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Help with re-calibrating MAF sensor for Uprev

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Hi. I have fitted a new air intake system using the stock MAF sensor on a Nissan engine (vk45de), tuning with Uprev software. The engine is now running a bit lean (ECU is registering some knock and retarding the timing too) and I assume that the MAF sensor needs to be re-calibrated for the intake as it is more air is passing than it was set for.

I have done some logging and it is maxing out at about 4.25v and I have a table I can edit (see attached pic) but I have no idea what these numbers mean or how to interpret them. I understand the voltage 0 to 5, but not what the data word means. I was told once before that it is related to Kilos per hour, but thats gone over my head.

But I am at a loss on how to work out how much air is getting in and how to adjust the MAF table. At 6400rpm when the MAf is reading 4.25v that engine should be pulling in 508cfm or 14.3m3/min but what that is in Uprev dataword column I have no idea.

Any help or pointers to some info would be appreciated, thanks

Attached Files

It is pretty straight forward. Basically log MAF Voltage, MAF g/sec and adjust the MAF table accordingly in percentage changes.

To make things a bit easier you can set your A/F target table to one single value accross the map, so that the ECU targets a single A/F ratio. Once your MAF table is dailed in, you can simply revert back to your sensible A/F target table and the ECU should track the A/F values properly.

If you look into your UpRev install folder, there should be a PDF document named "UpRev Nissan Tuning Guide". Read that and it all makes more sense ;)

Thanks for the reply, It might sound simple but I am still confused. air g/sec, where could I find that information for a MAF sensor, and how many g/sec is 40215 on the table? Can I calculate the g/sec through knowing RPM and cylinder volume?

As usual I find i didn't properly explain what happened, I took the stock MAF and put it in a larger diameter intake pipe. So it is having a lower percentage of the intake air pass through it. In the stock intake it might have had (I am making these numbers up for the explanation) 3% of the intake air pass over it, and now is getting 2.5%. But I don't know exactly how much change there has been.

I think I have it sorted, I set the AFR to 12.3 across the table and adjusted the fuel compensation until O2 sensors were reading about 12.3. This was 12.5% increase, I then multiplied the values in my MAF table by 1.125, reset my tables and logged, it seems pretty close.

You need to calculate the cross sectional area of the old and new MAF tubes and express the difference as a percentage. Let's say your new MAF tube is 15% larger in cross sectional area then start by multiplying your MAF calibration by 1.15. That won't be perfect but it will get you in the ball park and you can then use your fuel trims and/or commanded vs measured AFR to fine tune.

NOTE: It's cross sectional area, NOT diameter that you need to factor in.

ok, thanks, that gives me 17% more area, why in your example did you start by adding 10% when your tube was 15% larger, was it a typo?

That was a typo. Was short on coffee. I've amended the original post :)