Introduction: Understanding the M156 and Valvetronic Exhaust

The Mercedes-Benz M156 is a naturally aspirated V8 that delivers raw, mechanical character—one of the last great non-turbocharged eight-cylinders from Affalterbach. The engine responds particularly well to exhaust upgrades, but owners often seek a system that offers both aggressive tone and daily-driver civility. The Valvetronic exhaust system solves this by incorporating electronically controlled valves that alter the exhaust path, giving you quiet cruising and unrestrained V8 bellow at the push of a button.

This guide walks you through the complete installation of a Valvetronic exhaust system on an M156-equipped vehicle (C63 AMG, E63 AMG, CLK63 AMS, or S63). With methodical preparation and attention to detail, you can perform this upgrade in a home garage. Let’s cover everything from tool selection to post-installation testing.

Tools and Materials Needed

Having the correct tools on hand before lifting the vehicle prevents frustrating interruptions. You will need:

  • Socket set – Metric sizes from 10 mm to 18 mm; 13 mm and 15 mm are most common for exhaust bolts.
  • Torque wrench with a range of 10–80 N·m (for flange bolts and hanger fasteners).
  • Jack and jack stands rated for at least 3 tons – use approved lift points on the chassis.
  • Penetrating oil (e.g., PB Blaster or WD-40 Specialist) to loosen rusted fasteners.
  • Heat-resistant gloves and safety glasses.
  • Oxygen sensor socket (22 mm or 7/8 inch) if you need to remove O2 sensors from the downpipes.
  • Flare nut wrench set for any vacuum lines if your Valvetronic system uses pneumatic valve operation.
  • Dielectric grease for electrical valve connections.
  • Valvetronic exhaust system kit – verify it includes all hardware: gaskets, bolts, clamps, valve controller module, and wiring harness.
  • Trim removal tool (plastic pry bar) if you need to remove underbody panels.

Optional but helpful: an exhaust hanger removal tool, a second jack to support the exhaust during removal, and a wire brush for cleaning flanges.

Vehicle Preparation

Correct preparation ensures safety and prevents damage to the vehicle’s sensitive electronics.

  1. Park on level ground and engage the parking brake. Chock the rear wheels.
  2. Disconnect the battery (negative terminal) – the M156’s ECU may log faults if you unplug O2 sensors or valve actuators with power on. Wait 10 minutes for capacitors to discharge.
  3. Allow the exhaust to cool completely – even after a short drive, catalytic converters and pipes remain hot enough to cause burns.
  4. Remove any underbody panels that obstruct access to the exhaust (x-brace or plastic covers). Use the trim tool to release pushpins.
  5. If the vehicle has an aftermarket or lowered suspension, consider using race ramps or extra cribbing for clearance.

Removing the Factory Exhaust System

The stock M156 exhaust is heavy and often rusted at the flange joints. Take your time to avoid damaging the header studs.

Loosening and Removing Bolts

Spray penetrating oil on every exhaust flange bolt, hanger bracket bolt, and O2 sensor. Allow it to soak for 15 minutes before applying any wrench force.

  • Use the jack to support the center of the exhaust – this prevents stress on the rubber hangers.
  • Remove the O2 sensors from the downpipes if they obstruct removal. Unclip their connectors before twisting the sensors out.
  • Unbolt the exhaust from the headers – the primary flanges use nuts (usually 13 mm). A ratcheting wrench or swivel socket helps with tight access.
  • Release the mid-pipe from the rear section at the slip joint (clamp) or flange.
  • Remove the hanger isolators by pushing the exhaust side of the rubber mount off the chassis tab. Use lubricant if stubborn.

With all fasteners removed, slide the stock exhaust out from under the car. You may need to tilt the muffler section to clear the rear axle – enlist a helper or use a transmission jack for safety.

Installing the Valvetronic Exhaust System

Now the exciting part. Lay out the new components: front pipes (to headers), center section with valve housings, and rear muffler section. Verify the orientation of the valve actuators – they mount on the outside for easy access.

Fitting the Exhaust Components

Start the installation from the front of the vehicle, working your way back.

  • Install new gaskets on the header flanges. Use the provided gaskets or OEM MLS gaskets. Do not reuse old ones.
  • Mount the front pipes to the headers, loosely threading the nuts. Do not tighten yet – you need adjustment room.
  • Connect the center section to the front pipes using band clamps. Ensure the valve actuators are positioned facing outward (driver/passenger side).
  • Attach the rear muffler section to the center section. Slip all clamps loose and adjust the system to sit evenly under the car. The tips should be centered in the bumper cutouts.
  • Reinstall the hanger isolators onto the Valvetronic hanger rods. Use the original rubber mounts if they are in good condition; replace them if hard or cracked.

Connecting the Valve Control System

Valvetronic exhausts use either vacuum diaphragms or electric stepper motors. Both require proper connection to the controller module.

