MGV101 Posted September 7, 2018 Report Share Posted September 7, 2018 I am rewiring my engine and building a custom loom for my MR2 with a Gen 3 3S-GTE engine and will be running it on a G4+ Fury. While studying the existing wiring, I noted the system uses a circuit opening relay for the fuel pump where there is a second coil to switch on power to the fuel pump while the engine is cranking. As I am deleting/replacing the whole fuse box along with the relay, will it work if I just use an ordinary relay for the fuel pump? The relay will be powered by an key-on power source with the coil grounded to the ECU fuel pump output. Will the G4+ switch on the relay during cranking to provide power to the fuel pump? Thank you! Quote Link to comment Share on other sites More sharing options...
cj Posted September 8, 2018 Report Share Posted September 8, 2018 This guy has a good explanation of what toyota calls a circuit opening relay https://bluetwentyeight.wordpress.com/2017/04/24/circuit-opening-relays-on-toyotas/ Its just a normal relay that can be triggered by 2 different triggers. The wiring diagram for both 5s and 3s sw20's still shows it wired i as a normal "apply Ground from ECU to close the circuit" setup. The link ecu's can control the fuel pump just fine with a normal single relay. I'm guessing the old toyota ecu's werent able to handle "power on only when cranking or running or for a couple seconds to prime at key on" so they used this dual trigger relay setup - factory it has 1 trigger from the clutch kill switch or park/neutral switch, and the second trigger is that FC wire from the ECU, so either of these will make the pump run. Quote Link to comment Share on other sites More sharing options...
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