Decoding the MS42: Deep Dive into the BMW Engine Control Unit

The Siemens Ms42 engine control unit (ECU) is the brain behind the BMW M52TU inline-six engine. This sophisticated system relies on an Infineon C167CR_SR CPU running at 20MHz and 4 megabits of AMD AM29F400BB flash memory to manage and optimize engine performance. Understanding the intricacies of the MS42 is crucial for tuning and diagnostics. This article delves into the core components, memory layout, checksums, and key features of the MS42 ECU.

MS42 Memory Architecture: Bootloader, Code, and Calibration

The MS42’s memory is organized into three primary sections:

Bootloader (00000 – 0FFFF): This 64kB section is critical for ECU initialization. It contains interrupt routines, I/O configurations, immobilizer data, and user information fields (UIF). The bootloader is typically one-time programmable, meaning changes are irreversible under normal operation. Specialized tools like JMGarage Flasher are required for modifying the bootloader, usually for tasks like ECU virginizing or altering the UIF without impacting the flash counter. Modern immobilizer and checksum deletion methods often bypass the need for bootloader flashing.
Program Code (10000 – 1FFFF & 50000 – 7FFFF): The program code resides in two 192kB sections, containing the core logic for engine management.
Calibration Data (48000 – 4FFFF): This 32kB section stores essential engine parameters, constants, and lookup tables used for real-time calculations.

Checksum Verification in the MS42

The MS42 employs three CRC16 checksums to ensure data integrity:

CRC16 Type	Memory Address
Boot	0x3C24
Program	0x50306
Calibration	0x4FEE0

These checksums protect against data corruption. Disabling the calibration checksum involves modifying specific memory locations: setting the word at 0x4FEFE to 0xFFFF and the byte at 0x5002C to 0xA8.

Fueling Strategies and Modifications

The MS42 relies on engine load and speed to determine fuel injection duration. It utilizes narrowband lambda sensors for closed-loop control and incorporates learned trims that influence full-throttle fueling. Key fuel maps include basic injection time (IP_TIB), full-load enrichment (IP_TI_VL), and various temperature and VANOS-related compensation tables.

When upgrading injectors, several parameters require adjustment:

Injector Scaling: T_TIAS[0-5], ti_min_ev
Injector Latency: kf_ti_add_totz__ub
Fine-Tuning Maps: kf_ti_kstntkw, kf_ti_tkw1_vanos_llnlm, kf_ti_tkw2_vanos_llnlm, kf_ti_tkw2_vanos_tl_bk1nlm, kf_ti_tkw2_vanos_tl_bk2nlm, kf_tibnlm, kf_vti_kst__tkw
Cylinder Rewetting: kf_ti_swf_min__tkw, kf_ti_lwf_min__tkw

Ignition Timing and Control

The primary ignition timing map is kf_zw_roz98_vanos_tl__n__lm, based on airflow and engine speed for 98 RON fuel. The MS42 interpolates between 98 and 91 RON tables based on knock detection. Other timing maps address cold engine operation and catalyst heating. Exhaust popping can be achieved by modifying overrun fuel cut detection thresholds.

VANOS System Management

The MS42 controls the dual VANOS system, allowing independent adjustment of intake and exhaust camshaft timing relative to the crankshaft. This optimizes emissions, low-end torque, and high-end power. Numerous maps govern VANOS behavior based on engine temperature, load, and speed.

Diagnostic Trouble Code (DTC) Suppression

Specific DTCs can be suppressed by zeroing out corresponding epz_inc_... codes within the MS42.

Additional MS42 Features and Modifications

The MS42 offers further customization options:

E-Thermostat Temperature Adjustment: Modifying tkw_soll_toel_min, tab_tkw_soll_kfk__n__lm_ers, and tab_tkw_soll_kfk_ka__n__lm_ers allows control over coolant temperature targets.
Secondary Air Pump (SAP) Delete: Setting konf_ssp to 0 or modifying relevant maps disables the SAP.
Post-Cat O2 Sensor Delete: Setting konf_abgasanlage to 1 simulates a two pre-cat O2 sensor configuration.
Single O2 Feedback: konf_abgasanlage offers various options for lambda probe setups.
MAF Scalar Adjustments: The MS42’s MAF table can be adjusted, often in conjunction with larger MAF sensors or resistor modifications for boosted applications.
Throttle Response: Modifying KF_MDK_SOLL_PWG_TKW1 and KF_MDK_SOLL_PWG_TKW2 alters throttle response characteristics.
RPM and Vmax Limiters: Adjusting specific tables controls RPM and speed limits.
Alpha/n Mode: Disconnecting the MAF sensor forces the ECU to rely on the Alpha/n map (KF_LM_DIAG_1).

Safety Features: Misfire, Knock Detection, and Fuel Adaptation

The MS42 incorporates crucial safety features:

Misfire Detection: Parameters n_min_lu and n_max_lu define the engine speed range for misfire monitoring.
Knock Detection: tab_zw_dec_kr_1__n and tab_zw_dec_kr_2__n control ignition timing reduction in response to knock.
Injection Adaptation: n_ti_ad_fak_min and n_ti_ad_add_max govern fuel trim adaptation based on engine speed. Caution is advised when modifying these safety parameters. Disabling or altering them can lead to engine damage.

This comprehensive overview provides a foundation for understanding the complexities of the MS42 ECU. Remember to proceed with caution when modifying engine parameters and prioritize safety.