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2018 Scat Pack SHAKER in Plum Crazy
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The problem with those 8-6-4 wasn't the deactivation tech, it was the fuel tech at the time, and the fact that in 8 cyl mode it was barely adequately powered.
 

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The problem with those 8-6-4 wasn't the deactivation tech, it was the fuel tech at the time, and the fact that in 8 cyl mode it was barely adequately powered.
This was 1981, the worst decade for horse power(in the modern scheme of things). At least they gave it the boot after one year of trying. It was an out of the box concept though, I have to give credit for that.
 

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Cadillac used these mechanical solenoids (through the valve rocker cover) that deactivated the rocker.

The processor (this was very early electronics of 1981) didn't work effectively to make those transitions from 8 to 6 to 4 cylinder operation (depending on load / demand on engine) and it would tend to "hang" and not revert back 8 cylinders when the driver needed it, adding to driveability issues.

The other part is 140hp (yes that low) pulling around full size Cadillacs...by comparison many N.A. 4 cylinder engines today outdo what that 6.0 liter Caddy V8 could put out.

Imagine it chugging in 4 cyl mode and pressing on the throttle and it doesn't change back into 8 cyl mode. That thing would have fallen on its face!
 

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To the OP, I recently went back to the 392 from the 5.7L, your description in your original post about MDS is both accurate & normal. The 392 will not engage MDS nearly as often, that's the intended strategy in street mode.

If you put the 392 in ECO mode it'll behave a lot more more like the 5.7 and engage (over-engage, in my opinion) MDS. If you like the associated exhaust drone ;)
 

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srobinson, that car is freaking beautiful.
That is all.
 

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It shows on the DID. You have to toggle to the MPG gage, and in the center of the gage is where it will display when it's active.
 

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987394


A Guy
 

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Hey guys, Im new here and just made the jump from a 2017 R/T 5.7 to a 2018 R/T scatpak 392, both of which have MDS. What I noticed and am concerned about is that the 5.7 was much more MDS friendly, in the sense that it would engage as soon as it could and stay on for as long as possible. The 392 on the other hand rarely ever engages MDS, even when it does, all it takes is the slightest press on the throttle to disengage it. I know MDS isn’t a desirable feature for most people here, but I use my car as a daily driver and can benefit from even the smallest gains in fuel economy. My questions are:

1) Is this a sign of the MDS failing or is it normal?

2) How should I look out for now that I own a 392? (What are some common failures and problems with the engine or trans)

3) I’ve read on many places that the 6.4L is much more reliable compared to the 5.7L, is this true?

My vehicle is a salvage but was repaired to factory specs, it has 15K miles on it. Thank you!!
I have owned a 15 R/T and then a 16 scat. Mine did the same thing. I did not like the MDS kicking in
so easily on the 5.7. So I kept it in sport most of the time. I would let both motors engage the MDS
when on the interstate though.
 
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