Resonator Vs Muffler instead of Test Pipes?

[NICAT]

Hi Friends.
W163 ML 2002 3.2L
My Car is loud inside. I thought it was normal but after some people complained about exhaust noise inside cabin i realised that sound level is much higher than it should be. It turned out that its cats were all replaced with universal resonator like in the photo:

I wanted to replace them with original Cats, so this way i can reduce noise level and turn off CEL light. But they are unavailable in the country for sale due to the fact that no one wants to pay high amount of money for old car and there is no strict emission control.
My Question is, would replacing universal resonators with small mufflers or with larger resonator reduce noise level ?
Thanks.

 

[mk378]

Check the whole exhaust system for leaks since they will of course increase noise. Usually a good muffler at the back is sufficient to keep noise to a reasonable level, even if the pipes from the engine to the muffler are plain straight through.

 

[NICAT]

Check the whole exhaust system for leaks since they will of course increase noise. Usually a good muffler at the back is sufficient to keep noise to a reasonable level, even if the pipes from the engine to the muffler are plain straight through.

Thanks for reply.
Do very small holes make loud noise ? For example one or two toothpick sized holes due to poor welding at difficult to reach areas?

 

[Egg_Head]

I'd check underneath and see if you have everything else that came from Stuttgart with that vehicle.

Exhaust Components for 2002 Mercedes-Benz ML 320 | Mercedes-Benz USA Parts

mbparts.mbusa.com

 

[D60]

Cats often reduce noise somewhat but that's not really the intention

If noise reduction is the goal I'd try to fit more muffler(s) or larger muffler(s)

If you want the cats or need the cats, that's one thing. If you just want to replace them to quiet it down, it's probably the most expensive route to noise reduction

As for the CEL, only you can decide if you can tolerate that -- assuming there's not a governing body making that decision for you

 

[atikovi]

Hi Friends.
W163 ML 2002 3.2L
My Car is loud inside. I thought it was normal but after some people complained about exhaust noise inside cabin i realised that sound level is much higher than it should be.

If the exhaust noise is inside the cabin, sounds like there is a leak. If not, maybe install sound deadener under the carpet.

 

[Cujet]

Thanks for reply.
Do very small holes make loud noise ? For example one or two toothpick sized holes due to poor welding at difficult to reach areas?

A pinhole is not really loud, Remember those drain holes at the bottom are typically silent. At best a small pinhole will make an air leak or clicking sound. Not a deep noise.

 

[eljefino]

It's possible whoever cobbled your exhaust together used aftermarket hangers, which transmit more noise to the floorpan than factory ones if poorly engineered.

A long resonator, sometimes 2-3 feet long, is generally regarded as having a good sound. Many cars have these from between the catalytic converter and the bend over the rear axle.

Pull up an OE parts diagram and see how closely you can match it. As others said, the cat doesn't do much for noise.

 

[NICAT]

Hi. Friends.
Unfortunately i am back after much effort
1. Replaced muffler with used one. No success (Didnt risk new one because not sure if it will help or not.)
2. I thought the noise would be emitted from Muffler itself. Bought 2mm steel sheet to add aditional layer over stock muffler with 0.6
air gap. This made muffler 8kg heavier.

3. Exhaust tip was turned down. welded 10cm longer straight pipe.
Afterward i made a test. There was no noticeable difference. 0db difference in with sound level test (Used android app which shows loudest frequency. i tested app multiple time before, the results were pretty consistent )

At Stop (D- Car wants to move but i press the brake pedal) 35Hertz RPM is the loudest one. There is no noise if the engine load is low.
During engine load noise increase. I think it is not drone because noise is at all RPM ranges. From 700 to 3000 that i tested.
Now i have difficulty finding source of since it is low frequency.

Any help is highly appreciated

 

[Cujet]

Wow, that’s quite a modification. I think adding another muffler is going to be the solution.

 

[mk378]

Is it louder *outside* than typical cars?

What is your expectation for quiet inside? The reason why older luxury cars can be purchased cheaply is that the original buyers trade them in when (for various reasons related to wear and tear) they start to get loud.

@eljefino has a point that if the rubber exhaust hangers have been replaced with solid metal, noise will be conducted from the pipe to the floor of the car and make it loud inside.

And the obvious thing of leaks still needs to be checked. If you briefly hold a rag over the tailpipe when the engine is idling, it should get very quiet and pressure should build up. If you still hear a roaring or hissing noise from toward the front of the car, there is a leak.

Every thing I see about this car is that it came with dual exhaust systems-- completely separate pipes, converters, and mufflers for each side of the V6 engine. (It may be different in other countries though). If it is dual exhaust of course you have to check both sides.

