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Discussion Starter #1 (Edited)
Intake Manifold Switchover Valve - Function, Operation, Diagnosis, Repair

Thanks to very useful info from raya, Check Codes, and senorking, along with what I learned from disassembling my intake manifold, I’m updating this OP with info I hope others may find useful.

Description:
The intake manifold switchover (or changeover) valve internally switches the intake manifold from very long runners for low end torque to shorter runners for high end power. The switchover occurs at 3700 RPM. This is accomplished by 8 metal vanes inside the manifold that divert air so it takes a longer path to the cylinders when below 3700 RPM. Above that RPM the vanes close so the air path shortens.

There are 4 vanes on each side of the manifold connected to a shaft, the 2 shafts connected by linkage to another shaft which has an external lever. The external lever is controlled by a vacuum diaphragm. Inside the manifold there is a vacuum reservoir. From the reservoir there is a vacuum line that connects to an electrical solenoid valve controlled by the engine ECU.

When the solenoid is energized its valve opens, applying vacuum to the vacuum diaphragm pot, which in turn operates the external lever causing the switchover vanes to close. Once the solenoid is de-energized, a spring inside the vacuum diaphragm forces the vanes back to their open position.

Diagnosis:
Determining if your switchover valve is actually operating is not so straight forward. If your vehicle seems to lack the power it once had under hard acceleration or when passing at highway speeds, you might consider checking the operation of your switchover valve.

(NOTE: Be extremely mindful of the moving radiator fan and serpentine belt when the engine is running!)

Testing with Star Diagnosis:
With SD you can command the switchover valve to open or close in the Actuations Menu but you can only see if the vacuum diaphragm is operating the external linkage (by peering down between the secondary air pump and vacuum diaphragm) but you can’t determine if the valve is actually operating internally as it makes no difference to the engine at idle or no load. Once you see it operates externally, shut the engine off and remove the air inlet duct from the throttle body. Also remove the secondary air pump so you can physically get to the external linkage. Open the throttle blade and insert a flashlight, screwdriver handle, etc, about 1” diameter to hold the blade open and provide light. While using a mirror to see inside the manifold, operate the external linkage manually. You should see all 8 vanes moving in unison if it’s working.

Testing without Star Diagnosis:
Without SD you will have to energize the switchover solenoid. You can do this by disconnecting the connector from the solenoid and applying 12v and ground to the solenoid terminals (polarity doesn’t matter). The solenoid uses the same connector as the fuel injectors so if you’d like to make a test harness you can salvage a connector or buy one ($6.99 at Oreilly’s). (Do yourself a favor and remove the metal retaining clip before use so the connector will just slip on and off.) You can also use 1/8” wide flat blade female push-on connectors as used for some speakers (available at Walmart), or just use clips. With the engine running or manual vacuum applied, apply power and observe for movement of the linkage as mentioned above, and as above, you will have to physically look inside the manifold while manually operating the linkage to determine if it’s actually working inside. Without SD you’ll have to connect a test light or meter to the connector and go for a drive to determine if the ECU is operating the solenoid.

Troubleshooting:
If the linkage is stuck and doesn’t move with minimal manual force to counteract the vacuum diaphragm spring, DO NOT try to force it to move or you will likely break the plastic fork the internal linkage slides in and have to replace the manifold. In this case you will have to remove the top of the intake to free up the mechanism. Note that the top seal is not available from ANY source so be gentle so it can be reused. In addition to the seal, MB sealer is also used between the top and bottom.

If not stuck, the most likely cause for failure is a rotten vacuum source line from the manifold to the solenoid. Disconnect the electrical connector from the secondary air changeover solenoid on the front of the engine to keep that solenoid from operating. With the engine running, spray carb cleaner all around the vacuum hose from the bottom of the manifold to the solenoid, especially around the bottom where it enters the manifold. Listen for changes in RPM. Any change in RPM or smoothness of running indicates there is a vacuum leak and the hose will need repair/replacement. Note that this hose is not just a simple piece of vacuum hose and it is not available from any source. It is a molded unit that connects inside the manifold and provides seal against vacuum leaking. DO NOT pull on the hose or move it unnecessarily, it will not come off/out! Repair will be discussed later.

If the hose does not appear to be leaking, disconnect it from the solenoid and put your finger over the end to determine if strong vacuum is available. If not, the manifold will need replacing or complete disassembly, or another fix discussed later.

