@Wild one, Do you have a source for "cutting flow to the lifters"? My understanding of it's function is that the solenoid opens the bleed port on the lifter which essentially stops the lifter from pumping up thus stoping in from actuating the valves. The oil supply to the lifter doesn't change.
Source:
- Then the computer opens the MDS solenoid which supplies oil pressure to the lifter deactivation ports.
- This oil pressure passes through the hole in the side of the lifter and decouples the inner plunger from the lifter body. This “deactivates” the lifter.
- The deactivated lifters will not open the valves. However, enough pressure is left to keep the pushrods from rattling and the lifter following the cam.
Multi-Displacement System (MDS) valves deactivate 4 of the 8 lifters in a (V8) cylinder system when the throttle is closed or in cruise mode at low RPM. The purpose of this feature is to enhance the fuel economy available to the HEMI engines introduced by Chrysler. ALL Mopar models 2005+ are...
10secondracing.com
The solenoids aren't anywhere near the lifters,and aren't close enough to the lifters to activate any part of the lifter,the solenoids provide more oil flow to push the pins in,to release the lifter body from the lifter plunger
This is right from your article,as you can see the solenoids open and provide more oil to the lifters to deactivate or push the pins in on the side of the lifter body,which lets the MDS lifters collapse .To activate MDS mode,the solenoids have to provide more oil to the lifter gallery.
- The computer shuts off fuel to the MDS controlled cylinder.
- Then the computer opens the MDS solenoid which supplies oil pressure to the lifter deactivation ports.
- This oil pressure passes through the hole in the side of the lifter and decouples the inner plunger from the lifter body. This “deactivates” the lifter.
- The deactivated lifters will not open the valves. However, enough pressure is left to keep the pushrods from rattling and the lifter following the cam.
- Since no air can get in or out, the engine is running on the remaining four cylinders. The deactivated cylinders act like air springs. This keeps the engine running smoothly and minimizes pumping loss.
From farther down the article.
Cutaway version of a Hemi MDS lifter. The key thing here is the transverse pin exposed to oil pressure from the orifice in the lifter body. As the fluid circuit energizes, the pin is pushed in, unlocking the plunger inner body from the lifter's outer body. In this manner, the roller tip can follow the cam lobe without the plunger moving the pushrod up and down.
The lifter valley of a stock 5.7L Hemi without MDS. Notice the two white plugs next to the cam tunnel? These are where the MDS solenoids would normally go. Truck engines like this one were not equipped with MDS, and had these plugs instead.
Photo by Douglas Glad.
This is the MDS solenoid that plugs into the lifter valley in four holes adjacent to the cam tunnel. These go where the blank plugs were shown in an earlier photo of the lifter valley.
Photo by Dave Young.
At first glance, this replacement Dorman MDS lifter transducer looks like an injector, as many of its parts act similar to an injector's. These often get clogged with particles from the oil. When that happens, the lifters can fail if the solenoid is not replaced.
Getting cylinder deactivation to happen from a practical standpoint takes some pretty precise engineering. Within the lube circuit of the Hemi's hydraulic roller lifters are four control valve solenoids that when energized by the ECM through the harness divert pressurized oil to a locking pin in the lifter. When this pin is pushed into the body of the lifter, the roller on the lifter can still follow the cam profile, but the motion is no longer translated to the plunger
—the part of the lifter that engages the pushrod. When the ECM de-energizes the solenoid, the spring-loaded pin engages with the plunger and all the parts of the lifter have the same motion again.
A few things can happen that can cause this mechanism to break down, the most common of which is oil contamination. When small pieces of dirt block the lube circuit, the lifter may not be able to change state, or the change may happen slower, or only partially. A common scenario with the MDS system in Hemis is where the ECM believes the lifter is engaged at higher rpm when it is not. Here, the internal pin that locks the lifter body to the plunger is still disengaged when the engine rpm goes up. In this failure mode, the roller follows the cam lobe, until it reaches an engine speed where it can't, and the roller crashes repeatedly on the lobe. Eventually, the lifter, roller, needle bearings, and the lobe surface become damaged to the point of failure.
And then there's also this video,that goes into a good explanation of how the MDS system works,and the differance in the MDS block off plug,and the MDS solenoid. Towards the end of the video,he talks about the factory MDS block-off plugs.
I feel like MDS has been unfairly made the culprit for the lifter failures we see on Gen 3 Hemi engines. In this video I explain exactly how the system works...
www.youtube.com