Kill switch how-to

[MechEngVT]

dcb;

In multi-port fuel injected engines there is not a substantial amount of fuel sitting in the manifold. Port fuel injectors spray into the intake port onto the closed intake valve. The only way for this fuel to get into the manifold would be as it evaporates and then exhaust reverts out the intake valve at initial intake valve opening it may push some fuel vapor up the intake runner, but then the piston will draw this vapor back down the runner into the cylinder as the cylinder fills.

When an engine shuts down it doesn't instantly stop. It spins down to a stop over time as engines have substantial rotational inertia. When I EOC my truck I have to key-off for almost 2 seconds (from 2000 rpm or below) because after just 1 second if I key back on the engine still has enough speed to restart itself. At just 1000 rpm an engine rotates more than 16 times in one second meaning that each cylinder goes through at least 8 intake cycles. If you kill your ignition but not your fuel injection you will be injecting enough fuel onto your intake valve to be sucked into the cylinder for about 8 combustion cycles per cylinder that will not be burned before the engine stops. This fuel will wash oil off the cylinder walls, dilute the oil, and some of it will go out the exhaust as unburned HC and/or will collect in the catalytic converter where it will oxidize and heat up your cat. The fuel does not just "sit" in your intake manifold because your engine still pumps air as it is spinning down to a stop. The spinning doesn't stop instantly, so if you kill just your spark the fueling continues as the engine spinning continues even though you don't feel the jerkiness of sputtering combustion.

You are correct that any fuel in the oil will light off as the oil temperature heats up. This also takes time at temperature and if someone is frequently EOCing and minimizing engine load rather than P&G the oil may not get very hot and may not stay hot long enough to light off frequent additions of fuel from a power-on shutdown. Bottom line: it's fine if you want to cut the ignition to shut off your engine, but for pete's sake cut the fueling as well!

[Raysp30]

Can't seem to find anything that would be the fuse I'm looking for. There is no fuel injector fuse or a PGMFI fuse. Anybody able to help locate on an 89 crx?

If not, anybody have other ideas for a good kill switch method? The only one I'm still able to find that I know I can do is the fuel pump, and I don't really want to cut that one.

[bbjsw10]

Originally Posted by Raysp30

Can't seem to find anything that would be the fuse I'm looking for. There is no fuel injector fuse or a PGMFI fuse. Anybody able to help locate on an 89 crx?

If not, anybody have other ideas for a good kill switch method? The only one I'm still able to find that I know I can do is the fuel pump, and I don't really want to cut that one.

Use the wires on 87a and 30 on your Injector resistor power feed. Will work the same way. I ended up changing mine to this after writing how-to. I believe the injector resistor on your car should be close to brake booster and look like this.

[Raysp30]

Originally Posted by bbjsw10

Use the wires on 87a and 30 on your Injector resistor power feed. Will work the same way. I ended up changing mine to this after writing how-to. I believe the injector resistor on your car should be close to brake booster and look like this.

I think I see what you mean. Just cut into the red wire (power feed) and plug those into the relay? Do I still need to use the inline fuse with this setup? Appreciate the help.

[bbjsw10]

Originally Posted by Raysp30

I think I see what you mean. Just cut into the red wire (power feed) and plug those into the relay? Do I still need to use the inline fuse with this setup? Appreciate the help.

I would atleast use some type of fuse. Better safe than sorry.

[Impulse]

You guys should use a spdt relay and a momentary switch to disable the ignition, fused off of the igntion at or near the ignition switch itself. Pin 86 to the momentary switch, then the switch to ground, cut the ignition wire open, pins 30 and 85 will go to the wire coming off your ignition tumbler itself, and pin 87a goes to the ignition wire going down towards the car. Doing it this way, the relay ign connections are already fused through the factory wiring, but you should put a fuse between the chassis ground the momentary switch. If the relay ever fails it will rest at normally closed, and you ignition will still be connected, plus there are not wires through the firewall. If you guys like I can give people tech support and wires colors for your vehicles because I have access to it since I am a 12 volt installer. Just shoot me a pm. Just my .02 cents.

[bbjsw10]

The way I have this drawn up on schematic it goes back to a normally closed position. I would not cut into wire by ignition switch shuts off more than you need to shut off. Like your ecm and odometer all in one shot, and the all important ABS system and airbags. This is why I would not cut ignition off at switch with relay. Plus need odometer to figure mileage. I have installed also since 1995 and was Install manager at local ABC warehouse for about a year.

Originally Posted by Impulse

Pin 86 to the momentary switch, then the switch to ground, cut the ignition wire open, pins 30 and 85 will go to the wire coming off your ignition tumbler itself, and pin 87 goes to the ignition wire going down towards the car.

FYI: the way you describe you have the relay connected on normal open contacts. 87a is normal closed.

[Raysp30]

I had a relay from Radioshack that had 4 pins on it, no 87a. I hooked it up by splicing into the red wire on my fuel injector resistor. Once all the wires were in place I tried starting the car and it wouldn't turn over.

I found a different relay that was supposed to have the 87a pin on it, but there was only a stub where the pin should have been, and the packaging on that relay had never been opened.

Is there a 2nd wire I need to splice into to make this work?

[Gregte]

Regarding the concerns of cutting the ignition and then having a few extra cycles of fuel injected, carbureted cars do it every time you turn off the key switch.

[bbjsw10]

Originally Posted by Raysp30

I had a relay from Radioshack that had 4 pins on it, no 87a. I hooked it up by splicing into the red wire on my fuel injector resistor. Once all the wires were in place I tried starting the car and it wouldn't turn over.

I found a different relay that was supposed to have the 87a pin on it, but there was only a stub where the pin should have been, and the packaging on that relay had never been opened.

Is there a 2nd wire I need to splice into to make this work?

Get a relay from autozone or advance auto and preferably a Bosch relay. It will have to have all 5 like listed on the parts needed list. That or find a 4 pin normally closed relay.