C280 rough engine only when in gear
 

Hi hello!

this is my first post... i have a question on a rough idle in my 1998 C280... i have searched the entire forum, and found some similar posts but not exactly the same...

anyway, my engine runs rough as if the idle was too low (idle points to around 600-700) when the car is at a stand still and in gear. however, if i shift the car to park, neutral, or reverse, the engine idles normally. otherwise, whenver i am in "D" and at a stop, the car idles rough and will disappear as soon as i step on the gas, at which point the car's drivability is normal. i haven't seen any temperature-related patterns, although it always happens during the first 15 minutes of driving, and only sometimes happens after that.

can someone plz provide me with a methodical solution to pinpointing this problem? thank you!!!!

car specifics: 1998 C280, about 55k miles, always scheduled maintenance items performed per schedule by dealer

Hello

Got to wonder about the motor mounts on this one. The reason is it only does it in drive. When in reverse the engine is torqued over to the other way which would lift the motor off the bad mount. Right side mount is most likely settled and giving you the feeling it is idling rough or missing. When engine speed is increased the harmonics go away which is why you don't feel it anymore. If you have a floor jack put a block of wood on it and jack the engine up just a little bit and see if the vibration/miss goes away. WARNING! Do not jack the engine up to far or the fan can and will hit the shroud. Check that the fan is clear before starting the engine. Also use a big enough block of wood to distribute the weight of the motor without cracking the oil pan. I know it sounds crazy but it could be. I've fixed many rough/missing at idle complaints with nothing more then mounts.

Outside of that it could be a lot of things which can only really be checked out with the proper equipment like scopes and scanners and such. Good luck!

fasthair

hi fasthair!

thank you for your reply!

i tried the method you mentioned of gently lifting up the engine at the oil pan to see if the rough idle (or what i thought was a rough idle problem) went away. i think this worked!! i moved the engine up about 1/2 inch or so (can't really make a realistic guess), but at some point, the vibration that i felt through the car went away.

that was very good advice you gave... is there any final check i can do to absolutely make sure it is a bad engine mount before i go ahead to purchase a new mount?

thanks again!
pikachu

p.s.,,, you believe that it is the forward right side mount that is the culprit?

Final check? I think you found your problem. However if you want to confrim it look at the mounts left and right. I think you will find the right mounts upper metal part to be very close to the chassis compared to the left side. I would replace all the mounts if it was my car, both engine and trans mount. But yes I think it is the right mount that has settled and making the vibration.

fasthair

hi, fasthair,,,

can you help me to replace the right side engine mount? i do not know if the space around the engine compartment is as tight in the straight-6 w202's, but in my v6 w202, there doesn't seem to be any access to the engine mount from the top side of the engine.

i can see, from underneath the car, the 13mm screw that holds the bottom of the engine mount to the subframe - that's easy enough to remove. but once that screw is undone, and i lift the engine up a bit, how is the engine mount supposed to come off? there is a thin metal shield that blocks access to the top-side screws. also, the exhaust pipes seem to be too close to this shield to prevent accessing the top side screw to the engine mount.

i tried searching the forum regarding this,,, some post refer to a "engine shock" that needs to come off to get the engine mount... i'm not sure what is an "engine shock."

thank you!

I don't have the answer but thought I would help move your post back onto the 1st post page. Sometimes people don't see your post by the time it hits page 2. p.s. Welcome to the forum!

hi tank! thanks for helping me keep this post visible! ;-)

yes, i'm still looking for a way to remove to get the right side engine mount off,,, this v6 engine is just too wide,, i can't get any access to the top side of the engine mount... do you know who might be able to help me?

-pika!

Hello

Sorry for the late response to your cry for help. I sent you an email but the Mail Demon returned it. I have never replaced the mounts on the V6 in the 202 chassis. I was hoping one would come in this week so I could get an idea or some pictures on how to do this. However luck was not with me this week and none called or showed up. Maybe Steve or Gilly will see this and be able to help you. Sorry to have disappointed you but I just don't know how to do this yet. I will try to resend the email to you anyway.

fasthair

Try Stevebfl, if he listed an email. He is a master tech and very good with mb's. Good luck!

