There has got to be more to it than this...

[teookie]

The GM system, or any currently produced "displacement managment" system improves highway driving by ~20%. So even if I was able to make my 2$ switch and wire system work as well as the GM versions it would only take my highway fuel economy from 17mpg to 20mpg.

That being said, since I have no control over the valves I could at best hope for a what, 5% improvement (if I'm lucky)? Looks like this has just been a fun idea, nothing more. Oh well, thanks for playing!

 

[HOUSEDIVIDED]

IMO teookie is on the right path. GM, Honda, and Chrysler's system just takes an extra step and closes the intake and exhaust valves. They still compress and decompress the same air that is still in the cylinder where the homebrew MDS system compresses new air each time. I would be interested to see if this works. I believe teookie's engine ran rough because it wasn't balanced with injectors 4, 5, 6 unplugged. It might only be possible with only 2 injectors unplugged making it a 4 cylinder instead of a 3 cylinder. This keeps the engine balanced.

 

[teookie]

Ok, so maybe pumping air through the engine is no biggie from a wasted energy standpoint, but you still have the problem of higher than normal amounts of O2 being dumped into the exhaust stream for the O2 sensors to pick up. This would cause the ECU to richen the mixture on the remaining injectors, correct? Wouldn't this negate any MPG gains?

 

[tim500]

you could just block off the egr or figuer out some way of making it close when you activate the system and since theirs so much more o2 the cat would be at alot higher temp so im sure it would still get the job done. i think in the gm and chrysler or atlest the chrysler deactivation systems they block off the oil presure to the lifters so they colapse and the valves dont open.

 

[HOUSEDIVIDED]

The richened mixture would, at the least, hurt the MPG. Some dumby O2 sensors could solve this though

 

[XJEEPER]

And now, for something different.........

http://hefleypower.com/animation1.php

 

[Nomercy]

you have a jeep cherokee, it isnt gonna get great MPGs...this is pointless IMHO and not worth the headaches youll give everyone. its been discused before use the search

 

[yj4life]

The bad part is that the cylinders that aren't firing still have a compression stroke which takes power to compress air (unless you take the spark plug out)

the dodge HEMI has something that aleviates this pressure. I think its some kind of valve. that can be turned on and off by the cars computer. It either lets the air out or cuts the oil to the lifters whch makes the intake valve stay closed or something so there is no air to compress. I haven't looked at it in a while

 

[99XJWhitey]

The HEMI opens the exhaust valve on each compression stroke and leaves the intake valve closed. It cuts the injector and the plugs still fire. although its a good idea, Im glad my 05 doesnt have MDS so I dont have to worry about tiny little springs and ball bearings breaking down inside my heads.

I seriously doubt you'll gain anything significant without a lot of money invested. You'd probably be better off pulling the 4.0 and finding a donor HEMI. mmmm XJ with a HEMI...