I'm not a fan of starting threads, but I've been dealing with this grinding/grumbling problem for a while now (trying to diagnose for 2-3 months) and have looked at many avenues to diagnose it, but the problem persists. I've searched the forum for similar descriptions of the sound, but none of the solutions seems to work on mine... and I might have a different problem than them.

This is what I have had checked out so far, to no avail
-tire balancing
-alignment
-exhaust check (for rattling heat shields)
-dealer has driven my car in city and cannot notice anything wrong
-dealer has NOT driven on hwy, but i plan to recreate problem at hwy speeds my next visit

This problem can "randomly" occur during
-slower speeds, but during high rpm/tq for city driving

This problem consistently occurs when
-usually driving over 60-70mph
-ALWAYS when driving over 60-70mph AND when going uphill
-if moderate flat or decline at SAME speed, there is no noise/vibration

Description of Vibration Feeling
-mostly under my feet and from engine
-also through the exhaust
-seems to hit a resonance frequency and loud exhaust note
-minor vibration in steering wheel

Long Road Trip Evaluation (4 hours on hwy)
Driving on cruise control at 70mph on the hwy that has gradual and periodic inclines/declines resulted in periodic vibration/grinding for each incline segment. This recent 4 hour road trip in the rolling hills with consistent vibration at high speeds led to a P0302 CEL and engine shaking heavily, and loss of power while driving. The CEL went away when I stopped to fill gas, but grinding/grumbling/popping was still there.

My hypothesis
-Possibly related to the torque output at high speeds (relation to consistent occurrence when going uphill on cruise control at 70mph)
-Vibration is feeding off of exhaust/muffler (exhaust note increases with vibration)
-not related to alignment/balance (both of these have been done, however i did notice the problem AFTER putting on my CLS wheels... just doesn't make sense to be related)
-This vibration triggered the misfire P0302 code...

I'm taking the car into the dealership tomorrow. Any advice would be MUCH appreciated because I'm at a loss. I'm thinking to have them check all the mounts/joints/etc of the suspension because the engine could be hitting a resonant frequency because its not dampened properly... but thats the only guess that I have with my limited understanding of my car.

Thanks in advance!

 

100 views and no advice so far... hoping for some MBworld magic...

I will update progress regardless. these issues are difficult to diagnose, but I think I'm narrowing it down.

 

In the abscence of any other advice it sounds as if if could be from the drive shaft rear of the gearbox. Possibily worn flexible universal joint/joints or rear GB or shaft mounts.

I do not know what the P0302 Code relates to.

Interested to know what solution the dealer comes up with.

Carsy.

 

i wouldnt go to the dealership their gunna rip u off..

go to autozone and have them read the codes for free

if it is indeed a misfire replace your spark plugs and/or coil packs

 

Thanks,

The misfire seemed to happen as a result of the vibration/grumbling...

Spark plugs were replaced recently... so coil packs are a possibility, but more likely a secondary effect rather than the root cause. I appreciate the in put.

I think the P0302 is a misfire in cylinder #2.. but seems to be a result of the vibration

 

then replace coil pack number 2 its very easy to do

 

Maybe I'm not explaining properly...

I've had long-term vibration/grinding/etc... that occurs under mostly high speed conditions (especially when driving on an incline).

The misfire seems to purely a result of the vibration while driving and NOT to be the cause of it. When I restarted, it seemed to go away... however it is likely to happen again if I drive at speeds that provoke the vibration/grinding/etc...

I want to prevent the vibration/grinding/etc... from happening b/c it didn't use to before and replacing the coil pack number 2 may not do that because it could just be linked to an effect, not a cause. I'm looking for potential causes.

anyone?

 

The problem occurs under load. I would certainly replace the plug & no 2 on-plug coil.
Some of the problem could be a lazy coil. Remember that compression/bmep suppresses spark.

I would check the rear transmission mount & engine mounts. Also propshaft spline, UJ, flex discs, centre hanger bearing & rear side shafts.

EDIT - I presume the Cat is OK & not clogged.

 

i have an aftermarket CAT (kleemann) that is welded to the downpipe. From what kleemann explained in the past, it shouldn't break down.. however I'm not sure if it could be clogged. I hope this could be serviceable since it is welded on the downstream end.

I really appreciate the advice and will replace the plug and no 2 on-plug coil... however the plug is 1 month old...

Its just nice to have a list for the Stealership to go through in case they don't plan to naturally check it.

Thanks Glyn!

EDIT: what is "UJ" ? im not too familiar with shorthand notation

 

UJ = Universal Joint. There is one on the propshaft.

 

great... thanks.. i typed everything up and hopefully they won't think i'm crazy

Thanks again Glyn.

 

Hey Glyn,

My car recently had an oil leak problem where a bunch of sensors were damaged and the MAF needed cleaning, etc... because of a leak related to the cam solenoids that weren't properly fixed under the recall.