 

[thastinger]

For the CEL, since the OEM cats were removed, the ECU is not seeing the rear O2 sensors. Short of turning them off via a custom tune, there are options on the internet that act as "dummy" sensors to turn off the CEL.

 

[SubieRubyRoo]

It's possible whoever cobbled your exhaust together used aftermarket hangers, which transmit more noise to the floorpan than factory ones if poorly engineered.

A long resonator, sometimes 2-3 feet long, is generally regarded as having a good sound. Many cars have these from between the catalytic converter and the bend over the rear axle.

Pull up an OE parts diagram and see how closely you can match it. As others said, the cat doesn't do much for noise.

It’s a shame they don’t make them anymore, but for awhile back when I had my G8 GT, Dynomax made some dual-inlet, dual-outlet body muffler/resonators that had an internal X pipe, and several people found that adding this into the middle in front of the mufflers not only eliminated drone but also added some of the typical X-pipe sonic signature to the exhaust note.

Not sure if your car has dual pipes underneath, but I think SpinTech Mufflers still has some stuff that may work (or give you ideas). Best of luck!

 

[NICAT]

Is it louder *outside* than typical cars?

What is your expectation for quiet inside? The reason why older luxury cars can be purchased cheaply is that the original buyers trade them in when (for various reasons related to wear and tear) they start to get loud.

@eljefino has a point that if the rubber exhaust hangers have been replaced with solid metal, noise will be conducted from the pipe to the floor of the car and make it loud inside.

And the obvious thing of leaks still needs to be checked. If you briefly hold a rag over the tailpipe when the engine is idling, it should get very quiet and pressure should build up. If you still hear a roaring or hissing noise from toward the front of the car, there is a leak.

Every thing I see about this car is that it came with dual exhaust systems-- completely separate pipes, converters, and mufflers for each side of the V6 engine. (It may be different in other countries though). If it is dual exhaust of course you have to check both sides.

Hi.
Hangers are rubber.
At idle in Neutral, there is almost no noise. At cold start, if i put Transmission into D and press brake pedal, there is pedal shaking noise 35Hz. Too Bassy. Noise is more problem during engine load, not directly RPM related. I rarely exceed 3500 RPM, So During acceleration frequency goes from 50hz to 130hz and more
Yesterday my cousin test drove the car and confirmed the excess loud noise. He had C Class w203 2001 with exactly same 3.2L engine. Today he reported almost no exhaust noise with his car. i think this is also because mine has Hatch but his car has trunk. i think that would be effectively blocking sound.
My problem is finding the source of the noise. from Pipes or from Exhaust tip or from Muffler (adding extra 2mm gapped steel sheet cover made 0db difference )
Do minor leaks cause bassy noise ?

 

[mk378]

Have you checked for leaks at all?

Is it noisy outside the car?

 

[NICAT]

Have you checked for leaks at all?

Is it noisy outside the car?

Well.
Test 1: Transmission in Neutral at 3500-4000 RPM there is high noise outside. But inside it is pretty fine. Doors and hatches are Matted+ closed cell foam (IMHO outside noise is not more than other cars. I had other cars that made similar amount of noise at 3.5-4k RPM. Even all exhaust shops says 'this is pretty normal for 3.2L engine')
Test 2. Transmission at D, Brake pedal is pressed. Slight gas is applied, 50Hz Bassy noise inside, but at outside there is no sign of bass. Just normal engine operation. Bass is coming from front firewall area. But i think it is due to acoustic /echo of the car. Since i have noise issue at moderately high engine loads, it is difficult to inspect it at high rpms when car is parked.
I took a subwoofer, installed it just under rear seat inside the car (exact location of muffler ) and generated 70hz bass. At rear seat, close to subwoofer, there was slight amount of bass, but at front seat (especially when close to front firewall) too much bass from the subwoofer.

About Leak. Yes at the connection of glasspacks where Cats used to be, there is very small amount of leak at each side. But they did not make any noticeable noise. Exhaust shops made me believe that they are too small to cause low frequency noise. (they are at a difficult place so welders could not reach easily. some attempts were already made.)

 

[meep]

I am suspicious that this is not exhaust noise but may be vibration noise such as poor engine/transmission mounts, especially with not much noise outside the car.

 

[someonesomewhere]

I am suspicious that this is not exhaust noise but may be vibration noise such as poor engine/transmission mounts, especially with not much noise outside the car.

I was thinking the same. Especially with the noise being non-existent in park, starts being annoying in drive. Would definitely check motor and transmission mounts.

 

[NICAT]

Hi.
i want to thank everyone who posted here for help, especially those who mentioned engine mounts. .
Finally replacing engine mounts reduced volume by approximately 40% at all RPM ranges.