The HEMI MDS Guides 5.7 and 6.4. Cylinder deactivation technology is used in some modern performance engines, such as the 5.7 and 6.4 HEMI. This improves fuel economy and reduces pollution. It contributes to these huge V8 engines meeting today’s tighter emissions rules. Cylinder deactivation appears simple in theory, but there is a lot that goes into it. In this article, we explain 5.7 and 6.4 HEMI MDS, look at some pros and cons, and talk about MDS difficulties and delete kits.
Which Models Make Use of MDS?
MDS technology is used in the majority of 5.7 and 6.4 HEMI engines, including the following:
- Chrysler 300C 2005+
- Chrysler Aspen 2007+
- Jeep Grand Cherokee 2005 and after
- Jeep Commander 2006 and after
- Dodge Magnum 2005 and after
- Dodge Durango 2006 and later
- Dodge Charger 2006 and after
- Dodge Challenger 2009+
- Dodge / Ram 1500 2006+
The 5.7 and 6.4 HEMIs with manual transmissions are an exception. MDS is not used in conjunction with the handbook. Furthermore, MDS is not used in Ram 2500 and 3500 pickups. The 6.1 HEMI in previous SRT models, as well as the 6.2L Hellcat engine, do not have MDS. Otherwise, the technology is available in either of the 5.7L or 6.4L HEMI automatic transmissions stated above.
What Exactly Is HEMI MDS?
In its most basic form, Chrysler HEMI MDS is cylinder deactivation technology. MDS is an abbreviation for Multi-Displacement System. Some GM engines have a similar system known as Active Fuel Management (AFM). Both systems are designed and operated in very similar ways. However, in this post, we will just look at the 5.7 and 6.4 HEMI MDS.
In certain scenarios, like as driving at a constant pace, MDS turns down four of the V8’s cylinders. When MDS is turned on, the V8 HEMI effectively becomes a 4-cylinder engine. When you need power and press the throttle, the MDS re-ignites the cylinders, giving you full power from the huge 5.7L and 6.4L engines.
Sounds easy, doesn’t it? The Multiple-Displacement System, on the other hand, is more complicated than merely turning off the ignition. For MDS to function well, a lot of events must occur in quick succession.
How Does MDS Function?
The easiest technique to cylinder deactivation appears to be to turn off the ignition and fuel supply. That would be as simple as a short tune tweak and would not necessitate any special technology. However, this would offer no actual improvement in terms of fuel economy or emissions.
When all four cylinders are turned off, the engine still needs to provide the same amount of power to maintain a constant speed. As a result, once the others are turned off, the remaining cylinders require more air and fuel. The advantages of cylinder deactivation stem mostly from reduced pumping losses.
This means you must maintain the intake and exhaust valves closed at all times. First, the ECM reduces gasoline to the shutting-down cylinders (MDS deactivates cylinders 1, 4, 6, and 7). The intake valve then opens for the final time to draw in air before being closed by the ECM. On the power stroke, no ignition happens, and the exhaust valve opens for the final time before being shut down. This occurs in a fraction of a second, all while the ECM commands more throttle and fuel for the remaining four cylinders. The entire process takes one to two tenths of a second, depending on RPM.
How do you close the valves while the cams continue to rotate normally? MDS solenoids are used in the Chrysler 5.7 and 6.4 HEMI engines to supply pressurized oil to a locking pin in the lifter. The locking pin permits the lifter roller to move in accordance with the cam profile. However, because the motion is not transferred to the plunger, the pushrods are not engaged. MDS operates primarily through specific lifters and solenoids, with the ECM ensuring that the process runs smoothly.
Pros of Chrysler HEMI MDS
The following are some advantages of the 5.7 HEMI Multi-Displacement System:
- improved fuel economy
- Reduced emissions
The benefits of MDS are straightforward. It improves fuel economy and reduces pollutants. As previously stated, MDS does not enhance fuel economy due to four fewer cylinders receiving fuel. It is instead owing to lower pumping losses. When the throttle is opened farther, the engine becomes more efficient.
By turning off four cylinders, the engine must open the throttle nearly twice as much to produce the same amount of power. This is where the 10-20% MPG boost comes from.
Cons of the HEMI Multi-Displacement System
MDS, unfortunately, has certain potential drawbacks:
- More components are likely to fail.
- cylinder temperatures that are lower
The HEMI employs four MDS solenoids, which means four solenoids that could fail. The locking pins in the lifter rollers are another component that can fail. The point is that more moving parts equals more things that might go wrong, which we’ll go into in the next section. Before delving into the 5.7 HEMI MDS issues, it’s crucial to consider another potential disadvantage.
