Fuel Injection

How fuel injection engine works.

After the era of Carburettors, Fuel Injection systems became common in motorcycles. Fuel Injection is more of an electronic system installed in the engine. The computers in the system adjusts the fuel-air ratio digitally rather than mechanically, like in a carburettor. All this takes milliseconds to compute and the engine is ready to be switched on.

The principle is simple. Oxygen sensors in the system picks up the amount of oxygen from the exhausts and produces a voltage based on the reading. Normally, the sensors can produce voltages up to 1000mV. However, a reading above 500 is said to be a rich mixture and brings excess fuel and a reading below 500 - a lean mixture, bringing in excess of air. The computer in the system tries to make sure that the value stays at 500 or to keep the ideal stoichiometric ratio of 14.7:1 (air-fuel).

To keep the ratio stay the same way, the computer manipulates the time for which the fuel injectors operate. For example, a reading of 700mV will be picked up by the computer and sends a signal to the injectors to remain open for a time shorter than before to bring down the reading to 500. If the reading is too low, the computer directs the injectors to remain open until the desired value is obtained.

The advancement of digital technology and the use of digital algorithms to compute various inputs and the simplicity of the system itself are one of the main reasons why fuel injection has been preferred by manufacturers over the years. The carburettor is a mechanical device and has the advantage of allowing the owner to custom tune the mixture to get a smooth engine but cannot handle various differences in the operational conditions. The FI, however, is a set device, no external influences can be done to manipulate the system but with the use of the ECU. The problem with the FI however is that it's fairly expensive to replace (parts of the FI cannot be replaced) the whole system. Where the FI takes claim of the prize though, is that the system improves the overall working environment for the engine, resulting in the parts of the engine staying durable and the engine producing peak power and with good efficiency. Pollution is another area where the FI wins as the subsequent emissions from the engine contains only the limited/regulated amount of pollutants.

Go back to Motorcycle Knowledge Base