Fuel Injection


How do fuel injection systems know how much gas to squirt??? Somewhere along the line, somebody realized that you could measure how much gas your engine needed by how much air it was sucking in. Once your engine starts, the measuring of air begins. Early fuel injection systems used a vane system, which was basically a flap inside a tube, to measure how much air was being sucked. Later systems used a “hot wire” to figure it out. When you turn your engine on, the wire becomes red hot. As air is sucked past this wire, it gets a little cooler. The car’s brain measures exactly how much cooler it is getting and uses this number to figure out how much air it’s sucking. Then it squirts the correct amount of fuel into the engine.

Fuel injection is a single fuel line that connects to a fuel rail on top of the engine. The injectors take gas from the central fuel rail and squirt in into the engine when told to do so.

NOTE: there are lots and lots of variations to fuel injection systems. We’ve got electric fuel injection, mechanical fuel injection, systems with one oxygen sensor, and systems with four oxygen sensors. But the basics remain the same.

In the beginning, gas powered vehicles used a carburetor to get gas into the engine. This worked well, but when fuel injection came along, things changed quickly. Fuel injection, especially electronic fuel injection produces fewer emissions and greatly increases gas mileage.

The carburetor was an ingenious invention in itself. Your car’s engine has 4 cycles or more, and one of them is a “suck” cycle. Put simply, the engine sucks (creates extreme vacuum inside the cylinder) and when it does, the engine. The carburetor was there to let the right amount of gas and air gets sucked into the engine. While great, this system lacked the precision of a pressurized injection system.

Your engine still sucks, but instead of relying on the suck, fuel injection shoots exactly the right amount of fuel into the chamber. Fuel injection systems have gone through a few evolutions, adding electronics was a big step, but the idea has remained the same. An electrically active valve (the injector) spraying a metered amount of fuel into your engine.

Multi-port injection is still widely in use today. So far it’s the most efficient method of metering gas into the engine. Multi-port fuel injection, also know a MFI, consists of an injector for each cylinder in the engine. This injector sprays fuel directly through the intake valve or valves into the combustion chamber. Each injector is activated separately by wire.


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