Vacuum leak help.
03-01-2011, 05:55 PM
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'08 CLS63
Vacuum leak help.
I have a cls 63 and at idle it squeals badly. I’ve eliminated the fan, belt or tensioner. It’s a vacuum leak from the back of the motor. Anything above 1k rpm, the noise goes away. If I pull out the oil dipstick at idle the noise goes away….leads me to believe it’s a vacuum leak…and it’s coming from the back of the engine. When turning off the car, there’s a whoosh noise coming from the back of the engine that sounds like it’s relieving pressure. I assume the problem has something to do with crankcase ventilation. If I put my finger over the dipstick opening, the engine revs up.
Any ideas what it could be and/or a fix. I know the c63 guys are gear heads when it comes to the M156 and thought someone might have an idea? The car is still under warranty but my dealership is 50 minutes away…rather fix it myself if it’s easy. Thanks for your help in advance, John
Any ideas what it could be and/or a fix. I know the c63 guys are gear heads when it comes to the M156 and thought someone might have an idea? The car is still under warranty but my dealership is 50 minutes away…rather fix it myself if it’s easy. Thanks for your help in advance, John
03-01-2011, 08:11 PM
#2
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2012 C63;1971 280SE 3.5(Sold);2023 EQS 450 SUV 4 Matic (Wife's)
I am not sure on the M156 but in general the crankcase ventilation should work like this. Have you had the intake off at any point or replaced it by an aftermarket CF intake?
There should be a vacuum type line after the MAFs (so maybe two lines) and before the throttle bodies that supplies metered air to the crankcase. Check to be sure these are securely fastened and in good condition at the rear of the intake. There will be a vacuum line from the valve cover(s) to the intake manifold after the throttle bodies that draws air from the crankcase under vacuum from the intake manifold. Again check to be sure these line(s) are in good shape and securely fastened. There may also be a PCV valve in the valve cover that needs to be checked. It is a one way valve to allow air out of the crankcase but not back into the crankcase. That is the PCV system in general and I am not sure how it is run on the M156 so you might have to dig in and see what you can find.
I suppose it could also be a vacuum line to the brake booster. It will come off the intake manifold as well and supply vacuum to the booster so you can follow that from the booster to the engine and check that out as well.
GL
There should be a vacuum type line after the MAFs (so maybe two lines) and before the throttle bodies that supplies metered air to the crankcase. Check to be sure these are securely fastened and in good condition at the rear of the intake. There will be a vacuum line from the valve cover(s) to the intake manifold after the throttle bodies that draws air from the crankcase under vacuum from the intake manifold. Again check to be sure these line(s) are in good shape and securely fastened. There may also be a PCV valve in the valve cover that needs to be checked. It is a one way valve to allow air out of the crankcase but not back into the crankcase. That is the PCV system in general and I am not sure how it is run on the M156 so you might have to dig in and see what you can find.
I suppose it could also be a vacuum line to the brake booster. It will come off the intake manifold as well and supply vacuum to the booster so you can follow that from the booster to the engine and check that out as well.
GL
03-10-2023, 12:17 AM
#3
Bump, I have exactly this issue but cannot find any leak. New pcv.
