When it comes to the mechanics of things I am not an expert by any stretch of the imagination, however I'm not completely dumb. This morning I though of sort of a new idea for me to save gas, by cylinder de-activation. MDS is what Chrysler uses in the Hemi engine, it shuts off a bank of cylinders by doing the following (according to the sites I have found):
1. shuts off fuel to the injector
2. no spark to spark plug
3. Keeps valves closed

So other than changing the valve stuff all it does is turn off fuel and spark. Can't anyone do that? Why not just unplug some plugs and injectors? Is there excessive wear on valves being used compared to valves not being used? What's the drawback to having valves moving without any actual combustion or exhaust? I understand that it would rob a little power from the engine if the other cylinders were still sucking and blowing air, but wouldn't you save gas at the same time? Am I missing something that is so obvious, but I didn't take into consideration when I was formulating my awesome plan at 5:30 this morning?

Also- would there be heat issues if you shut off two cylinders and run the other 4? Would it be enough to crack the head?

All I was thinking of doing is splicing in a switch that takes impulse power away from injectors and splicing in a switch into two (or three?) spark plugs. Can't be that hard right? Then how come no one has done it? I might feel dumb if I am overlooking something very crucial, but please offer your input, what do you think? I know I've unplugged two spark plugs before and the 4.0 ran just fine, what about if 3 were unplugged and you just cruise on the highway in 4th gear?

 

I just wanted to be the first to ***** because this isn't an OEM Cherokee Tech post.

Now that this was taken care of...

I think there would be more involved. My guess is the PCM will have kittens. Literally.

Baby cats will come flying out of your exhaust.

 

I should be clear- I haven't done this and I'm not fabricating anything, just unplugging stock parts on a stock motor that is mounted with stock mounts, with a stock transmission, I'm not changing anything, really.
Baby cats? So... I'll have to bring cardboard boxes with me to house the kittens in? That's not so bad... right?

 

i would say you would have enough power loss that you would be giving it more pedal to get going, plus rotating dead weight. my guess is you would get worse gas milage. the only way i could see it helping is if you wired into it a toggle switch to kill the cylinders while at crusing speed

 

Does the new Hemi actually close the valves? Seems to me that would create more resistance to the motor, were as with the valves open there would be only the mass of the "dead" piston and related parts.

And I think you'd want to turn each cylinder off in a patteren, so that every cylinder would get a chance to "not fire", and this would probably require some type of computer control. And let us not forget, you'd be droping horsepower and torque which, with the weight of the vehicle, may cause you to put your foot into the pedal more and end up using more gas. Kind of counter acting your efforts.

Just a thought

 

Good call. You'd be compressing and decompressing the air inside the cylinder.

That wouldn't be good.

 

I was just saying it'd be better in the "chat" section. That was all.

And we're talking mass amounts of kittens. Potential plague.

Kittenocolypse.

 

Disabling or deactivating the same fixed-set of cylinders for extended periods of time is definitely bad mojo in a system designed for continuous operation of all cylinders. A more effective, and perhaps less adverse, method would be a "marching disable" or a "checkerboard de-activation" pattern. In this fashion every cylinder would be treated equally and the stresses associated with the operation would be distributed for less adverse effects on the engine. This function would need to have a graduated or staged operating scheme and/or be limited to operating at the higher RPMs that correspond to highway driving. It could be implemented by way of reprogrammed/revised ECM firmware. Considering the current state of petro-economic affairs this could be an interesting challenge for an aftermarket application with significant sales potential...

 

1. shuts off fuel to the injector
2. no spark to spark plug
3. Keeps valves closed

That is basically correct but I don't think that the spark is shut off. There are 16 plugs in a new hemi and they crossfire ie: the two plugs in the same cylinder are fired by different coils. (The wires run across the intake manifold.)

http://www.asashop.org/autoinc/oct2009/techtips.htm

I can get about 22mpg out of our 2006 Hemi Durango with that system.

That being said, I wouldn't try to cobble something like that onto a vehicle that didn't have the proper engine controls to handle it.

 

It keeps all the valves closed?

Seems strange as the piston is still swinging around in there, trying to push and pull air all the time.

 

From what I read, it keeps the valves closed so that the compression can help push the cylinder back down (so in essence, help combat the energy it uses compressing in the first place). I think it might be because having the valves still opening and closing would bring in cold air which would make uneven heat distribution and rob power from the others by using up air coming in through intake for no reason. Also, a site I saw said that sometimes the exhaust valves open at the wrong time to bring in exhaust air that helps the heat distribution. But I'm not sure about that.

and also- I'm still not sure what you mean by kittens out the exhaust pipe? I'm not up on all the lingo...

 

Apart from reprogramming ECM, could you do it yourself with toggle switches inside your cabin? One toggle switch for every cylinder's spark plug and injector? That way you could turn some off and others on intermittently, or just have two toggle switches, one that turns off two cylinders and the other turns off a different two, and only have one on at once?

Also that way you could have 6 cylinders for take-off and when your on the highway you could turn off two (or even three if that's possible) from inside, and turn them all back on when you get into the city. I agree that this could be a potential temporary problem solver for people who want to combat gas prices in a gas guzzling machine

 

You'll have to be hittin those switches an awful lot.

 

If all it takes is a new smarter ECM, why isn't anyone doing this?

 

Have YOU ever engineered an ECU before?

There isn't even a pre-programmed stand alone system for our trucks.