  • For pneumatic (vacuum) systems: run the supplied vacuum line from the valve actuator to the controller module. Avoid sharp bends and keep the line away from hot exhaust surfaces. Connect the controller to the vehicle’s intake manifold vacuum source (use the factory check valve to protect the system). If no vacuum port is available, install a dedicated vacuum pump.
  • For electronic systems: connect the wiring harness from the valve motors to the controller module. Route the harness along the chassis, zip-tying it to factory lines. Keep connectors away from direct heat. The controller typically receives power from the battery (fused) and a ground. A remote or Bluetooth module allows you to switch modes.
  • Secure the controller module in the trunk or under the rear seat (away from moisture). Use double-sided tape or a small bracket.

Final Adjustments and Torquing

After connecting all components, align the exhaust for optimal fitment:

  • Adjust tip depth and lateral position – tips should protrude evenly from the rear bumper.
  • Tighten all flange nuts to 30 N·m for the header connections (check your specific fastener). Use a torque wrench.
  • Snug down all band clamps – do not overtighten or you may crush the tubing. Most band clamps call for 15–20 N·m. Again, verify with the manufacturer’s specs.
  • Ensure no part of the exhaust contacts the underbody, driveshaft, or suspension. The system should have at least 1 cm of clearance to all moving and fixed components.

Post-Installation Checks and Testing

Before you drop the car back to the ground, perform a thorough inspection.

Inspecting for Leaks and Clearance

  • Start the engine briefly (5 seconds) with the car still on jack stands. Listen for hissing at flange joints – if you hear a leak, the torque may be insufficient or the gasket misaligned. Tighten further if needed, but do not exceed the torque spec.
  • Apply soapy water to all joints while the engine is idling. Bubbles indicate a leak – re-clamp or retorque.
  • Check that wiring and vacuum lines are not touching exhaust pipes or the driveshaft. Re-route if necessary.
  • Reinstall underbody panels and the x-brace (if applicable). Ensure exhaust hangers are fully seated.

Initial Start-Up and Valve Operation Test

Lower the vehicle, reconnect the battery, and perform a controlled start:

  • With the Valvetronic controller set to “closed” (quiet) mode, start the engine. The idle should remain smooth. If the engine stumbles or throws a check engine light, re-check O2 sensor connections and inspect for vacuum leaks (for pneumatic systems).
  • Actuate the valve to “open” mode while the engine idles. You should hear a distinct change in exhaust note. Look under the car (with a mirror) to confirm the valve flap moves freely.
  • If the valve does not respond, inspect the electrical or vacuum supply. For electronic systems, check that the fuse is installed and the remote is paired.

Road Test and Sound Evaluation

Take the vehicle on a short drive (5–10 miles) on varied roads:

  • Listen for drone at cruising speeds (around 2,000–2,500 RPM). A quality Valvetronic system should have minimal drone in closed mode.
  • Test full throttle response in open mode – the M156 should rev freely with a deep, aggressive roar.
  • Monitor any warning lights. If the check engine light appears, a scanner may show O2 sensor efficiency codes. This can happen with a less restrictive exhaust; often the ECU adapts after a few driving cycles.
  • Check that exhaust tips are not vibrating against the bumper or diffuser. Adjust if needed.

Tuning and ECU Adaptation

The M156 engine management is adaptive, but installing a free-flowing exhaust may lean the air-fuel mixture slightly at wide-open throttle. For optimal performance, consider a custom tune or a flash from a reputable shop (Eurocharged and RENNtech are well-regarded for M156 calibrations). Tuning allows you to:

  • Disable secondary O2 sensor monitoring (if you removed catalytic converters).
  • Add timing and fuel for the increased airflow.
  • Adjust idle and cold-start behavior if desirable.

If you retain factory catalysts, the ECU will likely adapt within 50–100 miles. However, a tune maximizes the gains from your Valvetronic system.

Maintenance Tips for Longevity

Your Valvetronic exhaust requires minimal upkeep to deliver years of trouble-free operation.

  • Lubricate valve pivots every 12 months or 10,000 miles with high-temperature grease (copper or moly-based). A stuck valve can cause remote operation failure or uneven exhaust flow.
  • Clean electrical connectors with contact cleaner and apply dielectric grease when servicing.
  • Inspect hangers and clamps annually – rubber mounts can fatigue, causing rattles. Replace as needed.
  • Wash exhaust tips with a non-abrasive metal polish to prevent pitting from road salt and brake dust.
  • Check for exhaust leaks whenever you hear a change in sound – early detection saves expense.

Conclusion

Installing a Valvetronic exhaust system on the M156 is a rewarding upgrade that transforms your Mercedes AMG into a dual-personality machine: refined and quiet for daily commuting, then ferocious and thrilling when you open the valves. By following this step-by-step guide—with careful attention to fastener torques, valve control routing, and post-installation testing—you ensure a reliable, leak-free installation that lets you enjoy the full character of the M156 for years.

For additional reference, consult the official Valvetronic website for model-specific instructions, and join community forums like MBWorld AMG forums for tips from other owners. If you encounter stubborn fasteners during removal, a detailed guide on Pelican Parts illustrates common solutions for Mercedes exhaust work.