To test the solenoid, apply vacuum (engine running, manual pump, etc.) and energize the solenoid as outlined earlier. Disconnect the hose from the solenoid to the vacuum diaphragm and place your finger over the end to check for vacuum. Replace if no vacuum.

One way to test the vacuum diaphragm and hose is to disconnect its hose from the solenoid, manually rotate the external linkage counter-clockwise to its fully engaged position, place your finger over the end of the hose to seal it off then release the external linkage. The linkage should move about half way back to its resting position then stay. Continue holding the end of the hose and watch for further movement of the linkage. After holding several seconds, remove your finger from the end of the hose and observe the linkage return the remainder of the way to its resting position. If the linkage does not hold steady part way open there is a leak in the short hose or the diaphragm itself.

Repairing the vacuum supply hose:
As mentioned, the vacuum line from the manifold is not a piece of standard hose, it’s a molded unit installed from the inside when the manifold is assembled, and it’s not a part you can purchase separately from the manifold--a pitiful design in my opinion. You can see from the attached pics that it has what looks like O-rings but are molded into it as well as being flared where it enters the manifold. What is not so apparent is a groove in it between the flare and O-rings that actually rests in the hole in the manifold.

If at all possible, salvage as much of the hose as you can. In my case the first 3 inches was in fair shape while the last 3 inches was in very poor shape, and in fact broke off while gingerly handling the hose. As you can see from the pic, I cut off all but the first 3 inches and used a 5/32” splice to join a new section of 5/32” hose. This fix is working fine.

If you can’t salvage enough to join it with a splice you can try using an elbow closer to the manifold, or use a piece of steel tubing bent into a J as senorking did in this thread: His way may be the easiest way to get something into the old hose without removing the manifold. If you can’t get a 5/32” tubing or elbow into it, try a 1/8”.

If all else fails and you don’t want to remove the intake manifold (actually not a very difficult task; I found disconnecting the injector and EGR solenoid electrical connectors the most difficult part), there is another possible solution. There is a spare vacuum port on the back of the intake next to the brake booster vacuum line. Obtain a vacuum reservoir canister, a check valve, and a 5/32” Tee from any donor vehicle (or buy new from a parts supplier). Run some 5/32” hose from the spare vacuum port to the check valve then to one side of the Tee, making sure the check valve allows air flow toward the manifold. Run hose from the other side of the Tee to the switchover solenoid, and from the remaining port of the Tee to the vacuum reservoir. The only thing left is to seal off the old hose at the manifold. Cut the old hose off close to the manifold, use some solvent on a rag to clean the area around the cut-off hose as best you can, then dob a bunch of RTV over and around the cut-off hose.
 

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The changeover happens at 3,700 rpm. Below is an extract from an MB blurb about the intakes.

Attached is also a bit more info about the change over valve. Hope this helps.

The Longest Intake Runners In The Industry
The Mercedes-Benz V6 engine features the longest intake pipes in the industry, a plus which provides outstanding low- and mid-range power. Cast into the super-lightweight magnesium intake manifold are long intake passages which spiral around to each cylinder. Incorporated into the manifold are two flaps that are closed below about 3,700 rpm, forcing intake air to take the "long route" through the manifold and build up pressure waves which boost the intake process and improve low- and mid-range torque.
At higher speeds, the two flaps open, allowing intake air to take a shortcut a more direct route to the cylinders for maximum high-speed power and efficiency. The electronic engine control unit determines precisely when the flaps are open and closed.
 

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This is a snapshot of how the switchover intakes work.



There is no way to change that hose without removing the manifold, and it's tricky even once you have the manifold off. If you have to go that route I would suggest cleaning out the passages for the secondary air injection and changing the O-rings on the injectors while you're at it.

Good luck.
 

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In case you'd like more details on that pesky vacuum line, senorking took his manifold apart (he actually replaced it) and dug into this issue, here's the permalink to the point in his thread when he focuses on the switchover vacuum connection:

http://www.benzworld.org/forums/w208-clk-class/1578871-answers-hesitation-stumble-wont-accelerate-no.html#post4653158

Further up in the thread you'll find pictures of a disassembled intake that is certainly as filthy as one could ever get. He thinks it's sand or dirt, but I suspect it's simply EGR and breather gasses accumulated over time.

Hope it helps.
 

