Cherokee SRT8 Forum banner

1 - 20 of 29 Posts

·
Registered
Joined
·
2,822 Posts
Discussion Starter · #1 ·
I was under the impression on the 2014 model MDS will only kick in with ECO mode on. However I have confirmed my MDS kicks on regardless of whether or not ECO is on. On the freeway MDS turns on even when in sports mode.

I noticed my Jeep would also quiet down at idle and realized it was the MDS. Is this normal?
 

·
Registered
Joined
·
2,822 Posts
Discussion Starter · #2 ·
Anyone ?
 

·
Registered
Joined
·
525 Posts
MDS is only active when ECO is on. It does not function if you have the dial turned away from Auto mode. It should still function in either transmission mode, Drive or Sport.

The variations in the engine/exhaust volumes while driving are most likely caused by the exhaust valves changing position (more open or more closed).

When stopped, it seems the engine has active idle control. When it senses you are stopped for an extended period, such as a red light, the idle will lower. This would just be to conserve fuel - along the same lines as engine start/stop systems. I don't believe MDS can function properly at idle due to the lower RPMs, but it would make sense to further conserve fuel.
 

·
Registered
Joined
·
2,822 Posts
Discussion Starter · #4 · (Edited)
MDS is only active when ECO is on. It does not function if you have the dial turned away from Auto mode. It should still function in either transmission mode, Drive or Sport.

The variations in the engine/exhaust volumes while driving are most likely caused by the exhaust valves changing position (more open or more closed).

When stopped, it seems the engine has active idle control. When it senses you are stopped for an extended period, such as a red light, the idle will lower. This would just be to conserve fuel - along the same lines as engine start/stop systems. I don't believe MDS can function properly at idle due to the lower RPMs, but it would make sense to further conserve fuel.
I have a full cat back exhaust with no valves. This is why I think my MDS is kicking on. For instance, cruising on the Freeway in Sport mode my exhaust will make that buzzing sound in 8th gear and it noticeably turns on. If I barely hit the gas it goes back to sounding normal. Then I will switch it to Auto and hit Eco and it does not make an additional sound. When I first got the Jeep you could always tell when Eco turned on by the sound distinction.

I am going to take it by the dealer and have them check it out.
 

·
Registered
Joined
·
740 Posts
I was thinking the same thing. I experienced the tone change that is similar to MDS kicking while cruising on the highway as well...

It is definitely only supposed to kick in when eco is selected and only works in auto mode.
 

·
Registered
Joined
·
2,822 Posts
Discussion Starter · #6 ·
i just contacted SRT. We'll see what they say
 

·
La Flama Blanca
Joined
·
446 Posts
MDS is only active when ECO is on.
Not trying to call you out but where did you hear this? I'm pretty sure MDS can activate on a 2014 even if the ECO button is not lit up. Pushing the ECO button makes MDS come on more than normal (along with transmission shifting early).

Copy & paste from wk2jeeps.com:
" Standard Fuel Saver Technology and a new-for-2012 active valve exhaust system allows four-cylinder operation to engage over a wider rpm range, to deliver both improved fuel efficiency - an estimated 13-percent increase on the highway - and an extended range of approximately 450 miles on one tank of gas.

Of course, even SRT owners sometimes appreciate driving more fuel efficiently. For those times, the 2014 Grand Cherokee SRT features an innovative Eco Mode that optimizes the transmission's shift schedule and expands the range of Fuel Saver Technology, which - when conditions are right - deactivates four cylinders to conserve fuel. Eco Mode is available in Selec-Track auto mode. Throttle mapping, transmission shift schedules and Fuel Saving Technology work in combination to achieve maximum fuel efficiency."

http://www.wk2jeeps.com/wk2_engines.htm

So if you are driving down the highway in AUTO non ECO Mode it will still enter MDS just on a more limited basis.
 

·
Premium Member
Joined
·
2,525 Posts
I also agree that the MDS kicks in even when the ECO is off. My ECO is never, ever on, but I can hear/feel the MDS kick in on very light throttle cruising speeds above 40mph or so. I wish they had a MDS button instead of an ECO button.
 

·
Registered
Joined
·
740 Posts
So if you are driving down the highway in AUTO non ECO Mode it will still enter MDS just on a more limited basis.
Thank you, this makes sense and would explain why it seems to come on at times. I hate to be picky but now I wish we had the option to display an indicator for when MDS does kick in...
 

·
Registered
Joined
·
2,822 Posts
Discussion Starter · #11 ·
So the dealer misinformed me!!!!??? Imagine that :D

On a serious note, at least I know I am not crazy. It would be cool if we had the option to completely disable MDS, then again, I wonder how bad the MPG would be with it completely defeated...
 
  • Like
Reactions: wanderlust

·
Premium Member
Joined
·
2,525 Posts
Woah there, Tonto. No one ever said you weren't crazy...**insert bare-ass smiley here**
 

·
Registered
Joined
·
2,822 Posts
Discussion Starter · #14 ·
Well the SRT rep got back with me and Phil was right.

Deep breath...:

"The Fuel Economy (ECO) Mode does not have any bearing on the Multiple
Displacement System (MDS) operation. These are two completely separate
features.

