Fuel injection 101

Fuel injection 101

An engine is a motor which turns fuel and air into movement. The primary purpose of the map on an ECU is to control the air/fuel ratio. This is fuel injection 101.

What is fuel injection?

fuel injection injectorThe fuel injectors on a car can be opened for a specific number of milliseconds to inject measured amounts of fuel. Some can even be adjusted to spray a different pattern. This affects how quickly and completely fuel combusts inside the cylinders of the car. Injectors are manufactured by the car manufacturers themselves such as GM, or by specialists like Bosch or Lucas.

The ECU will send electrical signals to operate the fuel injectors and control the balance of:

  • Engine power
  • Fuel efficiency
  • Engine safety
  • Smooth engine running

There are lots of extra considerations like smoke control, safe operating temperatures, fuel quality, emissions and so on, but the primary goal is to control the right amount of fuel injection with the right timing. This gives maximum power from the engine without risking damage without wasting precious fuel. To begin to understand remaps one must first understand fuel injection.

What types of fuel injection are there?

  • Single point: Very similar to an old carburetor system, but with a controlled injector on the throttle body.
  • Continuous injection: Uses 1 or more injectors to provide a constant supply of fuel. The amount of fuel is varied, and the system can be entirely mechanical so no need for electronics.
  • Multipoint fuel injection: Injectors are mounted by each intake port and fired individually or in groups for even better control.
  • Direct injection: This system injects the fuel at even higher pressures directly into the combustion chamber above the piston. This means better fuel efficiency and emissions but is more costly because of the heat and pressure in the chamber. The piston and chamber surfaces can also be cooled and lubricated by the fuel.
  • Swirl injection: Fuel is sent into a swirling, rotating pattern in the chamber. This helps with fuel mixing (atomization) especially in diesels where complete fuel combustion is more challenging.


fuel injection tuningOn a standard ECU map, the car is set up to operate reliably and efficiently across a huge range of variables. A European car manufacturer must set up their vehicles to cope with the mid-day summer heat of southern Spain and the sub-zero frozen heights of the Swiss alps. It must adapt for fuel quality of crappy watered-down greek petrol or on farm-fresh juicy Italian benzin. It must adjust for cold oxygen dense air and for hot dusty dry conditions. It also has to manage good fuel economy and clean emissions!

With the right air/fuel mixture at the right time modern cars can do all of these things well. If there is too much fuel (or not enough air) the engine will not be economical and there is risk of mechanical damage to the engine and exhaust systems. If there is too little fuel the engine will suffer from low power, and again there can be mechanical damage.

Why does a remap increase power?

fuel injection pistonsVehicle manufacturers must compromise and sacrifice performance characteristics to appeal to a wide variety of customers. An enthusiast may want more power and more aggressive responses. They might be happier with a louder exhaust and engine sound. They might want the exhaust to burble, pop and bang. They might want a dump valve that goes ptsshhhhh on every gear. However a non-enthusiast may give up these characteristics for a quieter ride and better fuel efficiency.

A custom remap gives control over these compromises, if the owner accepts slightly increased risk to the engine components.