Nicholi2007

2002 Mercedes C240
Current Mileage: Approximately 78,000
Plugs changed at 52,000 miles to Bosch Plat 4.

Symptoms:

I started to experience some vibration a few months back and assumed it was the engine mounts since no CEL came on. It feels like its coming from under the seat at times and its rather violent with the thought of "this could be trouble" running through my mind. It feels like something is about to fall off.

Action Taken:

I went to an independent shop here in Los Angeles. The mechanic swapped out the engine mounts only to discover that the shaking became more severe from a cold engine. The old engine mounts were less than 50% so I decided to leave the new ones in.

Assessment:

The mechanic hooked up a computer and determined that the problem was coming from cylinder no. 5. He suggested I swap out the cables.

I ordered two new cables (G, both short) and will install them to see if this remedies the issue. It could be the coil pack.

I'll update as I move through the process of elimination. I welcome any comments.

Glyn M Ruck

That's interesting. It's often Cyl 5 that goes first. I suggest that you get hold of a scanner & move the coil & leads for cyl 5 to another location. If the misfire changes to the new location you know whether it coil and cables causing the problem. Mark the coils with a felt pen so you don't mix them up. Misfire codes = 301 to 306 in your case or 300 = multiple misfires.

It could be other things but do this first & let us know.

Nicholi2007

I hooked up the Cen-Tech OBD II scanner and no codes. The misfire monitor says OK. I did not expect anything since there is no CEL. The mechanic is claiming that its a slight misfire which is why there is no CEL. For a slight misfire, the vibration seems strong.

Once I get the cables, I will put them on. I am starting to suspect the coil pack. I am also wondering if an O2 sensor could cause this.

Glyn M Ruck

O2 sensors tend to cause the engine to stumble under acceleration & should give you a fuel trim code. I'm surprised there are no stored codes. You can have stored misfire codes without the CEL coming on. It has to have enough misfires to trigger the CEL.

Change the leads - Why did the mechanic suggest Cyl 5? - it must have shown codes which he deleted - & maybe change the coil pack.

Before you spend any more money - please check the MAF - just to eliminate it from the equation. Unplug it and let the car run on a default map. If this makes no difference then replug it and cancel the code it will throw.

Does anything rattle in the exhaust system?

Nicholi2007

Exhaust System Rattle - None

I started the car up and waited until it warmed up. I listened to the exhaust from the driver’s side and looked under. I did not hear any rattling or see any strong vibration.

Cylinder Misfire on No. 5

The mechanic hooked it up to the computer and informed me that the misfire was originating from cylinder no. 5.

I reviewed the spark plugs DIY and realize that I made two mistakes.

1. I did use any ant-seize but FORGOT the dielectric grease.
2. I did not use a torque wrench as the final step. I just tightened them so that they were real snug. I did not want to over tighten and risk a problem later.

On Monday, I will call the mechanic and ask for more info and see if he cleared any codes. The new cables should be here by wednesday at the latest.

I probably should buy and apply the dielectric grease to the tips. I guess a clean rag should suffice to clean?

Plugs can be defective; I'd rather buy a new plug first and replace it before buying a new coil pack.

Glyn, Thanks for all your help.

Glyn M Ruck

Good - then you likely don't have a piece of catalyst broken off.

Yes, plugs are worth another try even with 2 per cylinder. Dielectric grease is a good idea. Lack of it is not likely the cause of misfires but coil packs seem to last longer with it.

Nicholi2007

Just came across this from NGK's Website:

Torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind.

Off to get a torque wrench!

Glyn M Ruck

Yes, plugs must be tightened just right for proper heat transfer - not too tight either. Detonation is unlikely in a modern vehicle but it's still important to get this right.

splinter

In response to your PM, their torque specification ~22 ft-lbs/30 Nm.

https://mbworld.org/forums/c-class-w...-plug-r-r.html

Nicholi2007

I finally received the new Bosch cables and it seems near perfect but I still feel a slight vibration. I wonder if the coil pack may be damaged.

Their is some bad news.

1. I dropped set of foldable allen wrench tools that I used to tighten the coil screw. It landed at the bottom of the engine. I guess its sitting on the tray. I suppose I could drive around and see if shakes loose and falls out.

2. It sounds like a guide is loose. I hear a high pitch wheel sound almost like a "space ship" sound. I have a recording taken with the iPhone and the quality is descent but can't upload.

