What’s The Difference Between High Impedance and Low Impedance Fuel Injectors?

If you're shopping for replacement fuel injectors, you've probably noticed that there are two types of impedance ratings - high-impedance and low-impedance. The fuel injector's impedance relates to the electric current used - i.e. the amperage and resistance used by the injector to deliver fuel to the combustion chambers.

Most OEM engines use high-impedance fuel injectors, but it's important to know the difference. Using the wrong kind of fuel injectors will lead to performance issues and could cause problems with your vehicle's ECU and other engine management electronics.

With that in mind, let's look at the differences in fuel injector impedance and its application.

High Impedance Fuel Injectors

High-impedance injectors use a low-amp current with an impedance of 10.9 to 16.8 ohms. The low-amp current keeps the injector cooler making it more reliable, improving the longevity of the injector and your engine's electronics. Most cars use high-impedance injectors for these reasons and they are the most common type of injector on cars made today.

Low Impedance Fuel Injectors

Also called peak-and-hold injectors, low-impedance injectors receive a more powerful electrical signal with a lower impedance of 2.3 to 4.5 ohms. This type of injector runs hotter but is more responsive, opening and closing quicker than a high-impedance fuel injector. Low-impedance fuel injectors were more common in the 1980s and 1990s. They were used predominantly on turbocharged cars of those eras, but are still used today in some aftermarket and race engines.

Which Is Better?

The answer to which type of fuel injector is better depends on the application. Just about every production vehicle made in the past 25 years uses high-impedance fuel injectors as OEM equipment because of their reliability and longevity. Any benefit to switching to low-impedance fuel injectors would be extremely minimal and not worth the cost or effort.

Where low-impedance fuel injectors have an advantage is in race engines or any application where higher fuel demands are required for performance. However, there is more to it than just adding low-impedance fuel injectors. You also have to make sure your ECU and ignition system can handle the electrical load and additional heat generated by that load. If not, you will eventually fry your electronics due to the additional current and heat buildup.