Torque, load and pressure are different quantities
The pedal enters a torque-oriented control system. The ECU uses models and calibration to relate a permitted torque request to cylinder charge or load. Turbocharged applications then use the pressure and air-path model to produce the required charge. A load value is not the same as pedal position, throttle angle or gauge boost.
Relative torque and relative load use different normalisations. In the cited ME7 strategy, load can exceed 100%, while the torque percentages have their own reference. Retain the quantity, units and axis meaning beside each map.
Read the request and limit chain
| Function or map | Role described in the source | Question to ask |
|---|
| KFPED | Pedal and engine-speed contribution to requested relative torque | How is driver demand scaled at this operating point? |
| KFMIRL | Torque-request to requested-load relationship | Does the requested torque map into the intended charge? |
| KFMIOP | Load-to-relative-torque relationship used in torque modelling and request scaling | Are the torque estimate, permitted request and inverse relationship coherent? |
| LDRXN | Maximum specified-load contribution | Is the load ceiling limiting the request? |
| KFLDHBN | Requested pressure-ratio limitation and its load equivalent | Is turbo/pressure-ratio protection more restrictive? |
| KFTARX and associated corrections | Temperature-dependent influence on permitted load | How does the request change with intake temperature? |
| Torque monitoring and interventions | Checks and limits acting on the permitted torque path | Did the ECU reduce the request or change ignition to enforce a limit? |
There is no single boost table that explains the entire system. Raising one candidate ceiling does not force the final requested load to rise if another constraint or the request conversion is more restrictive. Trace the request into the active limit, then into the pressure request before changing the feedback controller.
S4Wiki gives a detailed M-box calculation with particular loss-torque, efficiency and manifold-model terms. That worked relationship belongs in ME7.1 S4 load torque and ignition examples rather than being asserted as identical code in every ME7 application.
Use consistent pressure references
Absolute pressure includes ambient pressure. Gauge pressure is the difference from ambient at the reference location. For example, 2000 mbar absolute at 1000 mbar ambient corresponds to 1000 mbar gauge. This is a unit illustration, not a calibration target.
The source distinguishes requested manifold pressure from requested pressure upstream of the throttle. Temperature, cylinder filling, residual gas and pressure loss influence that conversion. Establish which sensor or model produced a logged value before comparing it with a request.
Targets and boost-control response
The controller reacts to the difference between the relevant requested and actual pressure. Its proportional, integral and derivative contributions have different roles, and the applicable strategy can schedule or limit them by operating state.
| Calibration | Control role in the source | Useful observation |
|---|
| KFLDIMX | Integral-regulator limit | Whether the integral term is constrained and how steady response follows the limit |
| LDIATA | Temperature-related contribution to the integral limit | How available command changes with intake temperature |
| KFLDRL | Post-regulator wastegate-duty linearisation | The relationship between regulator output, final duty and achieved pressure |
| I-regulation adaptation | Learned correction to regulator behaviour | Whether the command changes over repeated runs or conditions |
| Protection and diagnosis | Over/under-pressure checks, load reduction and fallback | The active diagnostic function, timer and resulting control state |
Use wastegate and turbo hardware that behaves consistently before trying to explain a response through map values alone. Inspect hoses, charge-air leaks, actuator behaviour, N75 operation and the system’s achievable flow. The source describes the integral limit as important to the documented system’s sustained response, with KFLDRL shaping the final duty.
Observe the regulator output and final duty separately when those channels are available. A change in the post-linearisation map changes how a given regulator result drives the hardware; it does not itself define the desired load. Temperature and altitude corrections and learned adaptations can also explain why identical-looking requests produce different duty traces.
Diagnose intervention before raising limits
Compare requested load, permitted load, actual/modelled load, requested pressure, actual pressure, duty and adaptations. If the request itself falls, inspect the request/limit path. If the target remains high while pressure cannot follow, inspect hardware capability, control response and fault state. If timing changes at the same moment, examine torque intervention and knock information.
Keep torque-monitoring calibration coherent with the torque model. A load-axis change can affect other maps sharing that axis; the source’s M-box examples explicitly link KFMIOP axes with optimal-ignition and other torque functions. Raising a diagnostic threshold alone does not explain or correct the original deviation.
Respect the represented operating range
A sensor, its conversion, internal pressure or load representation and a table axis can each impose a separate range. A saturated model or sensor can stop the ECU observing the error needed by the controller. The M-box notes contain the source’s concrete pressure-range example; extended-range software must be documented with its exact changes.
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: Boost, Requested boost and load, Boost PID, Torque monitoring.
Sources
Curated reference notes. Applicability follows the cited sources; hardware testing by this wiki is not implied.