Wideband and fuel trims dont match?

[GTPDisaster]

I was looking at a scan I did yesterday and most of the wb readings show 14.8-15.0, which is lean, and the NB o2 is reading in the 500's which makes sense, but then in the same cell on my ltft table its showing negative values, so its pulling fuel right? Why would it be pulling fuel if both sensors show a lean condition?

So either im thinking of this the wrong way or something isnt right. Posted the log if anyone wants to look at it for me.

edit: err unless high 500s is sligthly rich I guess that would a lil more sense

[popeye55]

Not to insult you but is everything in check.

NB O2's are good
When you set up your wideband did you check for any offset"not sure what type WB you have. If not search WB error on the process and histo's.
What is the location in comparison to the NB
Are you resetting your fuel trims before each log?
Why are there no STFT's? Are they off for some tuning reason? If you are logging I would think you would get my accurate and quicker fuel trims if you shut off LT's and turned back on STFT's....only my 2 cents.

[GTPDisaster]

Im not insulted at all, I figured it had to be something dumb I was doing.

Its a plx wideband, in the HPT help it said the voltage offset was already there you just had to pick the matching one in the aux section. The sensor itself is maybe 18" further back in the DP from the NB sensor. I reset the trims when I installed the WB and the scan I posted is after about a day of driving to allow the trims to re-learn. There are STFT's they are also negative very close to the same value of the LTFT's.

[johnh]

Your NB reading should fluctuate all over the number of time it goes rich/lean (crosscount) tells the PCM whether it should add/remove fuel.

Is there a cat between the NB and WB (you mentioned 18" apart)?

[damojo2003]

I am kinda in the same boat, but when I go WOT and I check my scan later everything is pretty much the same. While my narrow band fuel trims during cruise are close to 0, the WB reads about .2 richer.

[GTPDisaster]

No there isnt a cat between them. The first sensor,NB, is in the stock location on top of the exhaust manifold, the WB is at the bottom of the DP before the cat.

I understand that the NB flucuates but its readings on average and my fuel trims on average dont agree with what the WB is saying..... if I am reading it correctly.

At one point both my LTFT and STFT are at around -3 or so, not a big deal but indicates a richer condition, at that same point my WB is sayin AFR is around 15 indicating a leaner condition. I know the numbers arent bad -3 isnt really anything to complain about and most of my WB readings are between 14.7-15 not too far off. The thing that I dont understand is why they dont match?
If the trims are pulling fuel because the AFR is rich shouldnt the WB be <14.7? Or in another way, if the AFR is 15 shoulding the trims be positive?

[domestic rice]

You ever figure this out?

[djcushing]

Since the NB sensors aren't the most accurate things in the world, couldn't you dial them in on the Engine>Fuel>Open&Closed Loop>O2 Rich/Lean vs Airflow tables. If the WB shows lean, increase the mV in the given bank and airflow mode untill the WB reads stoich. If its rich, lower mV. Doing this should dial in the NB, right?

If the pcm thinks stoich is 450mv, it will trim untill its averaging 450mv, even if 450mv is actually 15.0 on the WB. Does this seem right?

[nitrouspaul]

glad to see people have resurected tis issue. I also have a plx and the same problem, wide band reads 15.7-16 and i am -2to3 on my stft.

dont know which way to chase my tail right now.

[5_Liter_Eater]

The narrow bands and fuel trims are going to do their best to keep the AFR at stoich. You should set up a histo to show the average AFR of the wide band when in closed loop, because without this you're just kind of guessing at what the AFR really is as it bounces back and forth.

But net net, if the wide band is showing lean in closed loop there is likely an air leak between the narrow band sensor and wide band sensor, most likely at the bung that was welded for the wide band.

[domestic rice]

I checked for leaks and no go. Just said fawk the nb02's. Shut them off and car runs great now. Some have said some cars just won't run right with the NB because they dont respond quick enough. All my problems were gone when i started running O/L. Very glad to be in a no emissions state!