Diagnosing Intake Manifold Failures -

Diagnosing Intake Manifold Failures

Many owners of late-model Mercedes-Benz cars equipped with 3.0L and 3.5L V6 engines (M272 or M273) have experienced performance problems that include poor idle, loss of power and a check engine light with a P2006 code (or sometimes other codes).

Many owners of late-model Mercedes-Benz cars equipped with 3.0L and 3.5L V6 engines (M272 or M273) have experienced performance problems that include poor idle, loss of power and a check engine light with a P2006 code (or sometimes other codes).

The problem is caused by an adjustable air flap (also known as a runner or swirl flap) inside the intake manifold that breaks, resulting in unexpected and deficient performance depending on the orientation of the broken flap. These flaps move and alter the length of the intake manifold runners.

We have seen several of these intake manifold failures lately at the shop caused by the air flap that Mercedes-Benz calls a resonance manifold. As you know, the primary job of the intake manifold is to evenly distribute the combustion mixture (or the air in a direct-injection engine) to each intake port in
the cylinder head(s). Even distribution is important to optimize the efficiency and performance of the engine.

Image 1

In our example, we have a 2006 Mercedes-Benz CLK 350 (272.9 engine) with a check engine light on for multiple misfires. We have seen O2 codes as well as lean codes, so be sure to test your system correctly. Once you have completed this step, it is time to look at the manifold, paying special attention to two areas on the front of the intake. The first one is obvious. There is a lever that connects the outside runners to the center actuator (see Image 1, red outline area).

The area that is not so obvious involves the actual shafts inside the manifold (see Image 2). The shafts will fail inside the manifold and bind, causing the lever to break and the caps shown to look like they are popping off the manifold. Do not be fooled by aftermarket repair kits; they are ineffective at repairing the shafts on the inside. In the shop we have seen cases where parts of the flap became dislodged and ended up in the engine. When this happens, the technician will need to do a valve job to repair the vehicle.

Image 2

Digging In

The repair process is pretty straightforward. First, go to the engine control unit (ME-SFI) located on top of the engine, (see Image 3, N3/10). Exercise care when removing and installing the electrical connectors, and keep them safe too — they are expensive and vehicle specific.

You won’t need any special tools, so you can just get started. However, there will be hoses and seals you’ll want to order before doing the job. Over time, they get brittle and won’t be serviceable if you can get them off in one piece.

Disconnect the electrical connectors, fuel lines, air filter housing and mass air meter. I’m sure you have heard this before, but make sure nothing falls into the engine when the manifold is removed. Follow the factory instructions found in your service information system. If you follow all the steps carefully, the repair will go smoothly. Just take your time, verify the repair with a good drive cycle, and you will have properly repaired the intake manifold issue on your customer’s Mercedes-Benz.

Image 3: Courtesy of ALLDATA


Why Are Variable-Length Runner Intake Manifolds Popular?

A variable-length intake runner manifold can switch between two sets of intake runners with a flap built into the manifold. This way, there is one set of intake runners that is optimized for when the vehicle is idling and picking up low-rpm speed. Then, if the driver gets on the throttle and requests power for more demanding driving, the flap switches over to the second set of intake runners that is optimized for the higher-rpm range. Many of these intakes also have specifically shaped flaps that cause a vortex, adding even more efficiency.

The most common part to fail on the Mercedes manifold is one of the actuators for the variable system, causing the interior flap to become disconnected.

Article courtesy Import Car.

You May Also Like

Mercedes-Benz ABC Suspension

The system provides great ride & handling, but it can be complicated to service if you do not have the right training.

Mercedes-Benz’s Active Body Control (ABC) has been around since 1999. It is essentially two suspensions in one. The system uses a hydraulic cylinder on top to control the low-frequency movements of the suspension like body roll and brake dive. Below the hydraulic part is a conventional spring and dampener that can adjust rebound and compression.about:blank

ABS/ESC False Activation Diagnostics

False activation incidents involve the ABS modulator taking over braking or intervening to restore vehicle stability.

Steering Angle Sensor 101

The steering angle is used by many ADAS functions, from blind-spot detection to autonomous driving.

Throttle-By-Wire Diagnostics

On older throttle cable systems, the carburetor or fuel injection system reacted to the throttle angle.

Brake Rotor Quality Check

The brake rotor might look fine, but the problem could be internal.

Other Posts

PCV System DTC

PCV systems are far more complex now, but they are also much better at controlling crankcase pressure.

Transmission Valve Body Replacement

Learning how to perform drivetrain diagnostics and “in-the-car” repairs is important.

Adjusting Parking Brakes

You should never estimate when it comes to parking brake adjustments.

Mercedes-Benz Alignment

Here are some tips and tricks that should help you to work on just about any Mercedes-Benz from the past few decades.