Kill switch signal cutting options
 

I've been contemplating doing a kill switch for a while now. I'm just not sure the route I want to take with it. There are several members who have done kill switches and everyone seems to do it a different way! I'd like to take some time to explain the different ways, their pros and cons, and hash out what we think might be the best way.


Cut ignition signal
Cutting the ignition signal is fairly easy. Its a single wire job, but doesn't necessarily ensure that fuel injection stops as soon as you activate the switch. Also won't work for diesels.

Cut fuel injector signal(s)
Cutting the fuel injector signal is a bit more complicated on most vehicles. On throttle body injection this isn't a great option as you still have fuel in the intake manifold and the engine won't die immediately. On batch fire injection, you have two or more wires to cut into and stop signals. On sequential injection you have at least four wires to cut into and stop signals. However, this approach ensures no fuel is used immediately after the switch is activated.

Cut fuel pump power
This is IMO not an ideal way to kill an engine. You have to wait for the engine to die as the pressure is bled out of the fuel system by the injectors. It is, however, a simple one wire option.

Cut the crankshaft position signal
I think dcb recently posted about using this method. I'm not sure if it cuts fuel and ignition all at once? If so, this would be great one wire solution.



So, add your method and/or discuss existing options so we can get an idea of what is best.

Perfectly timed post for me. I plan to do this to my Geo this weekend. I picked up a Haynes manual (from public library) last night so that I could have access to the electrical diagrams. I have considered all of the above options but, like you, could use some wisdom from those that have experienced this before us.

Most modern fuel injection systems supply power full time to the injectors. The ECU will supply a ground when it wants the injector to open, and then disconnect the ground to close it. There is usually a single source for the power to the injectors, which then gets split into individual power leads for the injectors. Find that single source, and you can kill all of the injectors by interrupting one wire.

Some cars use resistors to drop the voltage going to the injectors; usually the single wire goes in to that box and is split in there.

That's where I'm planning to hook in my kill swtich on doing to my CRX.

-soD

As mentioned, the best place I've found is either the camshaft sensor (if equipped) or the crankshaft sensor. It is low current, doesn't require extra relays, and has the effect of disabling the injection and the spark. Basically this tells the computer that the engine has stopped and it responds by turning off the spark and the squirt.

http://ecomodder.com/forum/showthrea...tml#post102167

I've tried about every kill switch scheme imaginable and I like this solution best so far.

If you cut the crank postion sensor circuit, won't you throw a code putting the emission system in open loop operation on restart?

CJ

No codes, not in my case anyway. A stopped engine is a normal state of being for a car.

On the engines you've used the cam or crank position sensor cut, does the engine have both sensors? I assume the engine uses one as a check for the other in most cases?

My switch is inline with the coil pickup in the distributor. Is this what you're referring to as "camshaft sensor", dcb?

The engine occasionally stumbles when it's used. That could be dieseling from fuel still coming through the throttle body - I don't know. I've never tried any other method.

My repeated advice - regardless of method chosen - use a momentary switch, not an on/off one. (Safety implications. You would think after hundreds of uses that you'd always remember to turn it back on, wouldn't you? ;))

My saturn didn't have a real camshaft sensor, so I tried the crankshaft sensor and it worked without a hitch.


I tried the camshaft sensor on the metro after trying other schemes. It also worked flawlessly. It is also tbi, as well as using a distributor. Dunno if that matters.

This is empirical evidence. I do not know every nuance of every car, and for all I know some cars might complain if you interrupt the injector or ignition circuit for that matter. I know the saturn would throw a code if you left the FI fuse interrupted for too long, and that the metro would run on if you killed just the fuel.

Edit: yup metrompg, the two wires coming out of the distributor, just interrupt one of them with a nc momentary contact switch (micro). It kills ignition and fuel at the same time and does not throw any codes.

Anyone else on any other options?

With out the cut off circuit we turn the key from ON to ACC, and then back to ON when engine has completely stopped. Then it is in the ON position waiting for a bump start or key start. This is a completely normal situation for any car.

Does interrupting the ignition wire at the key switch accomplish this seeming normal way of doing this?

Doesn't this ignition wire at key switch control the fuel and spark at the same time?

