hauserc

We have a 2008 CL600 that we have had since new. It has about 80000 miles on it. Recently, it has started making a very loud bang when started in the morning. It happens about 2-3 seconds after starting. The car is in park. The car has to sit overnight for this to happen. Once it happens, it will not happen again unless the car sits overnight. Sounds like it is coming from the engine compartment. It is very difficult to figure the exact spot because it only happens once-a-day. Once it is started and the bang happens, if you turn the car off and then restart, there is no bang. It is loud enough to feel it in the brake pedal and steering wheel. It has now been at the Mercedes dealer for over 2 weeks. The difficulty they are having is that they only get one shot a day at it as the bang wont happen once its happened already. The mechanic then needs to wait till the next day to try it again to see what's wrong. They replaced a strut that they thought may be doing this. I didn't think it was a strut based on the thunderous bang the car makes but they tried it anyways. Sure enough, we picked the car up and it banged the very next day. Any thoughts on what could be doing this? Backfire??? fuel problem??? Any help would be great.

ItalianJoe1

I've heard of that happening on ABC cars with collapsed accumulators. Have you ever replaced them? at this age/mileage, they are worn out and due for replacement.

Welcome to the forum BTW.

hauserc

They have not been replaced. If the accumulators were bad, wouldn't the suspension be sagging or low. The car seems to maintain the proper height overnight. The cause has to be something that takes a long time to buildup as the car has to be absolutely cold and sitting basically overnight. It happens about 75% of the time the car is started in the morning.

ItalianJoe1

Nope, the accumulators only store pressure when the pump is running (why you hear a pop after startup, it takes a second to pressurize the system), and are only responsible to provide backup pressure for system spikes when driving. They are like a balloon in theory, they won't leak externally, they just won't prevent pressure losses when they are supposed to.

ItalianJoe1

Fair warning, most people, even MB dealer techs, don't understand the ABC system. The fact they replaced a strut is a good indication of that. One has nothing to do with another.

hauserc

Thanks for the info. The dealer is changing the accumulator(s) to see if that is the issue. They contacted Mercedes technical support and they advised to change them to see if that fixes the issue. Seems to make sense. If it's not the accumulators , it's back to square one .

rxzoco

any updates did you fix it? after the accumulators

07CL550Benz

I'm also curious to know, experiencing the same thing.