Kill switch how-to

[bbjsw10]

Originally Posted by Clev

Would the fuel system keep pumping in fuel if the car is moving in gear with the ignition killed?

You shouldn't kill the engine with it in gear. Is what I would think.

Originally Posted by MetroMPG

I should do a writeup of my ignition coil kill switch method. It would be interesting to compare the two methods to see if there's any difference in the way the car stops/restarts.

Do it!! People need choices. I did mine like that but didn't like the idea of pumping in fuel that didn't burn. But mine is TBI so it is a little different than some. Takes more time for fuel to reach cylinders than MPFI does.

[MetroMPG]

I doubt it, but I've never tried that.

[MetroMPG]

Originally Posted by bbjsw10

Do it!! People need choices. I did mine like that but didn't like the idea of pumping in fuel that didn't burn. But mine is TBI so it is a little different than some.

Mine's Throttle Body Injection also. I'll add it to the to-do list for when I get back.

[Clev]

Originally Posted by bbjsw10

You shouldn't kill the engine with it in gear. Is what I would think.

In my case, what I need is to be able to kill the fuel but still use engine braking (17+ mile downhill from my house.) I'll have to try out a fuel pump kill.

[MetroMPG]

Ah, now I see what you're asking.

Your car already has a feature called Deceleration Fuel Cut Off (DFCO). I'm not exactly sure what your specific RPM threshold is for this state to be active, but it's likely your fuel is already off under those conditions.

Build yourself an MPGuino, and you'll know for sure!

[Clev]

Originally Posted by MetroMPG

Ah, now I see what you're asking.

Your car already has a feature called Deceleration Fuel Cut Off (DFCO). I'm not exactly sure what your specific RPM threshold is for this state to be active, but it's likely your fuel is already off under those conditions.

Build yourself an MPGuino, and you'll know for sure!

Yeah, I'll have to do that. As my speed drops, I eventually start hearing a slight burble from the exhaust, indicating to me that at least a little fuel is getting in. My one key-off test indicated that I could get all the way down with the key off, except for about a 4 second light 5th-gear acceleration after a particularly sharp corner. Having the fuel cut off the whole way seems like the way to guarantee that I don't use a drop of fuel the whole way down.

Seems like an MPGuino should be my second mod (after a vacuum gauge, that is.)

[Funny]

I know I am quite late getting in on this thread, but I'm surprised that no one has suggested the best of both worlds... Cut off BOTH the Injectors AND the Ignition. It would be a less than complicated bit of wiring to have a couple relays work off one momentary switch. Just an observation, as I plan to make the above mod to the Rolling Lemon in the very near future.

Also, a question for all those that are far more informed than myself, If the injectors are shut off and the fuel pump is still running, won't that cause undue stress on the fuel pump? Or is there a return line on most fuel injection systems that prevents this? All comments are appreciated.

[dcb]

Originally Posted by Funny

I know I am quite late getting in on this thread, but I'm surprised that no one has suggested the best of both worlds... Cut off BOTH the Injectors AND the Ignition.

LOL, see post #2

Kill switch how-to


You have to be careful how you kill the ignition, camshaft sensor seems to work well on metros but the low tension coil lead doesn't seem a reliable place.

Oh, and MPGuino users might have to add a 10k pullup (to 12 volts) resistor if they add an injector kill switch, otherwise playing with the kill switch will look like some serious injector duty cycle.

[Funny]

Originally Posted by dcb

LOL, see post #2

My mistake, it has already been stated. However the solution (i.e. Schematic Diagram.) has yet to present itself.

Originally Posted by dcb

You have to be careful how you kill the ignition, camshaft sensor seems to work well on metros but the low tension coil lead doesn't seem a reliable place.

This is a very important point, my only question about the statement is most vehicles are equipped with a fail-safe just in case the engine stalls while the car is in motion? We are just inducing a stall situation, right? So what's the fuss about?

