PCV Diagram
Every engine I've ever seen has a routing to the intake manifold, and to the inlet; basically pre and post throttle body. This is to you're pulling maximum vacuum and drawing fresh air into the crankcase when not under load. The PCV valve is what switches from one loop to another; load/no-load.
Anyone have a FSM or system diagram?
There are two variations of the M156 intake manifold and the breather valves.
1- Engines up to 60000591 Have a unique intake manifold part #. This was the original part on my ML63. In this configuration, crank pressure enters the intake manifold through two entry points:
A- Pre-Throttle body at atm. pressure regulated by the throttle plate position = Full load breathing
B- Post-throttle body at manifold vacuum open at all times = Part load breathing
As the diagram below shows.
My ML63 suffered from an increase in crankcase pressure. Oil dipstick would pop-out after load and oil would leak from the seals. Since the old-design breather pipe does not wear out like the newer PCV design, there was nothing to do but to replace the intake manifold to the newer design and use the repair solution 1560100270 Genuine Mercedes Benz - 1560100270 - BREATHER PIP (ecstuning.com)
This relieved the pressure dipstick popping and leaks are gone. The reason the old design is not sufficient is the small diameter of the part load pipe and the low vacuum for the full load pipe, since its at atm. pressure.
As for the newer design Post-engine 592
This design is simpler and requires the regular replacement of the PCV.
1- At idle, the high vacuum keeps the PCV shut, preventing vacuum leaks and flow.
2- At part throttle, the PCV is partially open.
3- At full load, the PCV is fully open.
Odd how they went to a limited system on the later engines (C63/M156). This means no fresh air is drawn into the crankcase to evacuate blow-by gasses, and no vacuum is applied to the crankcase, under low load conditions.
Odd choice I've never seen made by a manufacturer before.
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