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

#af3 can cause issues manily due to a lot of headers put the rear 02 sensor in a long tube and sensor doesnt sit ig gass flow so it reads incorrectly, like whwn using an 02 spacer in rear 02, but lot of headers have a similar spacer.



they are not defined in the supplied oft tables


but if you use the ones linked below they have #af3 tavles defined




https://www.ft86club.com/forums/showthread.php?t=126180

Improved AFR
 

This is quite after the fact as the summer was a busy one.
I was able to attenuate the lean AFR pockets I observed previously by doing this:
1) putting more voltage reference points in the 3-4V range of the MAF Sensor Scaling table and rescaling the MAF,
2) modifying the Engine Load Compensation table.
I did a few 2nd gear pulls and the results are shown in this graph. AFR is still not perfect but good enough to my liking. The engine loads on the other hand tell me that the AVCS tables need improvement.

I started to get some pretty wild fluctuations in my commanded AFR and AFR after reverting back to factory, then reinstalling long tube header. Switching out the O2 sensor doesn't seem to effect it. It would still have these fluctuations even with brand new O2 sensors.



This behavior seems to effect the idle as well at times, causing the rpm to dip and engine to cut off. What would cause the commanded AFR behave this way if it was not a faulty O2 sensor? Misfires? Exhaust leak at the headers? Has anyone seen this kind of thing before?



https://datazap.me/u/solidone/afr-fl...8076&mark=7744




https://datazap.me/u/solidone/afr-fl...7616&mark=7744

disable the useless secondary o2 sensor by zero'ing the 2 af#3 tables

The thing is, I think this was happening even with a complete revert to stock including the original factory tune. Something is definitely not working normally. I was hoping it was the downstream O2 when I couldn't find a vacuum or exhaust leak, but unfortunately it behaved relatively the same when I swapped it out.



I suppose I can give that a try and see if it changes anything.

I zeroed out the AF #3 limits (CL Target compensation Limits, Correction Limits, Learning Limits), the idle no longer dips and I havent had the engine cut off coming to a stop, but I still have this odd condition where the commanded afr hangs at 15.06 during part throttle operation. It seems to happen mostly right when the engine load comes to 0.8. Before the load hits 0.8 or as soon as it goes past 0.9-1.0 engine loads, the commanded afr seems to work fine. Very strange. I'm still suspecting an exhaust leak (header gasket or small crack in headers?), but I'm not so sure that would explain the behavior in commanded AFR?



https://datazap.me/u/solidone/log-16...3888-8330-8346

Spoke too soon... stalled three times in a row coming to a stop. Then three time the idle dipped (progressively less prodounced), then back to normal again...


https://datazap.me/u/solidone/stall-...3370-4828-5854


@steve99 @Kodename47 you all have any idea? :iono:

Increase the values in the overun fuel resume tables say 200 rpm at the bottom end

I will try that, but its doing the same thing with completely oem hardware and the original factory A01C rom.


This issue popped up right after I reverted back to stock for smog check, and stayed this way after reverting back to the previous setup minus the flex fuel. I did not reinstall the oil cooler or flex fuel system. With the long tube header, with this tune the closed loop fueling was pretty dead on, but now it run rich into the 11's:1 afr going high and wide open throttle. As well as this dip and stalling and the commanded afr issue. Same exact intake and exhaust set up.

Hey @solidONE, did you resolve this?

I am noticing that AFRs are doing something similar cruising at lower loads:

https://datazap.me/u/cjwalther/16nov...4-6&zoom=5-583

I'm also A01C, running stock intake, but just threw on a ptuning 4-1.

Last post was from last year.
Last Activity: 09-24-2021 01:09 PM
:search:

Go to someone in here that's still active.

did u try zero'ing af#3 trims?