This message comes to you from the other side of the world and offers little help with your immediate problem. I hope you get it sorted, but what???!!!! a 1998 M.B. with 55 k on the clock and stuffed engine mount . From one whos looking at upgrading to a C class Im tempted to consider a BMW.!. Good Luck. I replaced an engine mount in my Porsche a year ago and thats done 167000 miles.

Hey, anybody that can help out our new member here? I've not worked on one of these either, so I can't be of any assistance. :(

I'm sure there's a way to get at it...you might need an extra-long extension, or u-joint, or flexible extension...sorry, wish I could be more help.

Mike

Hey donnie our new member needs help:)

C280 Motor Mount Replacement
 

My 1998 C280 is showing these same symptoms; vibrating in drive while stopped. It does get better once the car warms up a bit?

I asked the local MB shop for a quote to replace the mounts. They said approx $100 each for L and R mount, $30 for tran mount and $400 in labor! I asked why so much in labor, and they said its because the engine, tran and rear axle has to be aligned very carefully? Not sure what they are aligning? Are there shims or something?

I am quite good with mechanical stuff, and thought I'd try it my self. Does anyone have any advice on replacing these? It does look tight with the V6 taking up most of the compartment. Is there a good manual for this car?

Thanks for any Info.

Additionaly, only 80K miles on the car, are the new OEM mounts any better than the originals?

They're worn from age, not mileage. When the car is sitting, the engine rests on the mounts. Cars really do age with time, and often it's harder on them than mileage. The new mounts are pretty much like the old ones (my 98 C230 got new mounts this year too) and will probably last another 8-9 years...

HI Iacombe

I don't have a clue what they are talking about with the alignment issue. However once the mounts are replaced you need to readapt the "Sensor Gear Adaptation." If this isn't done chances are good you will get a Check Engine light and have misfire codes. You will need a scanner that has this function in it to re-set the adaptation.

This job has very tight working quarters and will require a few busted knuckles. My WIS shows 2.4 hours to replace both motor and transmission mounts. Good luck.

fasthair

:confused: Is it just me, or does this just not sound right??

So, 2.4 hours for all three mounts plus the "readapt"? Not bad.. :wacko:

I read somewhere that disconnecting the battery would reset the on-board computer. Would this work instead of a Sensor Gear Adaptation?

Irieite… weather is sounds right or not this is just the way it is done. I’ve been fixing MBZ for almost 25 years and go to update classes yearly. I learn something new every time and this was one of the things I learned at one of them. In fact this must be done when you replace the crank sensor, motor mounts, flywheel, ME controller and in some cases to cure misfires.

Iacombe… disconnecting the battery cables will not re-set the Sensor Gear Adaptation. It must be done with a scanner then a certain drive cycle must be done to perform adaptation. Drive the car in 3rd gear at 2,100RPM with 50% load on the motor. Now you can see why you need a scanner to do this. The only way to tell if you have 50% load is with the scanner.

fasthair

Still doesn't make sense on the motor mount swap.. Do any cables to the trans need to be removed in order to swap out the trans mount? Maybe i can see why in that case... But just for the motor mounts? :confused:

Can anyone else confirm or deny this??

At 6 years and 67k on mine, I'm probably going to have to replace the fluid filled motor mounts on my c280 as well. I did it on my 190e 2.3 and it was a piece of cake. But of course, no electronically controlled tranny there.. :D

First you must understand how the system works to detect misfires. I’ll see I can get this right. The Motor Electronics (ME) computer uses the L5 (crank) sensor for a few things one of which is telling the ME how fast the engine is running. The ME can see the slightest variation in crankshaft speed. As a cylinder fires it speeds the crank up a given amount and the engine itself moves because of this. When a weak cylinder fires the crankshaft doesn’t speed up as much and the ME flags the misfire and shuts the injector off on that cylinder to protect the cats from damage. Now with flat motor mounts the engine doesn’t rock or move as much as it will with good mounts. When the engine doesn’t move from flat mounts the crank actually spins faster because the inertia isn’t lost in the mounts flexing. With new mounts the ME will see slower crank speeds because now some of the inertia is lost as the mounts flex.