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Discussion Starter #5
Thanks Raya and Check Codes! I got the throttle body today and put it on then did the self-adaptation but once I started it idle was very rough and fast. Last night I tried pulling the vacuum line out but wasn't able to and gave up before using too much force--I thought! I sprayed carb cleaner where it enters the manifold and idle smoothed out and got even faster--I'd torn the hose and there is a vacuum leak!!!

I'm away from home and can't find intake gaskets locally so I came up with a plan to hopefully plug it for the time being. I made an L-shaped tool to reach down and glob RTV all over and around it. It looks well covered by inspecting it with a mirror (boy am I glad I carry sooo many tools with me). I have it drying overnight after applying some heat with a hair drier to speed things up (it's so thick that after 6 hours it had only skinned over), and will apply more heat in the morning and let it sit awhile longer before giving it a try.

Being suspicious of the changeover valve after the big CLICK, I may buy a manifold. I called the yard I got the TB from and, just my luck, they sold the only manifold they had just today.:( There is another place even closer that lists one and I'll give them a call in the morn. The price they have listed is $195. I've found some for as little as $125 but shipping may equal out.
 

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Discussion Starter #6
The vacuum leak is plugged and I ran a hose from the spare vacuum port on the back of the engine next to the brake booster line and connected it to the changeover solenoid. The valve operates, at least at a fast idle when I apply power to the solenoid. Just not sure if it'll work at 3700 RPM when there is lots of air flow under load. There are four normally open vanes on each side that close off passages when the valve operates.

I found a manifold yesterday for $100 and went to pick it up, and when the igmo new-hire who pulled it off the engine came walking in with just the top I freaked. I told the clerk I couldn't use it because that seal is not available from any source. He then offered me the whole thing for $75, which I took. I then offered him $50 for the complete fuel rail and he took it. Now I have a spare set of injectors that I can send off for reconditioning without my truck being out of commission for two weeks.

The seal is actually fully intact on the upper with no residue on the lower so I think I'll just apply a little RTV to make sure everything is sealed up good. The vacuum hose for the changeover valve, though, is not in great shape, it's fairly rotten, worse than my old one. I may cover the hose with shrink tubing.

Judging from what I saw inside the manifold, and the pics from senorking in the thread Code Check referenced, and the fact there appears no way for MB to install the hose after the manifold is assembled, I believe the fitting the hose attaches to inside is part of the vane assembly (note the highlighted area in the 3rd pic). That assembly is held in by four small allen screws and connecting linkage. I didn't think about looking to see how to disconnect the linkage before bagging it all up for transport back home but once home this weekend I'll take it apart and take some pics.
 

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I updated my OP with pics and info.
Pop, thank you so much for updating your thread with all of the additional detail. It's this kind of thing that makes the forum invaluable.

My opinion about the ribs on that vacuum hose for the switchover valve is that they are there to internally seal that chamber. As we know, the intake has an opening to that chamber and if it was just a regular hose, there would be air leakage around that connection.

We're in complete agreement that it's a horrible design. I still think I'm just going to thread a regular pipe fitting into that opening, so it will be permanently sealed and still have vacuum to supply the switchover. It's not a perfect solution as there is no expansion chamber to reserve vacuum for those rare-ish occasions when there isn't sufficient vacuum otherwise, but following the 80/20 rule, I think it will be fine.

Take care and enjoy the ride,
Greg
 

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Discussion Starter #9
Greg,

That ribbed area certainly does provide vacuum seal. It is held against the bottom of the manifold (i.e. sandwiched) by the attachment point. I purposely pasted two pics of the inside together to help demonstrate that. Of course either the top or bottom has to be rotated 180 deg so the two pieces can mate.

I'm afraid the switchover won't work properly without a reservoir and check valve. Remember that the switchover occurs at 3700 RPM. This is normally a very low vacuum condition because the throttle blade is open pretty wide if not wide open, and there's a pretty good spring inside the vacuum diaphragm. I suppose some testing could be done to see if it will work, either by connecting the solenoid to the spare vacuum port next to the brake booster port or by logging vacuum readings above 3700 RPM and then using a hand vacuum pump with a gauge to see if the diaphragm will open and stay open with that amount of vacuum; however, air flow acting against the vanes could also play a part in how much force is required for the switchover.

