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W124 m104 280E 1993
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35 Posts
Discussion Starter #1
Hello



Where it should be connected (red ring) ? To intake manifold ?

At idle it makes strange sounds - clicking, knocking... At 2000 RPM stop noising...
 

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1994 E320, 1993 300E
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364 Posts
The yellow pins connect to the wiring harness, there should be a connector floating around unter the intake manifold somewhere. The other connection is to a small vacuum line, again it is probably floating around under the intake.
 

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Mercedes-Benz 280TE 1993
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114 Posts
1993 2.8 L M104 resonance flap

Hi

I also have a 1993 2.8L M104 engine.

In mine a very short rubber hose connects the tubes in the red circle to each other.

The pins in the yellow circle are connected, as already mentioned, to a plug which must be lying somewhere in the vicinity.

I hope this helps.

Saludos,
Fernandez
 

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1994 E320
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1,729 Posts
What is a resonance flap??
Could somebody elaborate about this as it pertains to the M104 engine, please?

I do understand the general concept of variable-length intake tuning, but I'm still looking for more detailed information that pertains to the M104 in particular.
 

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12 odyssey (90k) 1995 E320 wagon (307k) 1983 500se (172k)
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3,048 Posts
Its a flap in the intake when your engine has variable intake cams.

The flap, if not working, will effectively disable the variable intake on the M104 motor.
When its not working you can definitely feel it at 3500rpm + when the variable intake should kick in.
 

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1995 E320
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2,612 Posts
That's it… intake resonance valve, it changes the "effective" length of the intake runners to increase torque at lower RPMS (being longer) and at higher RPMS (being shorter).
This. In a nutshell.

An engine has to work at various speeds and loads, and is only really efficient at one engine speed. Engineers have gone around this by changing the cam timing (variable cams) changing the lift, even the intake length. You get better torque at lower rpms with longer intake runners, so by implementing a variable system, which switches from a longer runner to a shorter runner at a pre determined switchover point, you can get the benefits of the two lengths of runners.

Same with the timing of the ignition; as the rpms advance you change the timing and gain power. Same with valve lift. And exhaust valve timing. and many other little things.
Each can be adjusted (if equipped) to lower and flatten the torque curve, boost fuel economy, increase power, even reduce harmonics and vibration. There are engines that have variable rate oil pumps too.
 

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1994 E320
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I understand all of that. That's not what I'm asking. What I want to know is how it works in the M104 in particular. Just by looking at it, I could tell that it separates/consolidates the two halves (1-2-3/4-5-6) intake plenum by closing/opening. So my questions are thus:

- What happens with the induction air when it's open and when it's closed?
- How is airflow inside the plenum affected when it's open and when it's closed?
- Under what circumstances does it open/close?
- What controls its opening/closing function? ECM signal? Intake manifold vacuum/engine load? Throttle position? All of the above?
- Humblejoe said that a non-functional flap disables variable intake. Am I to understand that if the flap/resonance valve/whatchamacallit is broken, the intake camshaft phase controller is also disabled? If so, how are performance, driveability and fuel economy affected?
 

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12 odyssey (90k) 1995 E320 wagon (307k) 1983 500se (172k)
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It effectively disables. The cam may be advanced or retarded but the length of the runners don't match what the cams are doing, so you don't get the kick in the pants @ 3500 RPM (when it kicks in).

So the engine feels lethargic compared to when its working (almost like turbo lag boost when working), and doesn't pull hard when in the upper RPMS.

Don't know wheat controls it, but it comes in @ about 3500 RPM, so it might just be RPM.
 

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1994 E320
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the kick in the pants @ 3500 RPM
I went out tonight to test the car specifically for that, and boy, that's one KITP I haven't felt in a while! the car has never felt this snappy in a while! I guess it's one of those things that just teach you to never neglect even the smallest, seemingly most trivial things.
 

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'95 E320 Wagon & '98 BMW M3
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539 Posts
I'm pretty sure the actuation of the resonance valve is strictly RPM dependent and controlled by the ECM. The vacuum line simply supplies the "muscle" to open the vacuum actuator within the valve. The actuator moves a large plate that sits down within the intake manifold. Depending on its position (open/closed), its separates the intake manifold into two halves (after the TB). So one half supplies cylinders 1-2-3 and the other 4-5-6. At lower speeds the intake manifold is separated into two halves by the valve and at higher speed, its one big manifold.
 
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