BLM AKA long term fuel trim

[Asho88]

I was just looking to compare the A/f that the engine is running at in the log vs what it’s targeting. Could I grab a link to the comparison table mentioned in the how to I can find it on here. Cheers

[antus]

Ive not used the guide, but I just opened it to try and understand the question. I see 3 histograms mentioned and they are all there in the 12P ADX, when you look at the histograms. I don't think there is anything else. I still use monitor view and overlay target afr and wideband afr (making sure the scale is the same) and sometimes overlay CalcVE myself.

[Asho88]

I may be misunderstanding what he’s saying. When I last tuned I did a comparison of the difference between target AFR and actual AFR cell by cell and that was a painful though looking through my current log I can only see to 2 really spots so far which I think might be AE enrichment as it’s just one cell and I believe it’s happening when I put the foot into it can hear it miss and the log is showing super rich.

[antus]

Ahh I see thankyou. I read the text and did some searching and found it here: viewtopic.php?p=73155#p73155

[Asho88]

Awesome thank you. Will have a look and see if I can figure it out when I get a moment much appreciated.

[vlad01]

Regarding the BLMs, If this is 12P, BLMs with the default settings do not work. None of the factory cars prior to VS have functional BLMs I found. The Km/h reference default setting appears to be broken, to get the BLMs to work you need to switch to RPM reference.

With tuning using BLMs, I think they use a % of the VE? So if the BLM is say settled on 104, then it is compensating by adding 4% to the fueling. So if it is the VE, one could just subtract 4% to the corresponding area on the VE table, how to tell which BLM is where?, not sure but one can just watch the trace over the VE table while noting the BLM value.

[antus]

Yep thats how you do it, with a histogram. The BLM table is much much lower resolution than the VE, but you can scale and smooth it. It's something if you don't have a wideband, but using wideband data is much better than BLMs, both because of the higher resolution of the input data as well as the wider range of the sensor versus just a narrowband o2.