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  Tech Tips

How Chrysler's Multiple Displacement System Works

Posted 10/12/2009
By Greg Montero

In 2005, the Multiple Displacement System (MDS) version of the 5.7L HEMI engine was introduced on the Chrysler 300C and Dodge Magnum. This engine can deactivate four of the eight cylinders, and operate as a 4-cylinder engine during periods of low load, improving fuel economy and emissions. The MDS provides the 5.7L engine the fuel economy of a V6 while maintaining the performance of a V8. The fuel economy improvement is estimated to be up to 20 percent, depending on driving conditions. The MDS operation, invisible to the driver, is fully integrated into the fuel injection system.

"In 2005, the Multiple Displacement System (MDS) version of the 5.7L HEMI engine was introduced on the Chrysler 300C and Dodge Magnum. This engine can deactivate four of the eight cylinders, and operate as a 4-cylinder engine during periods of low load, improving fuel economy and emissions.”

When the MDS engine switches to 4-cylinder mode, the powertrain control module (PCM) controls solenoids that manage special "dual mode" lifters, allowing the intake and exhaust valves to remain closed on cylinders 1, 4, 6 and 7. There is one solenoid for each cylinder (two lifters). The PCM also deactivates the fuel injectors for these cylinders when in the 4-cylinder mode.

When the MDS solenoids are in the "off" state (8-cylinder mode), they supply oil pressure of approximately 3 psi to the lifter bores. This lifter oil keeps the bores lubricated and prevents air from entering the system. When the solenoids are activated, oil pressure of 16 psi or greater is supplied to the lifters and the engine enters the 4-cylinder mode.

When the special lifters are supplied high oil pressure by the solenoid, pins inside the lifter move inward. This unlocks the outer portion of the lifter and allows it to move independently from the center portion of the lifter. The camshaft can move the outer portion of the lifter without transferring motion to the inner portion of the lifter.

8-cylinder mode: Solenoids are in the "off" state (de-energized). Minimal oil pressure is applied to the special lifter. They are working normally in this mode.

4-cylinder mode: Solenoids are in the "on" state (energized). High oil pressure is applied to the special lifters and the lifters become inactive and essentially the four pistons are along for the ride. Both valves are closed.

The PCM will activate the 4-cylinder mode when the following enabling conditions are met:

  • Low engine load

  • 1200 to 3000 rpm

  • Vehicle speed between 12 mph and 90 mph

  • Battery voltage from 9 volts to 15 volts

  • Oil pressure from 15 psi to 147 psi

  • Oil temperature greater than 120 F

  • Engine coolant temperature from 158 to 248 F

  • Ambient temperature from 14 F to 248 F

  • No throttle position sensor or MDS faults

The PCM deactivates solenoids one cylinder at a time in the firing order. If the system is "on" for long periods of time, such as a long flat road with no stopping, the system will return to the 8-cylinder mode approximately every six minutes to maintain engine temperature. The PCM will also unlock the torque converter before the transition, to minimize the effect on driveability.

The oil temperature sensor used for this system is a two-wire sensor, negative temperature coefficient, like the sensors for engine coolant temperature or intake air temperature (IAT). The PCM uses this input - along with oil pressure, load and rpm - to calculate oil viscosity and flow rate. This information is critical to MDS operation.

It's important to know this engine uses 5W-20 engine oil. If the wrong oil is used, fault code P1521 can be set, and the vehicle may show symptoms of a shudder - similar to a torque converter shudder - when the MDS system is activated and deactivated. Other symptoms may include MDS performance codes or engine misfire codes.

Before spending a lot of time with these codes, use the vehicle service history to find out what type of oil is in the engine. Because this is not always possible, the next best thing is to replace the oil (and filter) with 5W-20. This may have to be done twice to fully restore the system back to normal. Oil sludging, restricted oil passages or lifter contamination can also cause problems with this system.

Quick facts:

  • Each MDS solenoid has about 12 ohms of resistance. When the solenoid is activated by applying 12 volts to it, an audible "click" can be heard from under the intake manifold. This test can be done with a jumper wire or by using the actuator test mode (ATM) mode of a compatible scan tool.

  • If the solenoid is mechanically stuck in the "on" position, the result will be one dead cylinder.

Hopefully, this information will be helpful if one of these systems shows up in your shop.

Greg Montero Greg Montero, AAM, is an Identifix Chrysler team leader. He is an ASE master with L1 certification.
Experience Identifix This information is provided by IDENTIFIX®. IDENTIFIX® resources cut diagnostic time and provide repair solutions that increase the shop's bottom line. From Repair-Trac pattern failure quick fixes, to Diagram-Online wiring diagrams by fax, to the Repair Hotline staffed by 32 master techs who specialize in diagnosing complex problems by phone or fax, IDENTIFIX® helps techicians fix more cars in less time.

For more information on IDENTIFIX, call (800) 288-6210, 8 a.m. - 6 p.m. Central Time.

www.identifix.com.

© 2011 IDENTIFIX. All Rights Reserved.

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