Does this make sense and clear up why the adaptation must be done?

fasthair

Well, what you said about inertia on new vs. old mounts makes sense, but if the ME can "adapt" on its own as the mounts deteriorate, why can't it do the same with new mounts? And, what about the shift adaptation issue that you mentioned earlier? I still don't get how that gets screwed up by the motor mount change.. :confused:

Yes it does adapt as the mounts settle over time. When you install new mounts this is a drastic change and the ME must be ‘told’ that this happen and to learn the new information. The ME is very sensitive to RPM change giving it the ability to detect misfire. The ME can detect a misfire that you can’t even feel.

I can make an ME system learn a motor running on 5 cylinders as running ok. Then when I make it run on 6 cylinders it will see this as bad running engine and flag a misfire code. Again this is a drastic change.

I never said anything about shift adaptation. Sensor Gear Adaptation is what I am talking about. Sensor Gear is MB speak for flywheel. Like I said earlier anytime you change one of the components I listed this is a drastic change so the ME must be told that it happen and to learn the new information.

fasthair

Thanks for the info and sorry about my misinterpretation about "gear adaptation". :o

What you've said makes sense. But, having said that, when the time comes, I'll take my chances and change the mounts myself. If it triggers the CE light, then I'll take it to the dealer or MB indy, tell them what I did and let them "readapt" it. :pimp:

C280 Rough engine only when in gear
 

First, thanks for the information on this post. I used it to test the motor mount causing vibrating engine by jacking up the engine. Sure enough, the vibrations went away. So I bought two engine mounts and one trans mount for $217 from thepartsbin.com and got to work. The book time is 2.5 hours for this job. The dealer wanted $475 parts/labor ($125 per mount). So I figured with my limited tools, working in my garage in 90 degree heat, I could get er done in 5. Disclaimer, I used to work as a mechanic for Chevrolet and Toyota. I now drive a desk as a computer analyst. Anyway, you will need Torx type sockets, E10, E12, E14 to complete the task. This is to make room to remove the huge mounts by removing the Alternator and the A/C compressor.

Don't be intimidated by the tight space, once you remove the easy to get to lower bolts on the mounts, you can jack up the engine to make room. Do one mount at a time. I did the easy trans mount in quick order. Then I tackled the drivers side mount. I figured that was the most fatigued due to engine torque. If it was a ***** and I only got one done, this would be the one to do. The top bolt is a little tighter and harder to get. I had to use a 5/8 open end wrench. It may be 16 mm, but I did not have one. It was not that tight and came out after minutes of turning the bolt by hand. Trick, you can spin the mount to lossen the bolt too. Once the bolts were out, I slipped the mount out by moving the A/C out of the way. The new mount went in and I was careful to line it up with the tabs on the frame so it angled towards the motor. When starting the bolts, make sure to start the top one firsrt since it is so tight.

I compared the old mount with the new. The old mount was 1/2 inch shorter due to fatigue. No wonder it was causing a vibration! I knew then that I had to do the other side as well.

I had it half done! Only the passenger side to go. It went about the same as the driver's side. The alternator was a ***** to line up with the brackets, I about passed out from the heat wrestling the bolts in. Once it was back on, it was smooth sailing.

Bottom line,
I got the job done in 4 hours and only lost 4 pounds. I took the car for a spin and was very pleased to find it as smooth as a baby's butt. No need to recalibrate any sensors.

Thanks guys for the help giving me the courage to tackle this job and save $250!
John Rolstead