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

http://ecomodder.com/forum/showthrea...html#post50928


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.