maf transfer curve

[Yves]

In between 2 things I have been trying to see if based on some scatterplots in mlv I could deduct a maf transfer curve. To note is that this is for a GM LS1 maf so a frequency maf.

I made a custom field based on fuel flow which is the following : (((fuel flow in cc/min)/60) * 0.75) * AFR Target 1

The formula basically converts the fuel flow in cc/min to cc/sec and gr/sec fuel flow and then to the gr/sec of air which is needed to reach the afr target.

However when plotting this on a scatterplot vs frequency of the maf it would seem that for the same frequency I get several g/s values. Not sure how to interpret this. I would have thought that one frequency has only one possible g/s of air possible.

[Laminar]

Out of curiosity, I graphed fuel flow (cc/min) vs. pulsewidth vs. fuel pressure in MLV. It looks to me like fuel flow has some damping applied that would reduce its usefulness in determining immediate values. Perhaps you could derive fuel flow yourself based on immediate fuel flow and PW.

Also, my initial impression is that you would use actual AFR, not AFR target. To find out the actual air through the engine, it would make sense to use the actual AFR and not just the intended AFR.

I'm in a similar situation - I'm using SD but I have a MAF wired up and am curious to see if there's a way to derive a decent curve.

[Yves]

Your remarks are valid and I also tried the actual AFR. However I do not get a graph that make is possible to relate one value to one frequency. Not sure how that's possible but other more knowledgeable people may chime in.

[subwoofer]

Unless you are actually using the MAF for fuelling, the plot will be sensitive to the quality of the VE table. If that is off by any small fraction, you will get scatter. Also, EGO will give the same outcome unless you compensate for it.

[Yves]

Yes, there is scatter.

I'm a bit weary to run on maf completly on the first try, especially since I'm not sure how big of an influence reversion has/will have.

I was hoping at least to get the maf transfer dialed in as close as possible in order to have something that would be at least driveable on maf. Yesterday I have been trying several things in megalogviewer and managed to get a better result. This time I went at it with a different approach in the sense that I used pw, the fuel flow of the injectors, dead time (as measured by testing) and then calculated the gr/s of fuel that the ecu commands. I then multiplied this with the AFR ratio I'm getting through the widebands and then multiplied this times the intake pulses. This gave a result that was closely simulating the maf value (g/s) based on the current transfer curve. What I can see is that the values start to spread when the airflow increases. So this could be correct as this is the area in the scatter plots where the dots are all over the graph.

I cannot use my logs very well since I have some interference in the signal (at least that's what I think it is). Meanwhile I have made changes and hope this will yield better results.

I'm not sure a log will display the calculated value...I will post what I have with the fluctuating maf at higher tps.

[Yves]

Attached log.

I'm afraid it's not useable.

[ol boy]

I saw in TS a calculated MAF value. TS might solve the air flow number for you already.

I used duty cycle X total flow rate. 10% X 640 = 64 lbs/hr. 64 X 454 grams/lbs = 29056 grams/hr. Divide by 3600 to vet to seconds is 8.07 g/s of fuel flow. Times an AFR of 14 to 1 eguals 113g/s of airflow.

[Yves]

unfortunately I was not able to get it to work. The signal is fluctuating a lot from a tp of greater than 12 due to either resonance or reversion.

[ol boy]

Okay. My signal was noisy too. I added a 100uF cap which helped smooth stuff out.

[Yves]

I suppose that was a voltage maf...I use a frequency maf.