Perhaps stacking several o-rings on the end of the hose such as I've pictured below would work. It seems that would perform the same function as the original. Because 5/32" hose is a little bigger than the hole in the manifold, you'd have to taper cut the outer end as pictured so it can be started through the hole from the inside then grabbed with some pliers to stretch/pull it through a ways before stretching/pulling the remainder through by hand then cut the hose to length squarely.
 

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Technically it's only needed for a short period. When you first open the throttle, vacuum falls flat, but as the rpm climbs, vacuum comes back. At least until the engine is under a heavier load. That's what the reserve chamber does, it supplies vacuum until the revs catch up.

I have no doubt that outright performance may suffer, but I don't drive hard, so I don't think I'll notice it. If I do, though, I can always install one inline as you did with the back port. Either way, I won't have to worry about that port ever presenting a problem again. ;)
 

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Discussion Starter #11 (Edited)
Technically it's only needed for a short period. When you first open the throttle, vacuum falls flat, but as the rpm climbs, vacuum comes back. At least until the engine is under a heavier load. That's what the reserve chamber does, it supplies vacuum until the revs catch up.

I have no doubt that outright performance may suffer, but I don't drive hard, so I don't think I'll notice it. If I do, though, I can always install one inline as you did with the back port. Either way, I won't have to worry about that port ever presenting a problem again. ;)
For testing, I installed a microswitch (see pic) that activates when the intake switchover valve operates and connected its normally open contacts in parallel with the brake fluid reservoir level switch. This provides both visual and audible indication whenever the switchover valve operates.

The first thing I noticed is the valve does not operate at 3700 RPM, or any specific RPM. It appears to be load dependent rather than RPM. I've seen it switch as early as 2200 RPM and switch back below 3500, and seen it not operate at wide open throttle all the way to 5500 RPM. It doesn't stay switched over for long, usually 1 to 2 seconds, the longest I saw was maybe 4 seconds. It seems to operate more when accelerating from around 25 to 45 than when flooring it from a stop or flooring it from highway speed.

When connected straight to vacuum without a reservoir, I could not get it to operate at all. I picked up a check valve today but still need to locate a reservoir to test it that way. Hoping I can do that this weekend. I have to take a 150 mile trip tomorrow then return the following day and will do further testing along the way and update my OP with results.

From what I've seen so far, the valve operates so little that I'm not convinced it provides enough benefit to warrant trying to repair, it would be just as well plugged off but I'm reserving final judgement pending more testing.

Edit: The short duration of operation could be that my check valve is not working properly; it's something I need to test.
 

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Discussion Starter #12
The short duration of operation could be that my check valve is not working properly; it's something I need to test.
The check valve was the issue with the short duration of operation. I found a reservoir and connected it along with a check valve and the switchover valve now stays open longer.

Load is definitely the primary criteria for controlling the switchover. RPM and either speed or trans gear (not sure which yet) also play a role. At slower speeds, under 25, the switchover occurs at 70% load when above 2000 RPM. At higher speeds, the switchover occurs at 75% load when above 2200 RPM. Once load gets below the 75% (or 70% at slower speeds), it switches back.

The switchover valve works the same when connected to the spare vacuum port on the rear of the manifold as it does when connected to the normal port as long as you have an external check valve and reservoir.
 

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In despite of my attachment to W210, I have similar M112 engine like W163 have, so I have my experience with disputed question about discussed intake changeover valve of intake manifold
So, for correct work of vanes, vacuum reservoir is to be unbroken!
I mean that main problem is in rubber valve inside manifold. And this valve is unchanging! There is no adequate way to repair vacuum reservoir and this rubber valve. But my friend (his words) repaired by replacement rubber valve by screw and nut! screw and nut in accordance with vacuum begin work like a valve. No another way!
I had no torque at 1000-3000 rpm about 3 years from date of purchase of my car. I have experienced 99% manipulation but repairing this rubber valve and change of rubber splice!
I decided to change intake manifold to used and... result exceeded expectations.
So, do not suffer, change manifold to used with alive (I mean working) rubber valve inside manifold. No any manipulations
sorry for my English)))
 

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Discussion Starter #14 (Edited)
Kruger,

I just replaced my intake manifold but did not have a vacuum pump handy when I did to test the check valve. Unfortunately it did not work properly. My old manifold may have a working check valve but I'm not sure it's worth changing the innards. First, it works fine with the external check valve and reservoir I hooked up, and secondly, the switchover occurs so infrequently and for such a short duration in the course of driving that I'm not sure it's worth having. In the past two days I drove 400 miles hauling 1/2 ton of passengers and cargo while purposely driving with a heavy foot so the switchover would come into play as much as possible (5 to 10 MPH over the speed limit and jackrabbit take-offs, 325 miles of that hilly highway, 75 miles city) and out of those 400 miles I'd be surprised if the switchover was active for two miles total. That's a mere 1/2 percent duty cycle--when trying to make it work.
 

