Standard Port injection injectors are controlled by one of 2 possible control circuits known as Injector Drivers. One is called a Saturated driver and is HIGH impedance. The other is called Peak and Hold and is LOW impedance.
Saturated Injector Driver
An injector used in a saturated driver is typically* HIGH Imp (12-16 ohms) as this is required to operate at low current levels ( 0.8 – 1 amp) using a higher resistance to keep the circuitry cool so the components can ensure a long life. When using a Saturated driver, the low current creates a slow response time which limits the dynamic range of the injector. Ohm’s law (V=IR) shows the relationship between current level and injector resistance. V=Voltage, I=Current (amps) and R= Resistance (ohms). A high impedance injector (12.5 ohms) used in a 12 volt system would require an operating current of 0.96 amps.
I = 12 Volts/12.5 ohms = 0.96 amps
Peak & Hold Injector Drivers
Low resistance (Impedance) injectors are used in Peak and Hold driver systems. These low Imp injectors ( 2 – 4 ohms ) require more current to open ( 4 – 5 amps ). If this driver was required to operate at 4 to 5 amps continually, it would overheat. Therefore, the circuit has a built in switching mechanism which allows it to hold the injector open at a lower level once the injector is opened. This is where it gets the name Peak and Hold. It Peaks with a high opening current, but Holds it with a lower more reasonable current for the duration of the called for pulse width because the injector is already open. It doesn’t take much to KEEP the injector open.
Most Peak and Hold drivers drive 2 injectors each. This means drivers provides 2 amps per injector and holds with 0.5 amps. Peak and Hold systems are typically used in higher horsepower, small displacement engines. The reason being is it allows for a more dynamic operating range of the injectors allowing a quick response time of the injector which is a huge advantage over a saturated driver.
What is Compatible with What?
Saturated driver circuits should not use a low impedance injector. This is not recommended. The additional amperage required to open the injector can overheat and burn out the driver. In addition, the injector can become unstable causing many other drivability issues. If you must use a low imp injector in a saturated driver circuit, you can add resistors to the system. We have a calculator to help determine what ohms and watts to use to still be able to use a higher flowing Peak and Hold injector in your circuitry.
*It IS however possible to run a saturated (high imp) injector in a peak and hold driver circuit. The amperage required to open the injector is within the specs of a high imp injector.
If you were to look on an oscilloscope, the figure below would show the waveform of each type of circuitry.