Megasquirt MS3 PNP Installation

The Megasquirt MS3 PNP (PLUG AND PLAY) model is an engine management unit designed to work with the vehicle's original installation and also maintain many of the MS3 features that will allow you to add anti-lag, traction control, turbo pressure control by speed or gears, launch control, etc...

Each PLUG AND PLAY model comes with everything necessary for the engine operation specified, and in models where possible, improvements such as sequential injection or sequential ignition have been added. You will find the specifications in the datasheet of each unit.

The vehicle's engine wiring connector is installed on one side of the unit, and on the other side, there are several connectors used for PC connection, CAN Bus connection, connectors for additional inputs and outputs, and a memory card slot.  

1 General Diagram

This manual explains the installation of additional inputs and outputs for all PLUG AND PLAY units. Depending on the model, some inputs or outputs may not be available, and in point 4 of this manual, you will find a summary where you can check your unit.

The general distribution of the additional inputs and outputs is shown in the following image:

Note: There are 4 ground pins (GND); these pins do not need to be connected to ground, they have been included as a safety measure in case any installation has issues.

2-User Programmable Outputs.

In addition to the outputs necessary for the PLUG AND PLAY operation of the unit, there are several additional outputs. These outputs are independent of the vehicle's original installation and are available unless otherwise explained in point 4. When a vehicle requires turbo pressure control (N75), variable distribution, or any other feature, it will be available in the vehicle's engine wiring connector in the same way as the original unit, so no installation is required, and it will also have the outputs explained below.

Some of these outputs have the name of the function for which they were initially created, but they can be used for their function or for the user to implement their own strategies. This could be as simple as turning on a LED or activating a relay to controlling a solenoid or valve in a closed loop, the options are:

• Programmable outputs (something happens when a setpoint is reached).
• 2D Maps.
• 3D Maps.
• 3D Maps in closed loop.

Some examples of how to connect warning lights, valves, solenoids, or relays are shown below:

Below is a list of the current outputs, the main function for which they are intended, their operation, and the maximum current allowed in each of them.

*Except as noted, consult point 4.

ATTENTION: The outputs not listed in the table above are installed in the original engine wiring connector and reserved for functions required by the original installation, so they cannot be used in any case as user-programmable outputs.   

3-Inputs.

In addition to the inputs necessary for the PLUG AND PLAY operation of the unit, there are additional user-configurable inputs for functions such as Launch control, Cut-Off, Cut-Shift, vehicle speed input (if possible in the original installation, speed will be taken from the PLUG AND PLAY connector), etc...

These inputs can be used for their intended function, or if not needed, for others that may be required. The following table shows these inputs, their function, the type of input, and the voltage they accept. Below the table, you will find a brief explanation of how to use them. Some of these inputs can be used as outputs, but they do not have a Mosfet or transistor installed, so their current is very low. We do not recommend using them as outputs unless you understand what you are doing, as this could cause irreparable damage to the processor.

*Except for exceptions, see point 4.

ATTENTION: The entries not appearing in the table above are installed in the original motor wiring connector and reserved for functions that the original installation may require, so they cannot be used by the user in any case. 

3.1-ADC (Analog to Digital Converter).

The inputs JS4, JS5, SPARE ADC, EGO 2, and EXT MAP are of the ADC type, converting an analog signal into a digital signal, but they can also be used as switching ground switches. These inputs only accept 5V signals. Below are some examples:

• Sensors: Allows converting the voltage from a sensor into a measurement, such as temperature, pressure, distance, etc. Most sensors will need a resistor connected to 5V.
• Potentiometers: Allow selecting a percentage of mixes between different maps. For example, between two turbo pressure maps, between two ignition maps, between two fuel maps, etc. They also allow controlling the sensitivity of a map, such as a very smooth or almost nonexistent traction control to a very aggressive traction control.
• Switch: Allows turning on or off a feature. For example, Launch control, traction control, dual map, etc...
• Accelerometers: Indicate vehicle acceleration on up to 3 axes.

Connecting sensors, potentiometers, switches, or buttons is done as shown below:

3.2-Ground Switching Inputs.

The inputs LAUNCH IN, DATALOG IN, TABLE SWITCH IN, PE1, and JS7 are ground switching inputs, and they have an internal Pull-Up to +12V. These inputs can be used in the following ways:

• Switches: Allows turning on or off a feature. For example, Launch control, traction control, dual map, etc.... Installation is identical to the one shown in the previous image.
• Pulse detection: For example, from external modules like a knock sensor, speed sensors, or wheel sensors (explained in point 6.5), etc...