MDS always turns off the same four cylinders: 1, 4, 6, and 7. Assume you’re driving at a constant speed on a relatively flat route for an extended period of time. Those cylinders and surrounding surfaces (such as the head) will become substantially cooler. When you suddenly require a lot of power, the cylinders re-ignite at high rpm and engine load. Extreme heat changes and loads are not desirable.
MDS is meant to restart the cylinders every so often to keep them from losing too much heat, which alleviates some of the problems. Many HEMIs enjoy long lives with little drawbacks. However, it can still result in uneven cylinder wear. It’s not necessarily bad for the engine, but it’s also not ideal.
6.4L and 5.7L HEMI MDS Issues
The majority of the concerns with 5.7 and 6.4 HEMI MDS were briefly discussed in the previous section. In the next sections, we’ll go over some of the most prevalent MDS difficulties. Then we go through MDS delete choices, which are becoming more popular as older HEMIs age and develop MDS issues. In any case, some of the most common HEMI MDS issues are as follows:
- Solenoids
- Rollers for the elderly
- Seats for valves
Before we begin, it’s crucial to understand that none of these problems are particularly frequent. Instead, when 5.7 or 6.4 HEMI MDS-related issues do develop, these are a few common locations to look into. MDS has been around for quite some time and has proven to be quite dependable. However, issues are not unheard of, and there is a reason why some HEMI owners uninstall the Multi-Displacement System.
1) HEMI MDS Solenoid Problems
Despite the fact that HEMIs employ four solenoids, this is a rather common problem, so we’ll go quickly. Failures of MDS solenoids can and do occur. Because the sensors receive an electronic signal from the ECM, electronic faults can occur. Oil that is dirty or polluted can potentially clog sensors and cause problems.
Again, this is not a frequent MDS issue. The MDS solenoids, on the other hand, are located beneath the intake manifold. Replacing the solenoids is quite straightforward, but it does necessitate some effort. A single solenoid costs around $50. However, if you go to a repair shop, labor can cost between $400 and $600. It’s often better to replace all of the sensors (especially on older, high mileage HEMIs) because they’re very cheap in comparison to the labor.
2) Lifter Roller Failures on 5.7 HEMI MDS
The most common MDS-related problem on this list is lifter and lifter roller difficulties. These issues are commonly addressed on the 5.7L and 6.4L HEMI since they can be expensive and potentially lead to engine failure. The primary cause is oil contamination.
If small bits of dirt or debris obstruct the circuit to the locking pin, the lifter may fail to change status, move slowly, or fail to change completely. The roller will then continue to follow the cam lobe until it can no longer. The 5.7/6.4 HEMI roller then comes into touch with the camshaft lobe. Contact between metals harms the lifter, lifter roller, and camshaft. Metal shavings can get through the oil filter and cause further harm in rare situations (if not identified early enough).
In the best-case scenario, you’ll be replacing the camshaft, lifters, and lifter rollers. This is all done beneath the cylinder head, so it’s a time-consuming task. The cost of parts also adds up quickly; this job is likely to cost $1,500 or more at a repair shop.
3) Dropped Valve Seats & Multi-Displacement System
Dropped valve seats are the least common issue on this list, affecting primarily the original 5.7 HEMI (before to its upgrade to the 5.7 Eagle in 2009). This issue, however, underlines the previous concern about cooler temperatures on MDS cylinders.
After a long drive in which MDS is active for longer periods of time, those cylinders are much colder. You then, for example, stop at a gas station to fill up on gas before restarting the engine. The diameter of the valve seats would shrink quicker than the aluminum cylinder head. As a result, the valve seats may drop.
This affected some MDS HEMI engines from 2005 to 2008, but problems were uncommon even then. The newer 2009+ 5.7 Eagle has a design that keeps the valve seats in place, which eliminates the problems. Nonetheless, it serves as a warning that MDS has certain inherent limitations due to changing cylinder and head temperatures.
Related : The Guide to LS6 Camshaft Upgrade
HEMI MDS Delete 5.7 & 6.4
In the performance and aftermarket Mopar world, removing the 5.7 and 6.4 HEMI MDS is typical. MDS, while generally dependable, does not provide any major benefit other than improved MPG. If you don’t care about fuel economy, it merely introduces the chance of malfunctions and other issues.
MDS may be removed in two ways: disable it or entirely erase it. A simple tuner will allow you to deactivate the MDS system and instantly reactivate it if desired. Otherwise, MDS deletion kits are available to completely remove the Multi-Displacement System.
MDS deletes necessitate the use of non-MDS lifters and retainers, as well as four plugs to replace the solenoids. Because most aftermarket cams are non-MDS, this is normal procedure for camshaft modifications. If you encounter major HEMI MDS issues (such as the lifter rollers), it may be a good idea to totally remove the system.
