The ECU controls the power to all the hardware via the power relay circuit. These relays also act as a safety cutout for the fuel pump in case of engine stalls. When you switch the ignition on, the ECU will switch the relay output on for 3 seconds. If the engine is not cranked in that time it will be shut off again. This is to prime the fuel rails. In case of an accident these relays will be shut down in one second after the engine has died. This will stop the fuel pump from pumping fuel in ruptured lines. Note: Do not connect control hardware like coils and pumps to other power sources other than the Orion relays, as they will feed back power after the ECU is switched off. They must be connected to the control relays.
Mechanical Relays
Always use at least 2 mechanical relays. For 3 or more coils you may add a relay in parallel with relay 2 to share the load. do not connect coils, injectors, or fuel pump with relay 1 if the positive drivers is used. this may cause interference with the drivers’ operations. On large systems like 8 coils or more, you may add a fourth relay to share the load. Use Relay 1 for clean power for the ECU and lambda sensor. Use Relay 2 for injectors and fuel pump. This will prevent uneven voltage drops on the line that will cause the injectors to open unevenly resulting in fuel mixtures variation. Use Relay 3 for coils which create high voltage inductive spikes. Always make sure there is a 6-amp diode on each relay specially if there are inductive loads on them like coils, injectors and fuel pump. The stripe must be on 87 and the other side on earth.
Pin 86 of the Relay 1 is tied to batter positive. Note that some of the older Mercury2 units had a built in freewheel diode which prevented the ECU from switching off when the key is switched off. In these cases, connect Pin 86 to ignition power that feed the ECU power on the P1. See the drawings for more instructions.
Note: There is a diode on Relay 1 pin 86 and 85 that will prevent spikes and relay buzz. Do not use this relay for other inductive loads.
Click on the links below to open the relevant drawings.
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