AFR Command Fluctuations
 

Hi, I am looking for insight on some weird AFR Command behavior I observed in a data log. I recently installed a JDL 4-2-1 catless header, and flashed the OFT v4.03 Stage 2+ tune. The only changes I made to the rom file were in the drive-by-wire maps. My car is all stock, except for the header.

The data I show as an example in the figure is in closed loop, and the horizontal line on the MAF Voltage plot marks the LTFT switching from Range C to Range D (above 20 g/s). It looks to me like the AFR Command is somewhat erratic, which causes the STFT to chase a proper trim, and therefore causing the actual AFR to fluctuate too.

Does anyone have an idea on what is going on? Thanks for any help on this!

Is the car on O2 sensors fully warmed up?



I recall a a long while ago I was having irregularities in my commanded afr. Somehow I decided to change out the downstream O2 sensor. I forgot the reasoning. Though, after I did that the issue resolved. This was in between switching out and testing different catless headers and front pipes.

probably just the CL target that swing between 14.7 (when you release throttle in overrun) to low 14
+ the o2 secondary lambda which I usually disable
Should be ok anyway

I started logging 7-8 minutes after starting the car and driving so I assume the sensors were warmed up. I was not aware that the downstream O2 sensor played a role in closed loop fueling since my rom definition file does hot have tables for it. I just found out in another thread that these are the "A/F #3 Correction" tables, which I assume is what you are referring to.

Now that I think of it I had a hard time unscrewing and re-installing that sensor onto the new header. Maybe the threads were damaged and there is a leak. I hope I did not damage the threads on the JDL header. I will order a new Denso sensor and see whether that fixes my problem.

Are you seeing fluctuations under both closed loop and open loop operation? Ex. Does the Commanded AFR not follow the targeted AFR consistently under full throttle? If it runs fine and you are not seeing changes in you fuel consumption, its probably not a big deal. But if you messed up the threads on the O2 sensor and there is a leak, then you should address that.

it won't fix the problem, because it's not a problem. it's the correction actuated by it, it works only on closed loop around 14.7
i usually disable the 2 A/F#3 table so that goes away

The downstream shouldn't* have an effect in open loop, but you might get some weirdness if it's behaving sluggish. I found some old WOT logs when this was going on prior to changing out the downstream. I was also beating the shit out of it testing and taking these logs, which might have contributed.


Goes to 15.06 Commanded momentarily when I open the throttle:
https://datazap.me/u/solidone/plm-st...2676&mark=2551


This is soon after changing it out. (If I remembered correctly, this was in 2015)
https://datazap.me/u/solidone/catles...1997&mark=1881

another reason to disable it

Something something fuel economy at low loads. lol That was my 'logic' when that was suggested by Kodename47

Unfortunately for now I can't disable the A/F#3 tables because they are not defined in OFTv4_ZA1JF00C.xml . Until I find a workaround and update my rom I will log open-loop runs as suggested by @solidONE to check that everything is normal at high loads. I had not done it yet because I was driving cautiously just in case my car indeed had an issue.

A follow-up on this thread. I haven’t done WOT pulls yet because I have noticed consistent lean AFR pockets at 3550 rpm during spirited driving. I think it has to do with excessive scavenging and fresh air making its way to the A/F sensor. I will have to tweak the AVCS tables.
Note: the high AFR Command on the figure is due to erroneous logging in open loop below 4200 rpm.

Why not just correct the fuelling?

Also how is the commanded AFR logging incorrectly but the O2 sensor logging OK?

I hypothesized that since at these rpms and loads fuelling is in direct injection only, some fresh air was bypassing the combustion chamber through the valves without receiving the DI charge, and that was creating a false leaner reading on the sensor. But if this is not the case then I could indeed modify the open loop fuelling tables.

Now for the commanded AFR incorrect logging I have no idea what is going on. I just assumed it was an OFT glitch.

Any update here ?? pse