[dcb]

Update, sorry this didn't sink into my head till now, but on the metro at least (and probably many other cars) YOU ONLY NEED TO INTERRUPT THE CAMSHAFT SENSOR CIRCUIT. I just ran some real world tests to confirm this. This would be a good wiki thing.

Let me explain,

interrupting the camshaft sensor tells the computer that the engine is now doing 0 rpm. The computer responds by sending out an ignition signal appropriate for 0 rpm AND an injector signal appropriate for 0 rpm. In other words, it stops both the ignition and the injector.

I confirmed this by monitoring the mpguino instant injHIus while coasting in gear while pressing the camshaft circuit interrupt kill switch. when I hit the switch, the injHIus would go to 0 even though the engine was still turning over via engine braking. I believe the ignition is also being killed because the car shuts down cleanly but havent confirmed with an actual test (i.e. play with the timing light and the kill switch).

So the actual circuit could just be a normally closed switch put in series with the camshaft sensor.

Other cars might be different, that is where the wiki would be useful.

[Clev]

Originally Posted by dcb

Update, sorry this didn't sink into my head till now, but on the metro at least (and probably many other cars) YOU ONLY NEED TO INTERRUPT THE CAMSHAFT SENSOR CIRCUIT. I just ran some real world tests to confirm this. This would be a good wiki thing.

Oh, excellent idea! Does doing this trigger the Check Engine light?

[dcb]

Not on a 98 metro. But if it does on other cars then we should add a column to the hypothetical wiki table to indicate that.

[FunkSkunk]

Ok I'm lost is there a write up for 96 & newer EOC cut-off switch? Or will the original work for any year Metro? GREAT THREAD btw!!

[bbjsw10]

Originally Posted by FunkSkunk

Ok I'm lost is there a write up for 96 & newer EOC cut-off switch? Or will the original work for any year Metro? GREAT THREAD btw!!

Thanks, and I believe you could adapt this to work on 96 newer as well, or any car with enough knowledge. I may switch mine to dcb's way of the camshaft sensor. Especially when my MpGuino stuff is waiting at post office for me.

[FunkSkunk]

Sounds good! I'll have to look over my factory service manual and see where I need to splice in to make this happen! Thanks again

[hypermiler01]

Hi, I have a 1993 Metro that I am modding.

What is the benefit of cutting the injector wires, or the coil power, or the cam sensor, etc, instead of just cutting the ignition wire from the key switch?

Is there any reason I shouldn't simply install an SPST toggle switch in the ignition wire (black with blue stripe) coming from the key?

Also, can anyone tell me the purpose of the big yellow wire with the black stripe? It is currently disconnected with no apparent effects.

[MetroMPG]

Depeding on the OBD-II protocol your vehicle uses, cutting the ignition may cause a ScanGauge to shut down and take an unacceptably long time to re-initialize after you turn the power back on again. During that time, it's not recording speed/distance, and over time will skew the SG data and become a pain in the butt.

The ISO protocol in the Metros is one like this.

The other kill switch methods stop the engine witnout interrupting power to the SG, so it continues happily factoring speed/distance into the MPG calcs while instant MPG sits at "9999" (the SG value for 0 fuel use.)

[hypermiler01]

A 1993 Metro doesn't have OBD-II, does it?

[Clev]

Originally Posted by MetroMPG

Depeding on the OBD-II protocol your vehicle uses, cutting the ignition may cause a ScanGauge to shut down and take an unacceptably long time to re-initialize after you turn the power back on again. During that time, it's not recording speed/distance, and over time will skew the SG data and become a pain in the butt.

The ISO protocol in the Metros is one like this.

The other kill switch methods stop the engine witnout interrupting power to the SG, so it continues happily factoring speed/distance into the MPG calcs while instant MPG sits at "9999" (the SG value for 0 fuel use.)

Well, that and I wouldn't want to power cycle the ECU any more often than necessary...

[MetroMPG]

Good point, Clev.

---

Nope, it doesn't, hypermiler01.

I didn't know what kind of car you had when you posted your first question. You'll be wanting to build yourself an MPGuino for your instrumentation, and it's not affected by ignition-off.