The Fuel Economy (ECO) mode can improve the vehicle?s overall fuel
economy during normal driving conditions.
Press the ?ECO? switch in the center stack of the instrument panel and a
green light will indicate the ECO mode is engaged.

When the Fuel Economy (ECO) Mode is engaged, the vehicle control systems
will change the following:

? The transmission will upshift sooner and downshift later.
? The torque converter clutch may engage at lower engine speeds and
remain on longer.
? The engine idle speed will be lower.
? The overall driving performance will be more conservative.
? Some ECO mode functions may be temporarily inhibited based on
temperature and other factors.

NOTE: ECO mode is only available in AUTO mode.

The Multiple Displacement System (MDS) provides cylinder deactivation
during steady-speed, low-acceleration and shallow grade climbing
conditions to increase fuel economy. The Powertrain Control Module
controls the operation of the MDS system. Primarily the engine must be
warmed up to at least at normal operating temperature. This assures the
oil is at the correct viscosity to flow to the solenoids properly. The
PCM will determine if the required engine load will permit MDS
operation.

MDS operates between 1,000 and 3,000 rpm. It will operate in
four-cylinder mode when the torque requirement is less than 95 percent
of the maximum available from four cylinders. It provides full-rated
power in V8 form with an increased fuel economy benefit when operating
in four-cylinder mode, depending on driving habits and vehicle usage. It
is integrated into the basic engine architecture and is more reliable
than add-on systems. Deactivation and activation of the cylinder is
transparent to the driver.

Deactivation occurs during the compression stroke of each cylinder,
after air and fuel enter the cylinder. Ignition then occurs, but the
combustion products remain trapped in the cylinder under high pressure,
because the valves no longer open. No air enters or leaves. During
subsequent piston strokes, this high-pressure gas is repeatedly
compressed and expanded like an air spring, but fuel is not injected.

Special hydraulic lifters are used on four of the cylinders. They are
controlled by solenoids. Each of the designated cylinders has its own
solenoid which controls two lifters. When the solenoid is energized, oil
under pressure is permitted to flow to the side of the lifter. This
causes a lock pin inside the lifter to compress. When the lock pin is
compressed the lifter contracts and its length is reduced. At its
reduced length the lifter is no longer able to open the engine valve.

Both four- and eight-cylinder configurations have even firing intervals,
providing smooth operation. Two cylinders on each bank are active when
the engine is in four-cylinder mode ? every other cylinder in the firing
order. All of the cylinders that are deactivated have unique hydraulic
valve lifters that collapse when deactivated to prevent the valves from
opening. Engine oil pressure is used to activate and deactivate the
valves. It is delivered through special oil passages drilled into the
cylinder block. Solenoid valves control the flow. When activated,
pressurized oil pushes a latching pin on each valve lifter, which then
becomes a ?lost motion? link. Its base follows the camshaft, but its top
remains stationary, held in place against the pushrod by light spring
pressure but unable to move because of the much higher force of the
valve spring.

720 degrees of crankshaft revolution is required to fire all cylinders.
This is the same for all four stroke engines. When this number is
divided by the number of cylinders, it produces, 90 for eight cylinders,
120 for six cylinders and 180 for four cylinders. Combinations of 90 and
180 work well together. The change occurs within two revolutions of the
crankshaft. When operating in the economy mode, the engine is operating
like an efficient four cylinder engine. With drive by wire there will be
no change in the accelerator pedal position.

MDS can provide a 5-20 percent fuel economy benefit when operating in
four-cylinder mode, depending on driving habits and vehicle usage. For
EPA rating purposes, fuel economy is 8-15 percent higher than if the
engine was operating on eight cylinders at all times.

MDS is integrated into the basic engine architecture, requiring a
minimum of additional parts - four additional solenoids, an oil
temperature sensor and a wire harness. Eight unique valve lifters and a
modified camshaft are also required.

Just a few simple tips can help owners of Chrysler Group engines with
Multi-Displacement System (MDS) get the most fuel mileage possible from
their 5.7L HEMI V8 engine. The customer does not need to drive in a
certain way to realize a fuel economy improvement with MDS but these
driving habits can maximize their fuel savings with this technology.

?Keeping speeds to 65 mph or below - MDS uses four cylinder mode most at
these speeds
?Use cruise control -- this helps maintain a steady speed generally
allowing the HEMI to run on four cylinders for longer periods
?Accelerate more gradually - the HEMI will provide V8 power whenever it
is requested by the driver
?Use a steady throttle whenever possible - this maximizes four cylinder
mode"
 

·
Premium Member
Joined
·
2,525 Posts
Great explanation, a-kon. Congratulatory high-fives in order hehehehe
 

·
Registered
Joined
·
525 Posts
Well, there we have it. I was misinformed by a sales person regarding MDS/Eco. Anyway, I can say I believed him because the MDS engagement/disengagement is hardly noticeable compared to some of the older Rams we have with MDS. On those, it is very noticeable when the system is active because there's no power, the engine/exhaust sounds terrible and you really have to lean into the throttle to get all 8 cylinders back.
 

·
Registered
Joined
·
740 Posts
Thanks for the confirmation @JerseyBoy just a little late to the Party!
 
1 - 20 of 29 Posts
Top