Whenever we are thinking engine tuning generally people think that the engine tuning is done for better speed and acceleration. With the start of the modern engine ECU we now also have the choice of tuning engines to give better fuel efficiency. Tuning engines to improve MPG is speedily becoming one of the most common forms of ECU remaps done in the UK today

Expected gains after an ECU remap for economy
Diesel engines act in response far better to ECU remapping in part because of the wider range of limits imposed by manufacturers to meet up global markets that are not forced on modern petrol engines.

  • MPG increased by 12% – 20%
  • More torque (pulling power) at lower RPM
  • Extra responsive throttle
  • Beter overall driving experience.

Engine Control Unit 2

How ECU Remapping can improve MPG
We remap the ECU to increase torque by up to 40%. We then modify where within the engine rev range this torque is made available, in the case of fuel efficiency we make it available at lower engine RPM’s. This enables you to change in to a higher gear earlier without shuddering or stalling the engine. In technical terms we not only boost the amount of torque available, but we broaden the range of engine RPM where this torque is available.


A practical example of ECU Remapping saving fuel
Think that prior to ECU remapping you needed to depress your accelerator 2 inches when in 4th gear to reach a speed of 40 miles per hour. After ECU remapping you now only have to depress your accelerator just over 1 inch while in 4th gear to reach the same speed and as we all know the less you depress your accelerator the less fuel you will use.

Let’s take this one step further. When getting to 40 MPH from a standing position you will have changed up through the gears, changing up one gear as the engine revs (engine torque) allows. After ECU remapping for improved fuel economy you can now change to a higher gear earlier and in doing so your accelerator is not depressed as much as it was prior to your ECU remap.

After having your engine’s ECU remapped for fuel economy you simply learn to change your gear changing habits and depress your accelerator less to drive in the same style as you always have. In general effect is that you will use less fuel.

At the core of the car is a box called the Engine Control Unit or ECU.
It’s generally a rectangular box situated under the glove compartment of wires trailing from it. The function of the ECU is to control the “quantity of fuel, ignition timing and other parameters by monitoring the engine through sensors.”

ECUs replaced the older carburetor, a mechanical answer to delivering an optimal air-fuel load and after 1995 most engines were running with ECU units with Electronic Fuel Injection (EFI).

Fuel injection: The ECU controls the EFI in sending a set amount of fuel into the engine. This is depending on conditions sent back to the ECU by sensors such as oxygen quantity, throttle open or close, engine temperature, vacuum, etc.

Modern ECUs incorporate a microprocessor in the system. A car generally has an ECU factory-programmed to deliver the optimal, but not necessarily the most fuel-saving mix to the car’s internal combustion engine.

This “stochiometric” or balance of air-fuel mix is usually set at 14.7:1 for gasoline engines. This means 14.7 parts air to 1 part fuel. Leaner mixtures can be achieved as high as 50:1 or even 100:1, mixing gasoline with alternative fuels such as Brown’s Gas also known as HHO.

Ignition timing: The ECU controls when the spark plugs will ignite the fuel. If it senses a bang in the engine and determines that it is caused by too early in ignition from the spark plug, it can regulate and delay the timing.

Idle control: For better fuel economy, the engine can control the rpm (revolutions per minute) of the car to save gas during idle, depending on some other systems still operational similar to air conditioning. At best cars still waste about ½ mile of fuel per minute on idle.

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