Using the Peak and Hold Injector Driver Board

The Peak and Hold Injector Driver Board drives up to eight peak and hold injectors. It can work with any MegaSquirt products, other standalone engine management, and OEM ECUs. The board takes an input siganl from an ECU intended to run saturated injectors, and uses its internal circuitry to regulate the current flowing through the injectors. When an injector opens, the current flowing through it will increase until it reaches the peak limit of 4 amps. At this point, the Peak and Hold Injector Driver Board will go into hold mode, limiting the current to 1 amp until the signal controlling the injector is turned off. If the battery voltage is too low to allow 4A to be reached, the full battery voltage will be applied for a period of about 3.9ms after which the driver will go to the hold phase and provide 1A.

Using the Peak and Hold Injector Driver Board provides faster and more consistent injector opening times than driving low impedance injectors through resistors. It also provides better cold start performance than resistors since the injectors get full battery voltage to open them; when using injector resistors, the injectors may not even open if the battery voltage drops too far.


The Peak and Hold Injector Driver Board attaches to a flat surface with the mounting tabs on its lid. The case is not waterproof, and it will get hot during operation, so take these into account when looking for a location to mount it. We don’t recommend installing it under the hood.

The five black ground wires should be crimped or soldered to a single lug and grounded to the engine block. If grounding them to the engine block is not an option, the second best choice is the battery negative terminal. The red 12 volt power wire needs to be connected to a source that gets 12 volt power with the ignition key in both the Start and Run positions. A 3 amp fuse will be sufficient.

There are two bundles of white wires that connect to the Peak and Hold Injector Driver Board. The ones in the bundle labeled INPUTS FROM ECU connect to the injector driver outputs on the ECU. The wires in the bundle labeled OUTPUTS TO INJECTORS connect to the injectors. Both sets of wires have identical stripes on the input and output side, so the wire in the INPUTS bundle will control the identical wire in the OUTPUTS bundle.

ECU Settings

If you have an ECU that has an option of using PWM current limiting (such as the main board injector drivers on a MegaSquirt V2.2, V3.0, or V3.57 board), turn this option off. Other than that, no special tuning settings are required. The peak and hold circuitry works automatically and does not require tuning. You may need to adjust the injector dead time if you were previously running low impedance injectors through resistors, as the peak and hold method of driving injectors results in a faster opening time.

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