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sbrunthaler
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Last seen: 2 weeks 5 days ago
Joined: 06/16/2014 - 09:48
O2 feedback and fuel map tuning question

Hi,

after doing a little research, I could not find an answer to my question. Maybe I missed some coneptual info, but I here is my question:

As far as I understand, the EMS2 used the fuel map for open loop fuel delivery and the O2FB map for closed loop operation when activated. I am using "speed density" and only 1 O2WB sensor right after the (3sx) downpipe.

On my car (3000GT VR4) with larger turbos (19T compressor) and larger SMIC's (HKS) and larger SMIC piping (CXRacing), I have to tune the fuel map richer in some areas than the (default) O2FB map, otherwise the engine won't run smoothly (RPM around 2000, load below atmosphere). This does not concern acceleration, just constant load. The difference is so big that the O2FB can't dial in the AFR from the O2FB map (lean out max = 5%).

On the other hand, the O2FB map has large areas with the same AFR value, but the corresponding cells in the fuel map have fine adjusted individueal values. If I leave the O2FB map "as-is", alle the fine tuning will go away in closed-loop mode? Is that intended?

So: Should I modify the O2FB map to match the AFR from the fuel map? Or is there something else that is wrong in my setup? Are there any concepts I am missing?

Thanks in advance for any hints,

Stefan

AEM_NS
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Last seen: 1 year 4 months ago
Joined: 06/06/2014 - 09:31
Yeah I think you're missing

Yeah I think you're missing the fact that YOU set the target values in the O2 FB Target table to whatever you want.  You tune the fuel map to get you the AFRs you want and then use the O2 FB Target table to get feedback to keep those same AFRs.  It's normal to tune an engine for "what it wants" whether it be rich or lean or whatever but it doesn't make any sense to then NOT adjust your FB targets to match the actual AFRs you're running.  FB is going to adjust injector pulse to get you whatever your target AFR is in the table so if your target is something other than what youv'e tuned for, you're not going to get what you tuned for - you're going to get what you told FB to target.  

I think you're also missing the fact that just because you're targeting the same AFR across different loads and rpms means you'll some how need the same injector pulse width value across all those cells of the fuel map.  That's not true at all.  You could target 12.0:1 everywhere - idle, low load, high load, etc - and you'd have different values in every cell of the fuel map even though you're target the same AFR all the time.

sbrunthaler
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Last seen: 2 weeks 5 days ago
Joined: 06/16/2014 - 09:48
Thank you, now I know the way

Thank you, now I know the way to go. Previous discussions with other "Tuners" confused me, but what you say absolutely makes sense.

Best regards,

Stefan