Function of Fuel Injector Pulse Width

It determines the amount of fuel going to the combustion chamber

Fuel injector of an engine

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All modern gas-powered automotive engines use fuel injectors to deliver fuel to the combustion chamber. Varying loads, speeds, and temperature conditions require the fuel delivery to be adjustable, and that is accomplished through changes to injector pulse width.

Injector pulse width is the amount of time, measured in milliseconds (ms), that a fuel injector stays open (delivers fuel) during a cylinder intake cycle. The typical injector pulse width for an idling engine at normal operating temperature is between 2.5 and 3.5 ms. When an engine needs to make more power—to accelerate onto a highway, for example—the onboard computer increases the pulse width of the fuel injectors to deliver more fuel.

How Pulse Width Is Determined

In terms of engine mechanics, the determination of fuel injector pulse width is fairly simple. First, you determine the base pulse width by looking in a reference table where the relation between engine speed and load is explained. Once you determine the base width, you then determine which factors will affect your engine performance, such as oxygen levels and coolant temperatures, and plug them into the equation "pulse width = (Base pulse)(Factor A)(Factor B)." 

In reality, however, your engine's pulse width is determined by 100 or more factors such as these, and a reference table can be used to determine the corresponding metrics for this equation. For instance, a coolant temperature "Factor A" of 75 is valued at .9 in the above equation via its reference table.

Fortunately, manufacturers have been using this formula for years and have perfected the process. Some cars now have electronic monitors that can read out exact measurements of all factors that go into determining pulse width, and hackers can program them to boost engine performance by adjusting the equations. This is not recommended for novice mechanics or mechanics with little experience with engine control modules (ECM). 

What Can Go Wrong

Even the smallest amount of variation in the fuel injection rate can affect your engine's performance, mainly because it is designed to run with a certain ratio according to a multitude of factors. You can observe problems with the fuel injector in a variety of ways.

A fuel smell coming from the engine compartment, for example, might mean that the fuel injector is creating a pulse width that is too long. A misfiring of the engine or a decrease in power, acceleration, or speed might be symptoms of a failing fuel injector. In any case, your vehicle has a built-in safety message to prevent a related spontaneous breakdown: the "check engine" light. 

If your check engine light comes on, you should see a mechanic or check the engine yourself by looking up the OBD-II code that your vehicle's ECM outputs. If you see a code that references fuel injector failure, the only solution might be replacing your fuel injector. In any case, it is best to visit a mechanic for a full diagnosis and the most professional solution to your engine troubles.