eBay Library (FAQ)

Library (FAQ)

How do I know if my injector is low impedance or high impedance? - Back To Top

You can measure the resistance across the two electrical terminals of the injector. If the resistance is between 1.5 and 4.0 Ohm you have low impedance injectors.  If the resistance is between 8 and 16 Ohm you have high impedance injectors.

Can I check whether my injectors are working myself? - Back To Top

Occasionally you may want to verify that your injector is working (that the electromagnet is opening the injector valve). This is typically easy to do since the injector makes an audible click when activated. Since the coil wires are designed to be operated with a specific amount of current and the resistance of the tightly wound coil will quickly generate enough heat to melt the wires, we do NOT recommend that you activate your injector with a 12V feed from your car battery. Instead it is best if you use a low current source, like a 9V battery, which will activate your injector, but without the risk of damage from prolonged heavy current.

If you hear the injector “click”, you know the valve is opening. Of course this does not mean that everything is perfect, since only a flow and pulse test will determine if the injectors are operating correctly, but you are at least able to tell that the injector valve is not stuck open or closed, which can help you eliminate at least some de-bugging issues. Another simple test you can do at home is to test the resistance across the electrical contacts of the injectors. It is extremely rare to have more than one injector fail, so what you are looking for is one injector that does not match the resistance of the others. If the resistance is much higher or lower than the other injectors, there is an issue with the coil of the injector in question, and it will need to be replaced.  Injectors that exhibit this failure will typically not pulse during testing, or if they do pulse they will not flow nearly any fuel.

What is base fuel pressure? - Back To Top

Base fuel pressure is typically referred to as the pressure to which the fuel pressure regulator will set the start and idle fuel pressure in a particular fuel system.

Base pressure is important to us in the fuel injector industry and to tuners, since it is one of the factors that we use to define flow rate of the injectors, which in turn is something the ECU has to know to correctly meter the fuel delivered to the motor.

Rising rate Fuel Pressure Regulators (FPR) and Base Pressure - Back To Top

While many cars may have rising rate fuel pressure regulators that increase the fuel pressure in the fuel rail when the manifold pressure rises due to boosted applications, the base pressure is always the pressure that the injector operates at, since the added pressure due to boost is on both sides (manifold and fuel rail) of the injector. These two “added” pressures therefore cancel each other out and the ECU can carry on assuming that the injector will continue to deliver the same amount of fuel as when it was at “base” pressure.

At what Pressure will my injector fail? - Back To Top

Maximum operating pressures of HP- injectors vary from set to set. Most of our current line of high impedance injectors will produce a repeatable pulse to at least 115psi (8 Bar), while the low impedance injectors will produce a repeatable pulse to at least 80psi (5.5 Bar)

When considering the maximum operating pressure of an injector it is always important to remember that the additional fuel pressure added to the fuel rail is offset or “cancelled out” by the boosted air pressure in the manifold or head. The maximum operating pressure for the injector will therefore always be the base pressure and not the maximum fuel pressure reading that you may see from your fuel pressure sensor during peak boosted conditions.

Example: You have an injector that has a maximum recommended operating pressure of 100psi (6.9Bar). You are running 65psi (4.5 Bar) base fuel pressure and 30psi peak boost. Your fuel peak pressure is 95psi. Therefore you are operating within the limits of the injector (which is the pressure at which your pumps will have to deliver fuel.

Pump delivery pressure and the injector? - Back To Top

It is much more likely that the fuel pump(s) will fail to deliver the required fuel flow rate at peak boost (and therefore peak fuel pressure demanded by a rising rate FPR) than the injector failing because you have exceeded the maximum operating pressure of the injector. This is because the injector only operates at “Base Pressure”, while the pumps have to deliver at base plus boost. If you have ever looked at the delivery graph of a fuel pump, you will see how drastically the flow decreases as the required delivery pressure rises. It is not a linear relationship AT ALL so it is important to check that your pumps can deliver if you are planning to raise the base pressure (especially in boosted applications).

Because of this, it makes more sense to buy a larger injector and keep your base pressure lower, instead of turning your old 900cc/min (@43.5psi /3 Bar) injectors into 1100cc/min injectors at 65psi (4.5 Bar). For example, let’s say you are running 30psi (2 Bar) boost, suddenly your pumps have to deliver 1100cc/min per injector at 95psi (6.5 Bar) which is likely more than your fuel pump can handle. In this situation you would have to consider adding more (or more powerful) pumps (and dealing with the associated issues of putting too much heat into your fuel at idle or low throttle conditions) when instead you could just upgrade to larger injectors.

Do all cars use the same base fuel pressure? - Back To Top

No. While some typical base pressures (43.5psi [3 bar] and 58psi [4 bar]) are by far the most common, the OE manufacturers can choose any pressure they found suitable during their design.

It is important that you know at which base fuel pressure your car will run, because that will determine what flow rate your ECU has to be told your injectors will provide. If you buy a 650cc injector from us that has been rated at 43.5psi (3Bar) and your fuel system runs at 58psi (4Bar), your ECU has to be told you have 750cc injectors, otherwise your car will run 15% rich (or not at all)!

We typically mention the OEM base fuel pressure and the flow rate of our injector at that new pressure in the description when it is not the same as the HP-Injectors standard 43.5psi (3 bar) pressure that we will have rated the injector at [screenshot example]. However, if you or your tuner have selected a custom pressure to run, you should always make sure you know or calculate, what your injector flow rate needs to be to safely run your motor.

At what pressure does HP-INJECTORS flow test/rate their injectors? - Back To Top

When injectors are flowed at HP-Injectors, whether for flow matching or for cleaning services, we use the widely accepted pressure of 3 bar (43.5psi). When all injectors are rated on the same basis, it is easy for injectors to be selected by flow size for particular applications.

If the fuel system that the injectors will be used in does not operate at 43.5 psi (3 bar), they may have to convert their data (you can use a flow calculator,  but at least knowing that a 900cc/min injector is larger than a 800cc/min because they were measured on the same basis is made easy.

For example, OEM c5 corvette uses a 58psi  base fuel pressure, so their injectors would flow about 15% less at 43.5 psi. Knowing this, make sure you convert all flow rates to 43.5 psi when selecting the proper injector upgrade from our website.

Will your injectors plug into my wiring harness? - Back To Top

If you select your injectors from our website according the make and model in which they will be installed, you will receive everything you need to install the injectors into that vehicle. While most of our injectors “drop” right into your car, sometimes a particular flow size of injector not to be available with the plug that matches your application. This becomes more common with larger injectors since they are usually only available with one type of plug.

Every model-specific set of injectors that leaves HP-Injectors either fits your OE harness or comes with plug and play harness adapters.   Pig tails also available upon request.


So what about “the need for competitors to pre seat their injectors to reduce distortion”

A fuel injector, like any other mechanical device, will undergo an initial “wear-in” or break-in period during which its characteristics will change. We account for this by running every injector through a break-in period of 1 hour at 200 Hz. (720,000 cycles) PRIOR TO testing and flow matching.

This is just one of many steps that we take to provide consistency for HP-INJECTORS customers.