K miles if the O2 sensors have not been replaced you should replace them as they are a wear item.

 

I think for now I'll just keep my eye on them, Im thinking they have been replaced, they look too good for being 20yrs old. the motor runs real good, the best it ever has, it needs radiator flush for rust that I saw when the heads were off. oil change and filter and just put some miles on it, Thank you for helping me diagnosis all my issues and in a few days there really wasn't any big issues, start with the basics and go from there.