How Do I Know if My Injector Is Low Impedance or High Impedance?

February 13, 2020 Published by Leave your thoughts

There are two main types of injectors: low impedance and high impedance. A low impedance injector will have a resistance of around 2.5 to 3 ohms, while a high impedance injector will fall somewhere around 12 ohms. Resistance can be measured with a multimeter across the injector’s electric terminals.

When it comes to how you can know whether your injector is low impedance or high impedance, this really depends on the kind of vehicle you have. Here’s some information to consider when attempting to classify your injector. Contact a trusted diesel engine repair shop in Corpus Christi, TX for more information.

Low impedance or high impedance?

The more modern the system, the more likely it is the injector is high impedance. Let’s look at Honda as an example. Its early models used primarily low impedance injectors with a resistor pack. However, between 1992 and 1996, the company began transitioning to high impedance injectors without a resistor pack.

The resistor pack is a crucial element for low impedance injectors. When a low impedance injector is installed without a resistor pack, certain elements of the system are much more likely to get burned out, as the current will not be controlled properly. This is why it’s so important to know if you’re dealing with a low impedance or high impedance injector; a high impedance injector will not require a resistor pack, but a low impedance injector will.

Pay attention to the bottom specification Tj of 150 degrees Celsius, which relates to the transistor pack’s maximum junction temperature. The junction temperature is the temperature of the transistor that is embedded inside the package. The greater the current, the greater the temperature, and the more likely the reliability will be affected. While temperature is a pretty straightforward measurement, reliability is not, and can take a bit of time to measure.

High impedance injectors, as mentioned above, are much more common in use today. The drive circuitry for high impedance injectors is quite simple and referred to as a saturated driver circuit.

With low impedance injectors, you’re more likely to find them in larger, higher performance injectors. The driver circuitry used with these injectors is referred to as a Peak – Hold type of circuit, and is much more complex (and therefore expensive) than the saturated driver circuits in high impedance injectors. In this kind of system, the driver circuit allows a high current to exist for a short time to turn on the injector quickly. That current then gets brought back down to a lesser value to keep the injector open during operation.

The lower coil resistance in a low impedance injector allows the internal spring pressure that holds the pintle closed to be increased so the injector can be shut off quickly. The result is faster opening and closing times, which makes for easier tuning of the injector, particularly if it’s large.

This is just a little bit of information to give you a sense of the differences between high and low impedance injectors. Contact Coastal Diesel Injection today for more info about diesel engine repair in Corpus Christi, TX.

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