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  #13  
Old 02-04-2011, 09:21 AM
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Re: 5.7 L ECO quesstion

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Originally Posted by 2011RitterGC View Post
Why?? If you are "turning back on" 4 cly why would it matter which 4?
I think you mean "Why does it make a difference between alternating cylinders and "lighting" them every few seconds?"

If you are alternating cylinders, then EACH rotation you have to switch one back to the next. So, as RPMs increase, the time you have to inflate the lifter goes down. Less than .02 seconds at 3000 RPM, for instance. Inflating a hydraulic lifter is NOT that fast.

If you "light" them every 10 seconds, you can just inflate the lifters for a second, and not really care about how many revolutions that amounts to.

This is based on what NetJunkie said -- "...4 fires, then on the next cycle the other 4 fire."
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Old 02-04-2011, 09:35 AM
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Re: 5.7 L ECO quesstion

[/QUOTE] If you are alternating cylinders, then EACH rotation you have to switch one back to the next. So, as RPMs increase, the time you have to inflate the lifter goes down. Less than .02 seconds at 3000 RPM, for instance. Inflating a hydraulic lifter is NOT that fast.

If you "light" them every 10 seconds, you can just inflate the lifters for a second, and not really care about how many revolutions that amounts to.

This is based on what NetJunkie said -- "...4 fires, then on the next cycle the other 4 fire."[/QUOTE]

No I was talking about each time it when in and out of ECO mode, not each ten sec. As long as it is in ECO mode the same 4 are off. Next time it goes into ECO mode the other 4 turn off. Sounds like it does not work this way but it could.
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Old 02-04-2011, 09:42 AM
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Re: 5.7 L ECO quesstion

Well, that's not what NetJunkie said, which is that to which I was referring.

Your speculation, that they COULD alternate each time it enters ECO mode I agree with. It could, and my argument doesn't have a bearing on that. I still believe Voyager, though.

B
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Old 02-04-2011, 10:53 AM
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Re: 5.7 L ECO quesstion

Which four shut down doesn't really make a difference. Whether it's the same four or alternating. The firing of the cylinder is the only difference in wear essentially.

All of the pistons are still moving up and down the bore wearing the rings, cylinder walls, piston skirts and bearings. So MDS is not intended to "save" wear on the cylinders which are shut down. Also the active cylinders recieve no additional wear. The only appreciable difference in wear between the active and non active cylinders might be at the rod bearings due to less pressure on the "power" stroke of the de-activated cylinders. With bearing technology what it is today along with tolerances and advances in oil this is also negligable.
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Old 02-04-2011, 11:38 AM
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Re: 5.7 L ECO quesstion

Is there a way to electronically disable the MDS system? I am kind of curious to see what kind of fuel mileage/MPG difference there would be in real world driving with the MDS functioning as designed, and then try another tank with the system turned off.
The idea behind MDS is nice but is it really that effective in the Jeep that it warrants how much more complicated of an engine it is?
Any ideas on this?

James
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Old 02-04-2011, 11:46 AM
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Re: 5.7 L ECO quesstion

There's no separate fuse for it. It might be possible to disable it through the CAN-BUS, but you'd need to have the dealer diag tool or equivalent.

Of course, you could always hot-wire the solenoids, but I don't think you want to go that far
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Old 02-04-2011, 12:47 PM
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Re: 5.7 L ECO quesstion

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Originally Posted by JTS97Z28 View Post
Is there a way to electronically disable the MDS system? I am kind of curious to see what kind of fuel mileage/MPG difference there would be in real world driving with the MDS functioning as designed, and then try another tank with the system turned off.
The idea behind MDS is nice but is it really that effective in the Jeep that it warrants how much more complicated of an engine it is?
Any ideas on this?

James
I believe the tuners like SuperChips and Diablo do just that through the ECM reprogramming. Of course all the other settings are optimized for performance so it wouldn't be an apples to apple comparison for mileage.
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Old 02-04-2011, 12:59 PM
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Re: 5.7 L ECO quesstion

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Originally Posted by parker View Post
The only appreciable difference in wear between the active and non active cylinders might be at the rod bearings due to less pressure on the "power" stroke of the de-activated cylinders. With bearing technology what it is today along with tolerances and advances in oil this is also negligable.
Yes, and the fact that when the cylinders shut down they hold the full combustion stroke pressure which maintains a load on those components. It's good to know the shut-down-cylinders are re-lit on a set interval; the stored pressure in those cylinders would eventually be purged (the normal cylinder pressure leak down) so re-firing on an interval basis helps hold a steady pressure and smoother (not necessarily smooth) running engine in 4cyl mode.

OT Note: I believe it is a mechanical problem in the MDS operation that causes the shuddering issue in some vehicles. If that cylinder pressure is not maintained in the shut-down cylinders, the free floating components and the inherent imbalance from the other four cylinders firing would make a ripe environment for significant shuddering.
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