M272 & M273 Engine Tumble Flap RepairBy Jason Burton
- February 26, 2016
- Hi-Line Stories
- Posted by Hi-Line Automotive
- Comments Off on M272 & M273 Engine Tumble Flap Repair
The M272 and M273 engines are incredibly robust and were the workhorse in most U.S. Mercedes models beginning in 2004. They were phased out from the U.S. market just a couple of years ago. Apart from some early engines having issues with balance shaft/timing chain sprockets, these engines are just about as bulletproof as they come. Their intake manifolds, however, have a weakness that is becoming very apparent as these engines start to get a few years on them.
First it is important to understand the intake manifolds on these engines have two sets of “runners” or paths that the air can travel as it flows into the engine with one path being shorter relative to the other. The purpose is to maximize engine efficiency depending on if the engine is operating at low or high RPM as well as based on throttle position. Through the use of a vacuum actuator flaps are moved inside the intake manifold to dictate which path the air will travel. The issue is with the linkage connecting the actuator to the flaps inside the intake. Made of plastic and forced to pivot at an unusual angle (see photos) the linkage rod has a tendency to crack. When this occurs the manifold generally uses only the longer runners. The cars on board fault system doesn’t detect an issue until the flaps become stuck “half way” drawing air from both the long and short runners. This means the engine can function sub optimally for quite a while without an error being reported to the computer and the check engine light not being illuminated.
When the flaps do become stuck in the half way position the official MB fault code is 0521 “tumble flap stuck in actuated position”, though if you are using an OBD scanner you would see the code P2004.
Mercedes does not currently sell replacement linkage and requires the purchase of a new intake manifold for approximately $1100 which will once again come with plastic linkage that can fail as the original did. Hi-Line has found that the aftermarket company URO for around $130 dollars makes a replacement linkage which is manufactured from metal permanently solving the problem and reducing the cost of parts by about $1000. Often Mercedes genuine parts offer the best quality though in unique situations such as this the aftermarket has engineered a better solution since the demand for a cost effective repair was so great.
Installation takes approximately 6 hours as the intake manifold has to be removed which also involves removing the fuel rail and many other ancillary components. Hi-Line says it is possible to inspect the linkage to see if it is damaged before a check engine light comes on and suggests doing so when the car is in for service. The inspection is slightly difficult as the air pump and other components obscure easy visual access. This is a problem that will start to affect more of these engines as they age. It is worthwhile inspecting for the issue during a Service A or B and catching it early to see if the part has failed to insure the engine is running the way MB intended it to and to insure you are getting maximum performance.