3.3-Dedicated Inputs.

Some inputs have been created for a specific feature, but if not needed, they can be used for other functions.

• FLEX: Designed for a Flex Fuel sensor, this sensor measures the percentage of ethanol in the fuel. Normally this fuel is mixed with gasoline in a percentage, for example, E85 means 85% ethanol and 15% gasoline, but these amounts can vary from one gas station to another or if the previous tank was 100% gasoline and wasn't completely emptied. The sensor will measure and send a signal to the ECU with the exact proportion of ethanol and gasoline. Based on this proportion, the fuel, ignition, and turbo pressure maps can be adjusted. If this feature is not needed, the input can be used for ground switching or pulse input in other functions. Accepts 5V signals, never 12V.
• NITROUS IN: Designed to receive signals from a Nitrous system. These systems usually send a +12V signal when active to change maps in the ECU. Therefore, this pin expects +12V for activation and not ground switching. If this feature is not required, the input can be used as a pulse or +12V switching input, remember that +12V is needed for activation and not ground switching. It only accepts +12V signals.
• PT4: Direct input to the processor, designed for crankshaft signals with optical or hall sensors at high frequencies, it will not work with inductive sensors. It can be used for pulse input or ground switching. Only accepts 5V signals.

3.4-IN-OUT Pins.

The PT4 and JS11 pins can be used as ground switching inputs or low current outputs. These pins are directly connected to the processor, and it is not recommended to use them as outputs if you do not understand what they do.

3.5-Connecting vehicle speed or ABS sensors to indicate speed, gear indication, or traction control.

There are several types of sensors in vehicle ABS and speed systems, Hall sensors, inductive sensors, and magnetoresistive sensors. For traction control, it is necessary to have at least one signal from a front wheel and a rear wheel, ideally from all four wheels. To know the vehicle speed, it will be enough with the signal from one wheel or a speed sensor installed in the gearbox or differential, many vehicles already have this sensor. The number of teeth on the installed phonic wheels, differential ratio, gear ratios, and wheel diameter must be correctly configured for proper functioning.

Identifying the type of sensor used by the vehicle and how to connect it to the unit requires testing and investigation. The way to ensure the sensor is working is by checking how it is connected originally before disassembling, measuring voltages on the terminals, and checking the signal they send to the unit using an oscilloscope. A brief explanation of the sensor types and their identification is as follows:

• Hall sensors usually have 3 wires, power, ground, and signal, although in ABS systems many only have 2 wires, power, and signal. The phonic wheel can be a disc with holes or toothed. These sensors send a square wave signal and can be connected directly to the unit without needing any additional circuit.
• Inductive sensors have 2 wires and may have an anti-parasitic mesh. They usually use toothed wheels, but there are also some with discs and holes, in which case they often have a metal base behind the holes making it toothed. The signal from these sensors is alternating, and their voltage varies with the wheel speed, so they need a circuit to adapt this signal to a square wave that the unit can accept. This circuit is installed inside the unit, its purchase and installation are optional, and if needed, it must be selected during purchase.
• Magnetoresistive sensors can be identified by the type of phonic wheel used, which doesn't have holes or teeth, using a smooth disc or wheel, making it the easiest sensor to identify. They need an external circuit to function, which is currently unavailable.

The connection for a speed signal from the vehicle can be done in the following ways:

Hall sensors are mostly ground switching; their connection is identical to the one shown for crankshaft or camshaft Hall sensors but connecting the signal to the pin indicated below. Depending on the voltage applied to the signal, it can be connected as follows:

• +12V signal: the inputs, NITROUS IN, JS7, PE1, LAUNCH IN, DATALOG IN, TABLE SWITCH IN, have an internal Pull-Up to +12V, so no external resistor is needed. Keep in mind that these inputs are for low frequency, wheels with few teeth.
• +5V signal: the inputs PT4, JS11, FLEX are perfect for +5V signals with high frequency. A 1K Pull-Up resistor will need to be installed.

The following image is an example of the connection for 4 sensors from the ABS hall or inductive system. It requires an internal circuit we are working on, and we expect to have it available soon:

4-Available Inputs and Outputs, depending on the model:

The table below indicates the type of input, pin, and maximum input voltage for the input signals for the current Megasquirt MS3 PNP version. The maximum voltage for all signals is +16V, and the unit will protect itself by turning off the input, but it is better to install it correctly from the beginning.

The table shows the available input and output types for different configurations of the Megasquirt MS3 PNP ECU.