The Purpose and Definition of Fuel Injector Pulse Width

engine top view
Fuel injection is important for the function of your vehicle. pictafolio / Getty Images

All modern automotive engines use fuel injectors to deliver fuel to the combustion chamber. Varying load, speed, and temperature conditions require adjustability of fuel delivery, and that is accomplished through changes to injector pulse width.

It is simply the amount of time, measured in milliseconds (ms), a fuel injector stays open (delivers fuel) during a cylinder intake cycle. 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, the onboard computer delivers more fuel by increasing the pulse width of the fuel injectors.

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 it up in a reference table wherein the relation between engine speed and load are explained. Once you determine the base width, you then determine which factors will affect your engine performance like oxygen levels and coolant temperatures and plug it into the equation "pulse width = (Base pulse)(Factor A)(Factor B)." 

However, it is important to know that your engine's pulse width is actually determined by as many as 100 or more factors such as these, wherein 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 for you, engines have determined this formula for years and have since perfected the process. Some cars now even have electronic monitors that can read out exact measurements of all factors that go into determining pulse width and hackers can even 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 fuel injection rate can affect your engine's performance, mainly because it is specifically designed to run with a certain ratio according to a multitude of factors. You can typically observe problems with the fuel injector in a variety of ways.

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

If your check engine light comes on, you should see your local mechanic or check the engine yourself by checking 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 your local mechanic for a full diagnosis and the most professional solution to your engine troubles.