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REV limiter - Diesel

ECM Titanium Tuning Tips

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REV limiter - Diesel

ECM Titanium Tuning Tips

Modifications to ECU parameters that produce special effects aren’t exclusive to petrol engines. Turbo diesel engines can also deliver a thrilling performance! Known for their durability and fuel efficiency, these engines were widely used by car manufacturers, especially in the early 2000s. This widespread adoption has led to a large community of enthusiasts who customize their vehicles through various ECU optimizations, including the activation of the REV limiter, which enhances the vehicle’s sound with a more aggressive tone.

For diesel engines, where it’s not possible to cut ignition (unlike petrol engines with spark plugs), the REV limiter is achieved by sharply cutting off fuel injection at a specific RPM. This results in a sudden drop in engine speed, followed by a quick rise, creating the desired sound effect.

How is the modification achieved?

To activate the REV limiter on a diesel engine, adjustments need to be made to several ECU parameters, depending on the desired effect, including:

  • Amount of injected fuel
  • Fuel limitation
  • Torque limitation
  • Injection timing
  • RPM limiter

It’s important to note that there are two types of limiters: “Hard REV” and “Soft REV”.

The Hard REV, also known as the “Popcorn Limiter,” is achieved by adjusting the torque and fuel injection parameters to set the RPM at which the limiter will activate. Additionally, the injection timing maps must be adjusted to delay the injection, allowing unburned fuel to fill the combustion chamber and be expelled through the exhaust. This type of limiter is the most aggressive, creating a distinctive visual and sound effect.

The Soft REV can be configured in two ways. When available, you can use the RPM limiter maps in the ECU’s driver, which function as overspeed thresholds. Once a certain limit is exceeded, the ECU automatically cuts fuel injection to prevent engine damage. By adjusting this threshold, you can precisely define the RPM at which the fuel cut-off occurs, thus activating the limiter. Alternatively, when this option isn’t available, adjustments can be made to the fuel and torque maps. In this case, the procedure is similar to the Hard REV, but without altering the injection timing.

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Example

REV Limiter (Hard REV) on BMW 330D E92:

Thanks to the maps available in the driver for the Bosch EDC16C35 ECU, installed in several BMW diesel models, such as the 330D E92, you can precisely activate and customize the intensity of the REV limiter.

This guide will show you how to adjust the torque, fuel, and injection timing maps to achieve the desired effect. We will use ECM Titanium software for these modifications, as it allows you to:

  • Clearly visualize the useful ECU maps.
  • Make precise adjustments to torque limiters and fuel injection quantities.
  • Delay injection timing as needed.
  • Save custom configurations.

1. Torque Limiter

Torque limiter tuning: the first step involves setting the maximum torque limiter value near to zero at a specific RPM across all gears. This defines the RPM at which the limiter will activate to create the REV limiter effect.

2. Fuel Injection Quantity

Modifying fuel injection maps: similarly to the torque adjustment, you must zero the fuel injection values at a specific RPM, selected based on your needs.

3. Injection Timing

Injection Timing map adjustment: this adjustment is crucial for achieving and regulating the intensity of the Hard REV. It’s this operation that differentiates the behavior of the limiter between Hard and Soft REV.
In the injection timing map, you must set the desired RPM (the limiter RPM defined earlier) and then delay the injection. This ensures fuel is injected when the piston has already reached Top Dead Center (TDC) and is in the expansion phase.

This combination results in unburned fuel entering the exhaust, accompanied by increased gas pressure, producing the characteristic popping exhaust sound (and in extreme cases, flames).

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