How to Disable MDS on Hemi: Complete Guide for Better Performance

Tired of your Hemi engine shifting between 4 and 8 cylinders? You’re about to discover exactly how to disable MDS on your Hemi engine. This guide covers everything from quick temporary fixes to permanent solutions that’ll give you full V8 power all the time.

What is MDS on a Hemi Engine?

The Multi-Displacement System (MDS) in your Hemi engine automatically shuts down four cylinders (1, 4, 6, and 7) during light driving conditions. When you’re cruising on the highway or in low-load situations, the system closes these cylinders’ intake and exhaust valves to save fuel.

While Chrysler designed this technology to improve fuel economy, many Hemi owners find the constant switching between 4 and 8 cylinders creates issues like:

• Uneven engine response
• Annoying exhaust drone
• Potential long-term reliability problems
• Inconsistent power delivery

Why Disable MDS on Your Hemi?

Before diving into the “how,” let’s talk about why you might want to disable MDS:

Performance Benefits

When you disable MDS on your Hemi, you’ll immediately notice:

• More consistent throttle response
• Elimination of the hesitation when transitioning between 4 and 8 cylinders
• Smoother power delivery throughout the RPM range
• More predictable acceleration

Reliability Improvements

Many Hemi owners report these long-term benefits:

• Reduced wear on valve train components, especially lifters
• Lower risk of lifter roller failures that plague MDS systems
• More consistent engine temperatures
• Prevention of valve seat degradation

Better Driving Experience

Beyond the mechanical advantages, you’ll enjoy:

• Elimination of the distinctive MDS exhaust drone
• More engaging V8 sound at all times
• More responsive feel when pressing the accelerator

Temporary Methods to Disable MDS

Want to try turning off MDS without permanent changes? Here are your options:

Using Gear Limitation

This super-simple method works on most Ram trucks and other Hemi-powered vehicles:

1. Start your vehicle
2. While in Drive, use the +/- buttons on your steering wheel
3. Manually limit your transmission to its highest gear (8th gear on 8-speed models)
4. The ECM will keep all cylinders active to maintain power in the higher gear

Pro tip: This method immediately disables MDS but resets every time you shut off your vehicle. You’ll need to repeat these steps after each restart.

Activating Sport Mode or Tow/Haul Mode

Another easy temporary fix:

1. Locate your drive mode selector or dedicated Tow/Haul button
2. Engage Sport mode or Tow/Haul mode
3. The performance-oriented shift logic in these modes prevents MDS from activating

This method works better on some models than others. The 8-speed transmission may still require the gear limitation step mentioned above for full effectiveness.

Permanent Software Methods to Disable MDS

Ready for a more lasting solution? Let’s look at software options:

Using Aftermarket Tuners

For a permanent software fix that doesn’t require mechanical work:

1. Purchase a compatible tuner (DiabloSport, Superchips, HP Tuners, etc.)
2. Connect the tuner to your OBD-II port
3. Select the “Disable MDS” option in the tuner’s menu
4. Upload the modified tune to your vehicle’s ECM

Popular tuners and their features:

• DiabloSport Trinity: User-friendly interface, multiple tune options
• Superchips Flashcal: More affordable, basic tuning capabilities
• HP Tuners VCM Suite: Professional-grade tuning, requires more technical knowledge

Advanced ECM Reprogramming

For those comfortable with more technical software:

1. Use HP Tuners VCM Suite to extract your current ECM tune
2. Navigate to the Engine > Fuel > Lean/Fuel-Saving section
3. Locate and disable the MDS enable parameter
4. Save your modified tune
5. Reflash your ECM with the updated tune

This method gives you the most control but requires more technical knowledge than plug-and-play tuners.

Permanent Mechanical Methods to Disable MDS

For the most comprehensive solution, consider these mechanical options:

Installing an MDS Delete Kit

Companies like Melling offer complete MDS delete kits that replace the hardware components:

1. Remove your ECM and send it for unlocking to disable MDS software flags
2. Replace the MDS lifters with standard lifters
3. Install block-off plugs in the solenoid ports
4. Add a delete camshaft if included in your kit
5. Verify pushrod length and retime the engine

This option requires significant engine disassembly and should be performed by an experienced mechanic or engine builder.

Components in a Typical MDS Delete Kit:

• Non-MDS lifters
• Lifter trays
• Solenoid block-off plugs
• Sometimes a revised camshaft
• Gaskets and seals

The cost ranges from $500-1,200 for parts alone, plus labor if you’re not doing the work yourself.

Phaser Limiter Kits

If you’re planning cam upgrades along with MDS deletion, consider a phaser limiter kit:

1. Install a kit like the COMP Cams Phaser Limiter
2. This restricts variable valve timing movement to 14 degrees
3. Prevents valve overlap conflicts with aftermarket cams
4. Note: You’ll still need to disable MDS through software

These kits work with 5.7L, 6.1L, and 6.4L HEMI engines and complement other mechanical MDS deletion components.

Comparing All MDS Disable Methods

Here’s a comprehensive comparison to help you choose the right method:

Important Considerations Before Disabling MDS

Before making any changes to your Hemi, consider these factors:

Warranty Implications

• Temporary methods like gear limitation or drive modes don’t affect your warranty
• Software tuning may be detected during dealer service and could cause warranty issues
• Mechanical modifications will almost certainly void your powertrain warranty

Fuel Economy Impact

Expect a decrease in fuel economy after disabling MDS. Most owners report:

• 1-2 MPG reduction in highway driving
• Minimal change in city driving (where MDS rarely activates anyway)

Emissions Compliance

In states with strict emissions testing, be aware that:

• Software tuning may trigger check engine lights
• Some tuners offer emissions-compliant modes for testing
• Mechanical modifications might create emissions compliance issues

Enhanced Oil System Recommendations

If pursuing mechanical deletion, consider these upgrades:

• Install a high-volume oil pump (like the Melling 10452)
• Switch to a higher-quality synthetic oil
• Consider shortened oil change intervals

Real-World Results From Disabling MDS

Many Hemi owners report these outcomes after disabling MDS:

• Smoother acceleration across all driving conditions
• Elimination of the distinctive “MDS drone” from the exhaust
• Better throttle response, especially during highway passing
• More consistent engine temperature
• Reduced hesitation during acceleration
• Some report fewer long-term issues with lifters and other valve components

Many owners find the improvements in drivability outweigh the slight decrease in fuel economy.

Steps to Choose Your MDS Disable Method

Not sure which approach is right for you? Follow this decision path:

1. Try a temporary method first to see if you like the feeling of MDS-free driving
2. Consider your technical comfort level and warranty concerns
3. Set a budget for your MDS disable project
4. If you want permanence without mechanical work, choose a tuner
5. If you’re planning other performance upgrades, consider a complete mechanical delete

The best method depends on your specific goals, technical ability, and budget.

The Easiest Solution for Most Hemi Owners

For most Hemi owners, an aftermarket tuner offers the best balance of:

• Relatively straightforward installation
• Permanent results
• No mechanical disassembly required
• Additional tuning options beyond MDS disable

Products like the DiabloSport Trinity or Superchips Flashcal offer user-friendly interfaces that make the process accessible even to those with limited technical knowledge.

By disabling MDS on your Hemi, you’ll transform your driving experience with more consistent power, improved reliability, and the full-time V8 sound that made you choose a Hemi in the first place.