Identify the data before calculating a correction
This is shared guidance for MS41–MS45; map names and implementation belong to their ECU pages. Record injector part number, fuel, measured flow basis, differential fuel pressure, latency data and minimum useful pulse information. Compare both injectors on the same pressure and test-fluid basis.
MS4X’s injector reference separates voltage-dependent dead time from minimum injection time, provides pressure-qualified data and flags erroneous conversions in older definitions. It also notes that a voltage axis may be shared with coil dwell tables. Treat a definition-axis edit as a possible change to several functions. MS4X reference.
A worked scaling example
As an illustrative calculation, replacing a 300 cm³/min injector with a 600 cm³/min injector at the same differential pressure gives a flow ratio of 300 / 600 = 0.5. In the ideal linear region, the fuel-delivering portion of the pulse would halve. This arithmetic supplies an initial hypothesis; it does not calculate the new injector’s electrical latency, nonlinear behaviour or minimum stable delivery.
Keep dimensional quantities separate from multipliers. A value in milliseconds, a fuel-mass value, a lambda target and a dimensionless warm-up factor cannot all receive the same correction. MS41–MS43 and MS45 therefore have separate guides below.
Available cycle time
For a four-stroke cycle, two crank revolutions take 120000 / RPM milliseconds. At 6000 rpm that is 20 ms. A 16 ms energized pulse occupies 80% of that cycle. This is a cycle-occupancy example, not a universal injection-window or duty-cycle limit. Use the actual injection strategy and reported signal definition when interpreting a log.
Suggested validation sequence
- Establish mechanical condition and fuel delivery before using calibration changes to explain an error.
- Check hot idle and low pulse widths, then different electrical loads and temperatures; these can help distinguish latency errors from broad flow errors.
- Keep per-bank feedback and learned corrections in the record. Note whether adaptations were retained, cleared or still learning.
- Compare requested lambda with a suitable measured value in the state being tuned. Record sensor readiness and the feedback mode.
- Extend the evaluated range progressively and retain injector headroom. A percentage correction cannot restore missing fuel pressure or sensor range.
Use MS41 calibration maps, MS42/MS43 fuel and camshaft control or MS45 fuel mass and injector calibration for controller-specific parameters.
Sources and scope
Original reference notes by Tuning Wiki, informed by the linked MS4X Wiki pages. MS4X Wiki contributors and the authors credited by each linked project remain the source authors. Sources checked 10 November 2026. Suggested validation steps and worked arithmetic are editorial guidance; they are not a tested calibration or a claim of hardware verification.
- Fuel Injector Deadtimes (revision 23024).