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Old 07-15-2012, 08:12 PM   #1 (permalink)
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Question Kill switch electrical questions

Disclaimer: I am not an electrician! Which is why I'm having trouble figuring out just how to go about installing a fuel injector kill switch on a 7th gen Civic. First, the schematic:



Unlike the 5th and 6th gen cars, it seems my 2005 has two FI relays (each marked "main," confusingly)--Relay 2 grounds through the fuel pump, and Relay 1 through the ECM? So, do I have to cut both of them or just one? Would cutting the ground from Relay 2 cause fuel pump issues when trying to start the car again? Would cutting the ground on just one relay even shut down all the injectors in the first place?

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Old 07-15-2012, 08:37 PM   #2 (permalink)
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IMHO, don't cut power to the fuel pump. Cut power to the common hot wire to the fuel injectors.
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Old 07-15-2012, 08:42 PM   #3 (permalink)
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Quote:
Originally Posted by Vman455 View Post
Relay 2 grounds through the fuel pump, and Relay 1 through the ECM? control circuit of both are grounded/switched by the ecm So, do I have to cut both of them or just one? Would cutting the ground from Relay 2 cause fuel pump issues when trying to start the car again? just cutting power to the fuel pump wont immediately kill the engine, residual pressure in the fuel system will allow the engine to keep running for a short time, longer when you're just coasting Would cutting the ground on just one relay even shut down all the injectors in the first place?cutting power to relay 1 would shut down the injectors, along with several other things in, and beyond what is shown in the provided diagram
what i would want to do is find the yellow/blk wire just before it splits off to the 4 injectors and wire in a switch/relay at that point
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Old 07-15-2012, 09:30 PM   #4 (permalink)
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Quote:
Originally Posted by 2000mc View Post
what i would want to do is find the yellow/blk wire just before it splits off to the 4 injectors and wire in a switch/relay at that point
Ha--I was so focused on the relay ground, that didn't even cross my mind! Thanks!
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Old 07-15-2012, 10:15 PM   #5 (permalink)
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I found the yellow + black wire at a 9-pin connector near the driver's side hood hinge. I think maybe only 8 wires there, but it's a 3x3 layout. That connector might still be there on your Gen 7, mine is Gen 6.

Other people have tapped into the computer's connectors. I'm just not comfortable working on those connectors with dozens of tiny pins and wires. But I know it's been done successfully.
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Old 07-15-2012, 10:44 PM   #6 (permalink)
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Here's how I wired mine, thread. The principle's the same for your Honda, cutting your yellow/black wire.
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Old 07-16-2012, 09:39 AM   #7 (permalink)
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for the understanding of the wiring:

both relais are grounded through the ecu. the fuel pump gets power over relais 2. relais 2 is switched by relais 1 and ecu. don´t be confused, by the upside down relais 2.

so, if u have troubble to find the injector wires, u can also cut the wire from relais 1 (coil) to the ecu.
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Old 07-16-2012, 12:33 PM   #8 (permalink)
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I cut the ground for my PGM-FI relay and that also shuts down the fuel pump. I have been driving like this for almost a year, heavily using the switch. No fuel pump issues. Fuel pressure remains fine, because pressure just does not leak from the line in seconds (barring a leak). CAUTIONS: I am also not an electrician, and therefore want to warn you not to rely just on this FI wiring diagram when deciding where to cut a wire. Consult other wiring diagrams too. When I was installing my alt kill switch, the alt wiring diagram showed me what seemed a good place to cut, but it was not revealing that where I planned to cut would also disable an O2 sensor. Do this slowly, and do your mod reversibly first, so you can test effects of changes and avoid troubles. Lastly, the advantage of cutting the ground to the PGM-FI is that there will be no live power running through your switch. I get a nice clean cutoff too. I hope that info is helpful.
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Old 07-17-2012, 01:24 AM   #9 (permalink)
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Based on the above diagram with what is visible, I would cut the ecm wire or red/yel wire, this will have the least amount of current of any of the lines and will cut off the ecu along with the fuel pump/injectors/ign, ect. If I could see the rest of the wiring, that may change but I doubt it.

Cutting the FP only will allow fuel to trickle through the injectors under low manifold pressure. Some cars will even run without the FP being on if they are of the centrifugal type.
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Old 07-17-2012, 01:20 PM   #10 (permalink)
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Just look for the injector ground and cut that

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