One look at the fuel injectors on your car, and you'll wonder how they work at all, not to mention for tens of thousands of miles. Fuel injectors allow us to get gas mileage at the same time we develop additional horsepower and cleaner emissions.

The only thing your fuel injectors require in return is a steady supply of clean gasoline. That's why the fuel filter is so important to your fuel injectors--even a tiny piece of dirt or crud can foul up the mechanism inside your fuel injectors, so replacing your fuel filter regularly is essential. When your car left the factory, it may have been equipped with fuel injectors that leaned more towards the economy side of the equation than the performance side. With aftermarket fuel injectors, you can swing that equation over to the power side.

How does a fuel injector work?
A fuel injector is nothing more than a high-speed valve for gasoline. An engine computer or controller is used to control the fuel injector. Contrary to popular belief, this is not done by sending power to the injector. Fuel injectors are normally fed power whenever the ignition key is on. The computer controls the negative, or ground side, of the circuit. When the computer provides the injector with a ground, the circuit is completed and current is allowed to flow through the injector. This energizes an electromagnetic coil inside the injector, which pulls a sealing mechanism (pintle, ball, or disc) away from its seat. This makes it possible for fuel to flow through the injector and into the engine. When the computer removes the electrical ground to the injector, the electromagnetic coil becomes demagnetized and a spring forces the pintle, ball, or disc shut to cut off fuel flow. Even at an engine speed of just 1000 RPM , this is done hundreds of times per minute.

What do the terms “static” and “duty cycle” mean?
An injector in an engine turns on and off very quickly to control the amount of fuel delivered. The amount of time an injector is turned on and delivering fuel is known as the duty cycle. This is measured as a percent, so 50% duty cycle indicates that the injector is held open and held closed for an equal amount of time. When the engine needs more fuel, the time that the injector stays on (its duty cycle) increases so that more fuel can flow into the engine. If an injector stays on all the time, it is said to be static (wide open, or 100% duty cycle). Injectors should not go static in a running engine. If an injector is static in a running engine (open 100% of the time), that injector is no longer able to control fuel delivery. This could be an indication that the injector is too small for the needs of the engine. Injector duty cycle should usually not exceed 80% in a running engine at any time.

What is impedance?
Impedance is the electrical resistance of the electromagnetic coil inside the injector. This is measured in ohms and can be determined with an ohmmeter. Injectors are classified as either high-impedance (also known as “saturated”) or low-impedance (known as “peak and hold”). High-impedance injectors usually range from 11 to 16 ohms of impedance, while low-impedance injectors usually range from 0.7 to 5 ohms of impedance (these impedance numbers are based on what is currently available in the consumer market and are subject to change). Most OEM engine computers are designed to control high-impedance fuel injectors. Low-impedance injectors are generally preferred for racing or ultra-high performance use because they respond more quickly, but aftermarket engine controllers are usually required to control them.

What is an injector’s static flow rate?
Manufacturers rate fuel injectors by the maximum amount of fuel that they can flow in a given amount of time. This measurement is taken with the injector on 100% of the time (100% duty cycle, or wide open) and with the fuel at a given pressure (usually 43.5 psi). For example, a 19 pound per hour (Lb/Hr.) injector flow 19 pounds of fuel in one hour at 100% duty cycle and 43.5 psi of fuel pressure. Injectors in imported vehicles are often rated in cubic centimeters per minute (cc/min) instead of pounds per hour. This is also done at 100% duty cycle.

If injectors should not exceed 80% duty cycle under operating conditions, why do manufacturers rate them at 100% duty cycle?A test at 100% duty cycle is used to determine the maximum amount of fuel that will flow through an injector in a given time. This test is useful for determining whether an injector’s internal fuel passages were machined properly, but it does not check an injector’s ability to cycle on or off. It is usually not recommended to run an injector at more than 80% duty cycle under actual driving conditions. This 80% duty cycle operating limit is taken into account to make sure the injector will be large enough to feed the engine under actual operating conditions and will not starve the engine for fuel.

Signs And Symptoms

Here are some of the signs your car may show indicating that your injectors need servicing:

Poor Engine Performance
Poor Drivability
Poor Fuel Consumption
Cutting Out, Stalling
Rough Idling
Hard Starting
Loss Of Power
Flat Spots, Hesitation
Increase in Exhaust Emissions
Possible Catalytic Converter Damage
Lacking Performance

Reasons Your Injectors Become Dirty

Contaminates in the fuel tank and fuel lines cause a blockage in the micro filter
Fuel rail o-rings and manifold seals become hard and brittle and they deteriorate causing vacuum and fuel leaks
Petrol contains certain levels of wax type substances. These substances bake on the injector nozzle over time and this is the major cause of injector clogging
Injector tips can exceed 100c degree temperatures. When the engine is turned off, injectors absorb the heat of the engine (heat soak), with only 0.006" opening of the needle nozzle off the seat, deposits are easily baked into the seat, restricting clear flow of a mist of atomised fuel into the inlet port
The formation of deposits is related to the injector environment:
- The tip temperature in the engine design
- Frequency of warming up and switching off or 'stop start' driving
- L.P.G. used as the primary fuel (without the cooling effect of petrol flowing through often enough)

We can supply a diagnostic tool that enables you to test individual fuel injectors in the car. This will take the guesswork out of diagnosing faulty fuel injectors and save you time because you will only need to remove the fuel injectors if you know they are faulty.
With the help of a fuel pressure gauge and voltmeter it tests two things: