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Media post: How Fuel Injection Systems Work


In the old days, car engines used devices called carburetors to vaporize engine fuel. Carburetors did a great job and were simple to troubleshoot and repair. Carburetors were the only game in town until the 1950s when automotive engineers started experimenting with other methods to deliver fuel to combustion cylinders. There was a desire for a more accurate fuel delivery system because this would lead to higher gas mileage and lower emissions.

In the early 1950s, fuel injection systems were developed. These systems allowed precise amounts of fuel to be metered directly into the cylinders. One of the first to be installed on a car was a mechanical system developed by General Motors and offered in 1956. These mechanical fuel injection systems soon gave way to electronic systems which are simpler and more accurate. We spoke to the service techs at West Valley Chrysler of Canoga Park, CA, a full service Chrysler, Dodge, Jeep, Ram dealer, and got a complete lesson in how fuel injection technology works.

How they work

A modern fuel injection system works like this: When you turn the key on in your car, the engine control computer (ECU) sends a signal to the fuel pump relay which powers on the fuel pump for a few seconds. Sometimes you can hear the fuel pump humming away when you turn the key. Once the fuel pump is on, it draws gas from the gas tank and sends it to the fuel filter, then to the fuel pressure regulator and then to the fuel rail that straddles the engine block. The gasoline at this point is under some 35-50 PSI pressure and sits waiting for the fuel injectors to open up.

The fuel injectors are controlled by the ECU which sends an electronic signal to each injector when fuel is needed. The precise amount of fuel injected is controlled by the ECU and will vary depending on the conditions at the time. Different amounts of fuel will be squirted into the engine depending on whether you either idling, cruising, or accelerating.

Sensors everywhere

Today’s electronic fuel injection systems utilize lots of sensors that feed information back to the ECU. This allows the ECU to know precisely where the engine is in its combustion cycle. For example, most systems have two sensors connected to the ECU. The first is the crankshaft position sensor. The second is the camshaft position sensor which sends a signal letting the computer know what position the intake and exhaust valves are in.

The amount of fuel that is injected into the engine is controlled by the ECU also. The ECU controls this delivery by monitoring many other sensors. For example, the mass air flow sensor (MAF) tells the computer how much air is being pulled into the engine. The throttle position sensor lets the ECU know how much you are accelerating. The coolant temperature sensor lets the ECU know what the temperature of the engine is. The air temperature sensor lets the computer know the temperature of the air entering the engine. The oxygen sensor lets the computer know how much oxygen is leaving through the exhaust system.

Complex but not difficult to fix

You may be thinking that modern fuel injected engines must be a horror show to repair. Actually, they aren’t because of the electronic diagnostic systems they have today (OBD-II). These systems allow technicians to plug code readers into to identify problems. This has revolutionized the ways cars are repaired today.

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