NefMoto

Hi everyone.

I'm hoping someone can help me. I'm not new to tuning however I am new to scaling a MAF. I know there are many questions about this but please let me explain.

I normally tune Volvo's, early Volvo's using the Motronic 4.4 system. A friend of a friend has had a tune dropped on to his Vauxhall Zafira Z20LET with Motronic 1.5.5 which the tuner swears is tuned for an 80mm MAF over the stock 70mm. I find this not the case due to constant positive fuel trims when the 80mm is installed followed by a DTC and limp mode.

I have also confirmed this by reading the MLHFM MAP which is the same as a stock file.

After never scaling a MAF before I made a quick excel sheet to do the job taking into consideration MLOFS of 200.
I could have sworn recently that I read an article, maybe on this forum regarding negative numbers in the map and something needs to be done. Besides the usual subtract MLOFS, scale, then add on MLOFS again.

My main question is just that:
Does anything need to be done to the negative numbers once MLOFS has been subtracted?
My other question:
How does the ecu interpret the negative number once it subtracts MLOFS. I can understand for example 212kg/h - MLOFS = 12kg/s but how would it interpret lower figures such as 160kg/h - MLOFS = -40 kg/h ? or would the ecu just ignore these lower figures?

I have attached a copy of the excel file I put together, The file also has line charts to show the differences. Within the file I have already input the MLFHM from the ecu.

Thanks in advance.

Mike

I had a quick look at the scaling, the multiplier between 70mm and 80mm is approx 1.14
your max stock kg is 966, after removing and adding the offset I get 1073kg max.
That should be a good starting point.

The reason there is a negative MLOFS is because there is no way for the MAF to send a negative voltage, so zero flow (for a given MAF) is a represented by a small positive voltage. Below that voltage is "negative" flow

So for the scaling to work, you subtract so that that "zero" point doesn't get moved, then scale the values, then add it back so the zero voltage point still results in zero when you take MLOFS into account.

Thanks for the replies.

So would I be correct if I said I don't have to worry about the negative numbers so much? Basically still do the scaling but as long as any number returned as a postive after subtracting MLOFS, is then scaled properly then I should be good to go. After this then do the usual of tuning the correction map if required.

The reason all this has thrown me off is because on the Motronic 4.4 ECU's, the MAF is a bosch however there does not seem to be an offset and the maf scale is pulled from different parts of the ecu. When converted it starts off as 0's all the way to a positive flow then the numbers start increasing. (Info/scaling is in the attached file-Main post)

I suppose the main answer here especially for M1.5.5 is to perform the usual scaling equasion and I should be ok.

The HFM-2 (or earlier) that is used on Motronic 4.4 does not have reverse flow measuring capability.

If MLOFS is zero then adding/subtracting MLOFS is a NOP :P