3.4 Swaps The 3.4 V6 Toyota engine

Circuit Opening Relay and Fuel Pump

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Old Dec 7, 2019 | 12:08 PM
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From: exo-reality -wave if you see me; Front Range, CO
Circuit Opening Relay and Fuel Pump

Hi boys and girls.
I'm hoping this is the best place to post this Q.

I'm working on the 3.4 from a 99 (manual) into a 95.
Reading everyone's sticky's I'd probably be fine plunging on if no one answers, but I know some smart folks lurk here frequently. Better to speak and confirm being a dumbut than to break stuff later, and folks know anyway. AmIright?

Background.
It seems that the 95 connecting the Start on key energizes Starter Relay, energizing the COR relay, which provides complete circuit for the (separate power circuit) Fuel Pump, which power is fed via the EFI relay. AND the fuel pump is on anytime the key is "ON". (?) This seems like everyone uses this method in conversion, and works fine on 3.4L. Altho to be honest, I can't see why if the Start terminals energize fuel pump thusly, it would stay on after Start is released. So I've probly got that wrong, too.

EDIT: says right there in Service Hints: EFI and COR relays both closed pins 5-3 with Key ON. (CORelay on with key ON OR starter running.

The 99, with KEY ON, it energizes IGSW signal to E14-2 (ECM). So when cranking V is also applied to E14-7 (totally separate circuit).
Does KEY ON also then arm the EFI relay, thus providing V to +B and COR? It looks like MREL (E14-8) provides signal to energize EFI relay, which closes contacts (pin 5 on EFI relay being always hot, and closing that relay provides power for the COR, and fuel pump when the COR is energized by FC (pin E14-3)? Whatever FC means.

I guess my question is "Was that a safety thing or sumpin' for the 99?" As maybe the fuel pump does not run unless the coil side of COR is grounded by the ECM? So the EFI relay wont engergize and power the COR unless "all is good" somehow, and the ECM is ready? Lots of logic-magic in the ECM? It seems there's a Chicken V Egg thing going on here. Probably doesn't matter in the real world, but my luck it will bite my B-hind. Pretty much one reason I've opted to figure out the wiring vs paying someone else to deal with my problems.

Thanks in advance.

Last edited by coopster; Dec 7, 2019 at 09:09 PM. Reason: clarify when EFI and COR relays are ON
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