BMW E36 M50 / M52 MS41.1 / MS41.3 MAF Tuning
Updated: Sep 22
MAF tuning corrects the relationship between MAF voltage and calculated airflow.
BMW MS41 uses a 12V MAF with a 0–5V signal output.
MAF Tuner
MAF Tuner combines multiple RomRaider datalogs and calculates suggested corrections to the MAF curve.
It uses fuel-trim data and, where applicable, wideband and AFR-target data to calculate MAF scaling changes.
Required Files
Keep these files in the same folder:
MS41 MAF Tuner.exe
MS41 MAF Tuning.xlsm
RomRaider CSV datalogs
Before Logging
Open the MAF Tuning spreadsheet and:
Paste in your current MAF Scaling table.
Set the minimum Hit Count required before a cell is changed.
Set the Change Effect percentage from 0–100%.
Save and close the spreadsheet.
Datalog Requirements
Collect several short datalogs from low RPM to high RPM.
Use:
Steady throttle
Multiple RPM ranges
Multiple load areas
Closed-loop operation where possible
WOT enrichment OFF while collecting correction data
The goal is to collect enough usable data to populate as much of the MAF curve as possible.
Note: To fill higher-load areas of the MAF table, use light foot-brake pressure during a long, smooth pull from the lowest usable RPM in a gear up to redline. Avoid excessive brake pressure or brake overheating.
Data Used by MAF Tuner
MAF Tuner analyzes:
Short-Term Fuel Trim
Long-Term Fuel Trim
Wideband AFR
AFR Target — MS41.3 only
Current MAF Scaling
Hit Count per cell
Correction percentage
Run MAF Tuner
After collecting your logs:
Place the CSV logs, MAF Tuner program, and spreadsheet in the same folder.
Run MS41 MAF Tuner.
The program combines the datalogs.
It calculates the MAF corrections.
The results are written into the MAF Tuning spreadsheet.
Review the Results
Review:
Average Correction %
Hit Count / Cell
Suggested MAF Scaling
Tuned MAF
Smoothed MAF
The spreadsheet can smooth the MAF curve using a best-fit calculation.
Choose either:
Tuned MAF
or
Smoothed MAF
Then copy the selected MAF table into your next RomRaider tune revision.
Repeat the Process
After flashing the corrected MAF table:
Datalog again.
Run the new logs through MAF Tuner.
Review the corrections.
Update the MAF table.
Repeat until the correction values and fuel trims are consistent.
1024 kg/hr Mode
Stock MS41 uses a MAF range of:
1024 kg/hr
This is the standard airflow range.
2048 kg/hr Mode
MS41.1 / MS41.2 can also use:
2048 kg/hr Mode
This doubles the available MAF airflow range.
When converting from 1024 kg/hr to 2048 kg/hr mode:
Divide all 256 MAF Scaling values by 2.
Example:
Original MAF Scaling ÷ 2 = Starting 2048 kg/hr MAF Scaling
Update the 2048 kg/hr MAF Scaling table before flashing the tune.
RomRaider Note
Depending on the XML definition being used, the 1024 kg/hr MAF Scaling table may appear read-only.
The MAF table definition can be moved earlier in the XML definition file if editing that table is required.
Turbocharger Warning
The stock engine-load limit remains:
1389 mg/stroke
even when using 2048 kg/hr MAF mode.
A fast-spooling turbocharger can exceed the stock load range at relatively low RPM.
This can cause incorrect fueling calculations and potentially lean AFR.
Always datalog:
Engine Load
AFR
MAF Airflow
MAF Voltage
Fuel Trims
Increasing the MAF airflow range does not increase the stock engine-load limit.
If Engine Load approaches 1389 mg/stroke, the stock MS41 load strategy is reaching its limit.
MS41.3
MS41.3 uses extended airflow and load ranges, reducing the need for the older 2048 kg/hr workaround on high-airflow setups.
MAF Tuner can also use AFR Target data on MS41.3 when calculating corrections.
Nissan / Hitachi MAF
When installing a Nissan / Hitachi MAF, wiring the sensor is only the first step.
The MAF transfer curve must also be calibrated using:
Starting MAF scaling
Fuel trims
Wideband AFR
Datalogs
MAF Tuner corrections
Related Guide: Nissan / Hitachi MAF Wiring
Important
Do not copy a MAF curve and assume the tune is complete.
Every MAF installation should be verified through datalogging and correction.
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