Motor mounts, driveline vibration and rough idle...connected? - Mercedes-Benz Forum
 
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post #1 of 3 (permalink) Old 08-11-2014, 07:06 PM Thread Starter
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Motor mounts, driveline vibration and rough idle...connected?

This is all pasted from a 10 year old peachparts post. However, with the recent realization that my motor mount R&R (done by a competent indie) was most likely the source of an intermittent driveline vibration I've chased for the past 1.5 years...I felt it needed a fresh take.

Reading this makes me wonder if the 'idle wiggle' mentioned by so many here, might be connected. If motor mounts caused driveline vibration...well, that's two of the listed reasons to have this done. I posted something similar once before about performing an adaptation test, but few chimed in. Be your own judge, I'm simply posting information I found that could suggest another step we've been missing when (DIY or indie) changing mounts.


Also, does anyone have a ballpark idea of what this procedure costs (dealer and/or indie)???

I have no issue if the experts rip into this as an unnecessary procedure, but if you do...please provide all of the supporting information to help others understand why it's not needed.

Original post:

Replacing engine mounts: W210 - PeachParts Mercedes ShopForum

"""....Can you clue me in here? What is a sensor gear adaptation?

Thanks!"""


My books say to perform a sensor gear adaptation when you change out the motor mounts on a '98 & up M112/113 engines (V6 & V8 engines). Here is the info below:

"Some vehicles have an adaptation procedure to enhance the sensitization and reduce false misfire reporting.

Sensor gear (flywheel) adaptation may be required on ME-SFI 1.0, 2.0, 2.1, and 2.8. Sensor gear adaptation started approximately in 1998 with the ML 112/113 engines. Later ME 2.8 and SIM4 may also use this function. The adaptation re-configures the ME controller for increased sensitivity for misfire detection.

Drive train influences on misfire detection are:

*Crankshaft flex
*Motor mount movement
*Torque convertor lock-up function
*Automatic transmission shift characteristics
*driveshaft and differential vibration

Misfire detection using the crankshaft position sensor requires sensor gear adaptation whenever the following componants are replaced:

*Flywheel or starting ring gear
*Crank sensor (L/5)
*ECU
*Motor mounts

In some cases, sensor gear adaptation must be performed after a misfire code.

The engine is constantly monitered for misfire to protect the catalytic convertor. The engine is analyzed by evaluating the crankshaft position sensor using a sophisticated mathematical method to determine whether precise time synchronism exists between individual combustions. Each individual combustion must prodice a characteristic acceleration at the flywheel. If misfire occurs, flywheel rotation slows slightly. These parameters are the amount of correction the ECU is making to filter out vibration and prevent setting false misfire codes. The ECU sets irregular engine running analysis or misfire detection to a less sensitive setting when driving on a poor road surface. The body acceleration sensor, or electronic vibration module, detects a rough road and sends this information to the ECU. The misfire sensitivity level can also be altered as a functional test. A lower threshold enables the ECU to detect less severe misfires indicated by reading the RPM decrease and misfire fault counter for each cylinder.

The crankshaft sensor gear adaptation mean value reflects the addition of a supplementary correction factor designed to compensate for phase error in the crankshaft sensor. This information is used to compute actual ignition timing. Each segment represents the duration between each new ignition cycle. Ignition, injection and engine speed derived from segment duration are recalculated for each segment."
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post #2 of 3 (permalink) Old 08-11-2014, 09:04 PM
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If you are saying you had driveline vibration after having the mounts replaced - if they were OE mounts Lemfoerder/Sachs you should just have the install rechecked - if the mounts were a "non-brand" then you should recheck them since it is not uncommon for China mounts to fail in one year or so..

Mounts are best diagnosed as vibration felt at idel - when in gear or reverse - which lessens substantially in neutral.

Depending on milage - the tranny mount can be checked as well.

If drive line vibration comes when going to speed, or deceleration - then flex discs are suspect.

I have not been a "sensor" resetter - most DIY'rs are not... you can reset ECU to factory defaults which gets your tranny back to aggressive factory defaults .. nothing to do with sensors
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post #3 of 3 (permalink) Old 08-11-2014, 10:40 PM Thread Starter
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Originally Posted by fabbrisd1 View Post
If you are saying you had driveline vibration after having the mounts replaced - if they were OE mounts Lemfoerder/Sachs you should just have the install rechecked - if the mounts were a "non-brand" then you should recheck them since it is not uncommon for China mounts to fail in one year or so..

Mounts are best diagnosed as vibration felt at idel - when in gear or reverse - which lessens substantially in neutral.

Depending on milage - the tranny mount can be checked as well.

If drive line vibration comes when going to speed, or deceleration - then flex discs are suspect.

I have not been a "sensor" resetter - most DIY'rs are not... you can reset ECU to factory defaults which gets your tranny back to aggressive factory defaults .. nothing to do with sensors

Hi Fab. I should have prefaced this by cross referencing the "40 mph vibration-cross post" that's also on the board. I followed that process and my long suffered pesky vibration is gone. My theory for 'why' is also detailed there.

In summary, I feel the new mounts (motor & trans..all Lemfoerder installed by a good euro shop) raised the front of the driveline a few mm. My understanding is that the driveline is "match balanced", meaning that the shaft is balanced and the angles should also match for both shafts (thus the MB alignment bulletin from the cross post). Removing the shim from my diff mount raised the rear shaft to match the rise of the front shaft caused by the new mounts. This is what fixed my vibration. If my logic is flawed, please forgive me. If you have another theory for why removing the diff shim fixed a vibration that came home 1.5 years ago with the mount replacements, please elaborate. This simple shim removal fixed a problem that almost made me regret owning the car. I think the bulletin, listed on the original UK post, lists doing a driveline alignment after motor mounts as well.

Now that the vibration is resolved, I still have the lumpy idle (which I may or may not have noticed before mounts were replaced shortly after buying the car..but I know it wasn't obvious [as it is now] or I would not have bought the car) In the peachparts post, they call it a "sensor gear" that needs adaptation?? Not familiar with sensor gears?

The fact that none of us (DIY, indie shops or MB) are doing this procedure is exactly my point. If no one is doing it, and it should be done, it could explain wide spread issues that seem minor but may not be (like so many that post about shaking at idle..as mine does). All of my mounts are new, so that's not why it wiggles at neutral/park idle..not noticed when in gear(opposite of your description above). Idle also seemed to smoothe out recently when one of my vac lines popped loose...put the vac line back on and lumpy wiggle is a good bit more prominent???

My theory:

Changing motor/trans mount changed front driveline angle, but not rear to match. This caused vibration at speed. Vibration threw off this sensor gear, causing the lumpy idle due to low level misfires. These are the symptoms they list as reasons to do the procedure (mounts/vibration) and seems logical to me in hindsight. It's likely a luck-of-the-draw scenario as well, where some motor mount replacements may have matched the diff shims and never created a vibration condition for some...while others (like me) got the opposite luck.

Blew mounts 1st few weeks owned, vibe started immediately after mounts replaced. Long list of vibration hunting:

Front bearings
Balance
Flex discs
MB Alignment
New tires (BF Goodrich)
Road force balanced
Together>Rear bearings, axle seals(old were weeping), diff dropped/checked/vent tube >>>>>>cleaned/resealed diff/fluid changed, center carrier mount checked


Also done in last 1.5 yrs
Air filters
Wires (magnacor)
Plugs
MAF/filters

Car has 75k miles now...had 64k when mounts were changed. Only remaining mechanical issue is lumpy idle.

Thanks again for you and all who contribute to this forum!!

Last edited by freedspeak; 08-12-2014 at 05:19 PM.
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