I've heard concerns of fuel with no spark and spark with no fuel as potentially problematic with the spark ignition only, or the fuel injector kill only options. Are these concerns even valid? I guess in either case you get a few extra sparks or some fuel pumping, but only till the engine is dead...then all things are truly stopped? Sensors and computer codes seem to be the only potential victims here.

Maybe my naivete keeps me from understanding that your solutions are probably providing the same solution. Since mine is old enough not to know what a computer code is I probably have less to worry about?

keying off also messes up the gauges in the saturn, the speedo takes several seconds to "come back online". The metro starts beeping at you. The mpguino also stops tracking speed/distance while the key is off and I'm sure a scangauge wouldn't be real happy either.

Got it. Thanks for the clarification. The dilemma makes sense now also.

I second MetroMPG's and dcb's approach, interrupting the signal on the wire coming from the Hall sensor on the distributor. In my car it's a yellow-and-green wire. Been using it for about 2 years without any problems. (At first I was afraid I might be damaging the catalytic converter, but the car just passed the emissions inspection with flying colors.) Should work on any engine, it will cut both fuel and spark. I bumpstart whenever possible but I also installed a start button, tapping a relay into the wire going from the key's starter switch.

Other options: My car doesn't have an injector fuse. Cutting the fuel pump would give a delayed response and I suspect the ECU may try to compensate for waning fuel before it dies.

I installed mine last weekend.
I followed this advice and it worked perfectly! Thanks!
I went with the black/white wire off the distributor on the Metro. According to the schematic they both should work as stated but black/white seemed a better choice.
I did use a small normally closed momentary which I mounted like a trigger on my shift knob. I was a bit concerned about the long term reliability of this momentary switch so I also added a bypass or override toggle switch in parallel before the momentary. This way if the momentary ever fails open (no start) I can flip the toggle it closes the circuit and things are running again.

Looking forward to effortless EOC. Now my blinkers still work in EOC, no beeps, and once I get my MPGuino finished it will also stay on. :)

Just an FYI, the guino will always stay on since it is wired to 12v constant. The problem is that when you key off, the sensors don't have any power going to them so the guino reads no signals from them. Glad it worked out for you! My turn next I guess. :)

For anyone who finds this thread, I'll add that there is a thread dedicated to Killing a diesel.

In my case (HDi commonrail turbodiesel) I can unplug the crankshaft sensor with no change in engine functioning. Unplugging the camshaft sensor doesn't stop the engine, only keeps it from starting if already stopped. No codes. Haven't tried pulling both sensors at the same time.

I know this is an old thread but thought this would be as good a place as any to ask. I bought a 94 metro xfi last month. Would it be better to use the red wire which is the ignition reference high or the white wire which is ignition reference low, or does it matter? My service manual says that at the ecm the red wire = light green pin b1 and the white wire = purple pin b9. Has anyone had problems using the wires under the dash as opposed to near the distributor? I only ask because for some reason many seem to have problems tapping into the fuel injector wire near the ecm when installing their mpguino ( which I received about 2 weeks ago but have yet to find the time to install.)

This is why I love owning pre-computer cars.
I did exactly what doviatt suggested, and it works great. Simple, reliable, effective.

On to the present:
On a car with DFCO, would there be a way to tap into that system, and activate in manually? Since it is built in, seems that might be the way to stop fuel to the engine which the computer and sensors and everything would object to the least

kill switch idea
 

I have been following this forum for some time. I have two 1994 metro's one auto and one manual. I have in my manual metro a brand new motor with 1 mm oversized pistons the compression raised to 11 to 1 ratio. stainless valves bronze guides 3 way cut on the valves and the motor was balanced. all marks on everything is to factory specs. I also did the grinding on the head i think it was call sign grooves? so i know have 1000 miles on it and it gets exactly the same gas mileage as when it had 176k on it. about 43 mpg

i'm documneting every thing in a note book as i drive to keep some records.

So now it begins trying to find the tweaks. my first tweaks i thought would be a kill switch and manual throttle handle.

My idea on the kill switch is to kill the cam sensor or distributor and use the clutch saftey start switch to do it. You dont need to cram the clutch pedal to the floor to shift so i thought why not disconnect the switch and have it interupt the cam sensor since you need to clutch the engine and kill the switch at the same time to be the most effective.

has it been tried yet?