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MS42 and MS43 load reference

Measured, injection, ignition and VANOS load signals, their map-axis implications and a diagnostic workflow for MS42/MS43.

Updated by llandowtuninguk@gmail.com   Revision 2

Applies to
Siemens MS42Siemens MS43

Check the hardware and software limits stated in this article.

Scope and signal selection

This article covers MS42 and MS43. Their MS4X references distinguish maf_mes (measured), maf_ti (injection), maf_iga (ignition) and maf_ivvt (VANOS). These signals are not interchangeable map axes. MS4X reference; MS4X reference.

Follow the calculation being evaluated

QuantityDocumented distinction
Injection loadUses an intake-manifold/valve-overlap model.
Ignition loadSelects between injection load and a separately filtered airflow signal.
VANOS loadBlends measured airflow and substitute-table information.

The substitute table ip_maf_1_diag__n__tps_av participates beyond MAF fault fallback. The VO table group is ip_maf_vo_[1-8]__map__n. MS4X reference; MS4X reference.

Build a map-specific comparison

Write down the quantity, unit and filter used by each axis. For a proposed ignition-map change, ask for ignition load; for an injection-map change, ask for injection load. If the logger only exposes measured airflow, record that limitation instead of labelling it as the missing internal signal.

At a fixed RPM, two samples with identical measured airflow may still occupy different internal states. Compare temperature, camshaft position, transient direction and fault/substitute status before concluding that a table is ignored. This is a suggested diagnostic comparison, not a replacement implementation of the ECU model.

Airflow range and model range

For a modified engine, review sensor range, the model’s pressure/load axes, and the load available to fuel and ignition calculations as separate questions. Changing one scale does not demonstrate that the rest can represent the new operating region. Use the original MS4X model discussion for the equations and table relationships; retain software-specific axis definitions with each worked example.

The MS430069 extended-load reference documents a separate MS43 firmware package with its own matching files. Its support does not establish the same extension for MS42. Continue with fuel and camshaft control and data logging.

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.