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ECU remapping

Revision 1

by llandowtuninguk@gmail.com
Publish the ECU remapping overview for the performance section.

This is a historical revision. Read the current page or return to its history.

Page organisation in this revision
Page type
Technical article
Subject
Performance
Parent
Section level
Applies to
No ECU-specific applicability
Tool groups
None
Manufacturers
None

What a remap is

A remap replaces calibration data in the engine control unit. The replacement can change how much torque or fuel is requested, how much boost is allowed, when the spark or the injection happens, and where the protective limits sit. It does not move air through a port, and it does not make a compressor larger. If the original engine was already at a limit set by airflow, knock or exhaust temperature, changing a single request often does nothing useful until that limit is understood.

The maps are not a universal list. A torque-structured petrol ECU, a quantity-structured diesel ECU and a carburettor engine are different control problems. On this wiki the worked examples are tied to particular families: ME7 torque, load and boost, ME7 fuelling and airflow, ME7 ignition and knock, EDC15 fuel quantity and EDC16 torque and fuel. Use those for the control system they describe. Do not copy a map name, a unit or an address from one of them onto another ECU.

Requests, limits and the value that is actually used

Bosch's EDC description calculates a fuel quantity and then limits it. The quantity that reaches the pump or the injectors is not automatically the driver's request. Air, engine speed, temperature, a fault or an external intervention can hold it down. The same pattern appears in later torque-based systems: a driver request is converted toward a fuel or air target, and several limits can sit underneath it. Raising one table leaves the output unchanged when another limit is lower.

That is why a remap and a hardware change have to be read together. A larger turbo, a freer inlet or a different injector changes the air or fuel the original tables assumed. The ECU may still be modelling the original engine. On an airflow-metered petrol system the sensor calibration and the load calculation have to match the air that is now flowing. On a diesel the smoke, or air, limit is there to stop fuel being injected when the air is not available. Removing the limit without the air is how smoke and exhaust temperature are made, not how reliable torque is made.

What is usually involved

  • Driver request. Pedal to torque, load or fuel quantity. This sets what the driver is asking for. It does not override a lower limit.
  • Air path. Boost target, wastegate or vane control, and the model that estimates how much air arrived. See forced induction.
  • Fuel. Injection quantity or pulse width, lambda, and the point at which the mixture is enriched for component protection. See fuel system upgrades.
  • Ignition or injection timing. Advance is useful only while the engine is not knocking and the exhaust temperature is acceptable. See ignition timing.
  • Protection. Rev limit, torque limit, temperature limits, sensor plausibility and diagnostics. A calibration that hides a real fault is not a performance calibration.

Hardware the calibration has to know about

These changes alter the air, the fuel or the knock margin. The original software does not discover them by itself.

  • A different compressor, turbine housing or boost-control actuator.
  • An intercooler that changes manifold temperature and the pressure loss, as described in charge cooling.
  • Injectors with a different flow, or a fuel that is not the one the stoich and timing tables assume.
  • A camshaft, inlet runner or exhaust that moves the torque peak. The volumetric efficiency the ECU uses is then wrong at some speeds even if the peak looks fine.
  • A change in compression ratio or displacement, which changes both the knock behaviour and any load model built from the original geometry.

A practical boundary

Keep an original file that can be restored. Identify the hardware and software numbers before comparing logs. Change one system at a time, and judge it from requested against actual boost, fuel quantity or lambda, ignition retard or knock control, and temperatures. A higher requested number that the engine does not deliver is a sign that some other limit, or the hardware, is still in the way.

Emissions equipment and the diagnostic checks around it are part of the calibration. This page does not describe how to defeat them. A road vehicle also has to remain within the law that applies where it is used.

Sources