After reading about Cat failure, due to your suggestion:

http://www.all-catalytic-converters.com/techtip2.html

I am starting to believe my Cat is bad due to the following reasons:
-oil issue which probably let unburned fuel clog it up
-loss of power (my car went into limp mode while driving home today too)
-significant decrease in mpg efficiency (only getting ~21 hwy)
-misfiring (P0302)

However, I'm not sure if its related to the vibration issue. Could it be?

Until I discovered the oil leak, its possible there was accumulation into the Cat over the past few months. This coincides with the timeline that I noticed this Vibration issue.

My plan is it contact Kleemann and get a replacement Cat, but I have one question for you Glyn:

Do I need to replace anything else in the mean time? Or just first fix Cat, and see which problems (vibration noise AND misfiring).

Thanks again, you are a life savor!

I'm going to hold off from visiting the dealership and order a new Cat tomorrow. I'm just not sure if there is any other residual damage that needs fixing (apparently the replaced all my sensors and cleaned my MAF, etc.. from before).

 

If the exhaust is effectively partially blocked it can cause all kinds of crap. I might be barking up the wrong tree but it needs to be checked. I would expect the car to be reluctant to rev as back pressure builds up. You could have more than one thing wrong. You are going to have to methodically check things (as you have been doing)

 

Thanks...i feel the same, but it's nice to hear it from someone else too.

the trial and error process has been testing my patience, but i'm hopeful

 

My thoughts were cat problems, too, reading the thread - which, let me say, is one of the best "I need help" threads I've ever read. There are so many "OMG check engine light is on what to do" posts. You're very thorough and I'm sure it will be fixed up in good time.

 

Thanks!

After being on this forum for years and observing how others diagnose problems... I figured I need to make sure my future write-ups will be helpful not only for my self, but also for anyone else having similar problems. That was my goal at least...

A suggestion for moderators: There should be a template for reporting problems that includes self diagnosis, related threads, etc... If people adhere to some type of format, I think a lot of this useful information will be more accessible, making future threads more consolidated (other than repeated and circular). If that makes any sense :P

For example: If there is a button not only to start "new thread", but another that you can check/select for "problems". Then if a template could appear in your window listing causes/effects/observations/where you searched on MBworld/etc... that members could fill out. We would be more likely as a forum to make forward progress with these issues instead of repeating ourselves.

Just an idea

 

+1 I agree with LILBENZ - a well thought through original post.

John & I are working on a Wiki & I like your idea.

Us DIY'ers have a hard time compared with a dealer which requires a methodical approach. The dealer can always pull bits & pieces from the parts department to try. We can't without enormous expense.

 

Genius! Genius, I say!

 

Thanks

I would be interested in contributing more ideas to make the passing of information more efficient if you are open to them. I am very interested to see how the Wiki turns out. If you have any versions in "beta" that you want opinions on, testing, etc... please let me know.

--

Back to the related issue. I contacted Cory and Kleemann and have ordered my Downpipe/Cat... set to arrive in a week.

 

Will do. Any input & great ideas are most welcome. The task is daunting.

 

Attempted Fix: Cat replaced and added resonator
My new Kleemann Cat came in... I replaced it AND added a resonator (previously deleted).

Problems after "FIX"
I got another P0302, some crazy whining(supercharger belt?), and limp mode.

Since I just changed my plugs, my guess is that the 2nd coil might be bad. I went through and put dielectric grease on the coils/plugs... but the shop over torqued/stripped the 2nd one and I couldn't get it open... just my luck!

Drove from the muffler shop directly to the dealership in limp mode the whole way, but no codes firing. The only other time I drove it in the past 1-2 weeks, it went in limp mode then too.

I want to hold onto my car, but each of these surprises are costing me too much $$... I will have to wait and see what the dealership says. For now I'm going to search for potential causes for limp mode. Once I figure these out... I'm going to see if any of these potential causes could be related to my original cam solenoid oil leak. (any input?)

Trying to remain hopeful/positive...

 

Is it possible that your car has the dreaded early M271 head problem?

 

If you want some star time come to this https://mbworld.org/forums/events-ga...ml#post4916226

 

ahhh i hope not... any link to where i can read into this more?

thanks for the info! i dunno if i could benefit from it at this point.. but if i can figure that star could help me out, i'll definitely come by. (thanks)

 

Air intake pressure sensor is bad --> going to replace ($380 something)

and they are "100% sure" that the headers have warped at the interface of the engine block because it is leaking exhaust fumes (casing the limp mode). Either bad gasket or headers themselves. I talked to a milling shop and they need to check it out, but its a huge pain to remove them and have my car out of commission. I might just buy a new set of headers.

Could an extremely rough idle warp headers? (I'm going to try to tie this to my Cam-solenoid leak that caused horribly rough idles).