3. If I turn left sharp such as turning into a drive way to turn around, I hear a crunch noise. I wonder if a bushing is going. The odometer has 78,000.

Glyn M Ruck

Allen keys are as hard as hell - get them out of there before they get caught where you don't want them & do damage - If you can't fish them out with a piece of wire the drop the cover plate.

You are going to have to give us more detail about "space ship" noises.

Check your Castor bushes



https://mbworld.org/forums/attachmen...h-bulletin.pdf

Also check sway bar bushes & links

Ignore VIN numbers - applies to all W203

Nicholi2007

Took the cover plate off and it was sitting on the edge of where the next cover plate connects. The "space ship" noise is a high pitch that appears in the background when the engine is running. It sounds like a wheel is loose or does not have enough grease. It vacillates in sound pitch. Art times it is more easily heard and at other moments you have to listen for it. Its seems fairly consistent. My instinct tells me a belt guide is loose or on its way out.

I'll check out the remaining issues per your sage advice. An impressive display of knowledge; many thanks Glyn!

Glyn M Ruck

Space ship noises. These engines do produce some high frequency noise that seems temperature dependent. Don't be too concerned. The things that fail are usually the belt tensioner/pulley or the idler pulley.

Nicholi2007

The mechanic says he does not clear codes unless he fixes something. I did a rescan after connecting the new cables and MIL status says OFF, no codes. The car is due for a smog check so hopefully everything is A-ok.

Nicholi2007

I'm still getting a vibration under the driver's seat BUT only when the car is in Park and idling. In Drive with my foot on the brake, nothing.

Anyone have any thoughts?

Glyn M Ruck

Check the rear gearbox mounting

Nicholi2007

Had it checked out and they say its fine. I ordered a new coil pack to replace for cylinder 5. I'm going to install shortly to see if that solves it.

New problem

On the left side of engine (passenger side) I saw that the spark plug cable was soiled (middle coil pack). Put my finger under it and there was fresh oil, not good.

Also noticing a fair amount of black dirt and oil around the whole engine.

I wonder if the gasket seal is going and/or perhaps the spark plug seal.

Going to take in to the shop on Monday.

Glyn M Ruck

See TruTaing's thread on cam cover gaskets & sealing the crankcase ventilation covers on the camboxes.

https://mbworld.org/forums/c-class-w...03-thread.html

Nicholi2007

Glyn,

I searched and found his thread. Many thanks. I also found a source for a step by step process for replacing the Valve cover gasket with pics. I posted a link on Trutaing's thread:

https://mbworld.org/forums/c-class-w...ing-cover.html

Update on Misfire & Shaking Issue:

The mechanic replaced the engine mounts mistakenly at first and then realized it was a misfire. The engine mounts were low so I decided to leave the new ones in. I replaced the coil and leads on cylinder 5.

I took the car in today. He hooked it up and said A-ok, no misfires. He stated that he needed the car "cold" in order to determine where the vibration is coming from and thought it was very minor. He did ask if it was involved in accident stating that something could be coming into contact and thus the vibration. It did not feel like this at 48,000 when I bought the car and no accidents since I have owned it. It now has just under 80,000. Maybe its time I went to the dealer.

Glyn M Ruck

One thing I would do is replace all plug wires. You are at about the mileage that they can play up.

krisv420

Bing... Search for my thread on doing this on my c320... I had the same issue as you

Nicholi2007

Kris, I did thanks. Glyn, I concur with your assessment and will procure a replacement wire set. I wonder if all the coil packs should be replaced as well. I'll take it one step at a time.

I really appreciate everyone's input.

samaritrey

i would do what others here do and have an extra coil pack in the car for emergencys. on the m112 the coil packs seem to last way longer then on the inline 4's. on the m112 they don't get as hot which seems to help them live longer. i have not replaced any of them on my car in the 49,000 miles i have owned it. btw my car has 135,000 on it.

Nicholi2007

I replaced the wire set with Magecor. They were much easier to put on. A few days ago, the vibration started to become more pronounced so that's why I installed the new set. The vibration is almost gone so it might be the coil pack opposite cylinder No. 5 since I found oil on the cable. I am going to swap it with the used coil pack left over and see what happens. I probably should bite the bullet and replace all the coil packs.

Going to switch to Denso plugs as I am questioning Bosch PLATINUM IR FUSION.

Glyn M Ruck

I only use OE Bosch plugs - You could have a coil problem. If changing the plug wires made a noticeable difference to smooth running then I'm sure your problem is ignition system related.