Choose the measurement method
S4Wiki uses ME7Logger and VisualME7Logger for detailed signal logging, and VCDS for fault codes, fuel-trim checks and misfire information. Its ECUxPlot reference covers plotting and comparison. These roles complement one another: a diagnostic block and a high-rate internal-variable log may expose different quantities and sampling behaviour.
Logging configuration is software-specific. Retain the .ecu configuration, channel-list revision, scaling and units with the log. Match variables to the examined software rather than copying a RAM address from a similarly named ECU. Connection-init examples are in the ME7.1 and ME7.5 branches.
Build a question-led channel list
The identifiers below are examples used in the cited ME7 discussion. Availability, suffixes, addresses and scaling depend on the ECU configuration.
| Question | Example signals | How to read them |
|---|
| What operating point was tested? | nmot / nmot_w, wped_w, tans, tmot, pu_w | Engine speed, pedal, temperatures and ambient pressure establish the context |
| Was the load request limited? | rlsol_w, rlmax_w, rl_w | Compare requested, maximum permitted and actual/modelled cylinder charge |
| Does estimated airflow make sense? | mshfm_w and the applicable load/manifold-model signals | Relate measured air mass to the load and pressure model |
| Which pressure is being requested or observed? | plsol_w, pssol_w, ps_w and the pressure-sensor signal | Identify upstream versus manifold pressure and calculated versus sensor-derived values |
| What did boost control command? | ldtvr_w, ldtv, ldimx and available I-adaptation channels | Separate the regulator result, post-linearisation duty and limits/adaptation |
| Which mixture path is active? | lamfa_w, lambts_w and the available final-lambda request | Follow enrichment selection before judging delivered mixture |
| What mixture correction is active? | fr_w, fra_w and available additive adaptation channels | Distinguish immediate feedback from learned correction and identify each bank |
| Why did ignition or torque change? | dwkrz, mifa, mimax, mibas, miszul, mizsolv where defined | Consider knock and permitted torque alongside ignition demand |
Pressure and lambda comparisons
Record whether pressure is absolute or relative to ambient, and whether it is upstream or downstream of the throttle. Requested upstream boost and modelled manifold pressure are not identical quantities. A disagreement can come from different measurement locations, throttle pressure drop, model errors or sensor/definition problems.
Identify the final requested lambda and the sensor used to assess actual mixture. Account for transport and logging delay when comparing an external wideband trace with ECU signals. A narrowband switching signal is useful around stoichiometric operation; establish a suitable measurement method for richer operation on that application.
Read the active limitation
- Establish the operating point and whether the ECU is in normal control, a protection state or a fault fallback.
- Compare the driver’s request with the permitted torque/load and the resulting pressure request.
- Compare that request with the pressure response and wastegate command.
- Inspect adaptations and intervention signals when the response changes between runs.
- Relate fault codes to the actual software’s diagnostic function, then inspect the implicated hardware and signals.
An ECU can reduce permitted load, retard ignition, close the throttle or enter a fallback for different reasons. The visible symptom alone does not identify the cause. Likewise, a diagnostic description containing “overboost” must be interpreted in its software context; the source documents different code assignments between S4 and 1.8T files.
Make comparisons repeatable
Keep the software/image identity, hardware state, fuel, ambient conditions and relevant temperatures with each run. Use consistent operating conditions when comparing revisions, while also checking the range of conditions the car encounters. Retain the unprocessed log as well as plots and state the units and any filtering or alignment applied.
Variant connection references
Read ME7.1 S4 logging and hardware configuration and ME7.5 1.8T logging and diagnostic code context for the source’s concrete connection settings and diagnostic-code distinctions.
Source context and adaptation
Adapted, paraphrased and reorganised from S4Wiki contributors’ Tuning, revision 5324, under Creative Commons Attribution 4.0 International. This wiki adds scope labels, cross-links and interpretation notes. The cited software observations have not been independently reproduced by this wiki.
Source sections: Logging utilities, Connection modes, Boost control DTCs, Torque monitoring.
Sources
Curated reference notes. Applicability follows the cited sources; hardware testing by this wiki is not implied.