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Hi, guys
in continuation I mesured vacuum in intake manifold by Vacuum Gauge
I connected hose of gauge via an plastic adapter to hose of solenoid.
what I noticed... I noticed that vacuum at vacuum reservoir (hose of solenoid) is 20 kPa!
And vacuum at intake manifold (I connected gauge and tested vacuum near throttle) was 30-40 kPa,
and vacuum near throttle reacted to the acceleration in contrast of vacuum reservoir inside of
intake manifold. Vacuum inside reservoir was stable about 20 kPa.
So... I can conclude that there is no problem to diagnose vacuum reservoir.
Only necessary to connect gauge and overwatch for work of vacuum reservoir at idle and even
moving by watching to gauge throgh windshield.
 

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The first thing I noticed is the valve does not operate at 3700 RPM, or any specific RPM. It appears to be load dependent rather than RPM. I've seen it switch as early as 2200 RPM and switch back below 3500, and seen it not operate at wide open throttle all the way to 5500 RPM. It doesn't stay switched over for long, usually 1 to 2 seconds, the longest I saw was maybe 4 seconds. It seems to operate more when accelerating from around 25 to 45 than when flooring it from a stop or flooring it from highway speed.
I noticed same processes as you described. I noticed it when assembled vacuum gauge to pipe after solenoid! I watched a gauge driving car!
So, simple way to test work of switchover is connecting a vacuum gauge and watching it by driving your car.
 

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The changeover happens at 3,700 rpm. Below is an extract from an MB blurb about the intakes.

Attached is also a bit more info about the change over valve. Hope this helps.

The Longest Intake Runners In The Industry
The Mercedes-Benz V6 engine features the longest intake pipes in the industry, a plus which provides outstanding low- and mid-range power. Cast into the super-lightweight magnesium intake manifold are long intake passages which spiral around to each cylinder. Incorporated into the manifold are two flaps that are closed below about 3,700 rpm, forcing intake air to take the "long route" through the manifold and build up pressure waves which boost the intake process and improve low- and mid-range torque.
At higher speeds, the two flaps open, allowing intake air to take a shortcut a more direct route to the cylinders for maximum high-speed power and efficiency. The electronic engine control unit determines precisely when the flaps are open and closed.
Hi, please can you help?
I've recently bought my first 2006 C180 Kompressor and have been doing some reading.
I disconnected the EGR system and blocked off the hole in the SC inlet pipe. I saw that the 2 vacuum pipes lead under the engine cover to a changeover valve.
The changeover valve is still connected, but not receiving vacuum from the EGR system. I've noticed an increase in low end torque and a drastic decrease in fuel consumption.
Please can you explain why a change over valve is needed and if unplugged, would it damage the engine?
 

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Hi, please can you help?
I've recently bought my first 2006 C180 Kompressor and have been doing some reading.
I disconnected the EGR system and blocked off the hole in the SC inlet pipe. I saw that the 2 vacuum pipes lead under the engine cover to a changeover valve.
The changeover valve is still connected, but not receiving vacuum from the EGR system. I've noticed an increase in low end torque and a drastic decrease in fuel consumption.
Please can you explain why a change over valve is needed and if unplugged, would it damage the engine?

You are on the wrong forum.

W203 C-Class - Mercedes-Benz Forum
 

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Hello .
I have the following problem with my intake switchoff valve system on m112 3.2.
It doesn`t work .

I have:

1. Changed the solenoid - no changewhatsoever .
2. Checked the vacuum from intake manifold to solenoid - there is vacuum , which is good .
3. Checked the voltage on the cable , which controls the solenoid - 10.5 volts which are constant ( no matter how you rev the car ) . I suppose this is not good , right ?
4. The diaphragm and link to the flaps are working fine - tested them with external vacuum , they are working okay .

Is there a way to test this solenoid with STAR diagnosis . If yes - which menu exactly ?
There should be 12 volts to activate the solenoid , right ?
 
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