My experience with the M111 engine is that about every 50K miles the
Coil Packs fail.
This has been fairly consistant. However another member had told me he
hadn't had any issues with CP's with over 100K miles on them.
But unlike me, he had been using dielectric grease on the connections.

So recently when one of the CP's thats already been replaced, began to appear to fail I applied the grease.
The CEL is tripped by a mathematical formula of X number of misfires out of
X number of fires. I couldn't get it to do it again, but could feel the misfires.
If it's less, it may not trip the CEL. This can still cause issues with other parts of the car like the Catalytic Converter.

Anyway, so this time instead of just replacing it (yup, right around 50K miles on it, like clockwork) I thought, hey maybe I just need to put dielectric grease on it, since I hadn't been doing so in the past.
Amazingly the misfire went away. Today, I did the other 3 CP's putting a little of the grease on the end of a small screwdriver and putting it on the end of the plug, and also on the conductive end of the CP.

The car is running much more smoothly, whereas before I was getting a small amount of shaking.

Just an FYI- When you change your spark plugs, or replace a coil pack
be sure to use dielectric grease.

I can only assume that heat, along with humidity over time (I leave near the coast) causes some corrosion.

I'll keep everyone posted and see if this extends the life of the coil pack.

I doubt it, but do you know if the M112 engine uses the same coil pack as the M111? Also, do you have any diagrams of where exactly on the coil pack you put the dielectric grease? This sounds like something very easy to do and should be done regardless if someone is having problems or not.

Nice findings. I havent had any issues w/ the coilpacks and/or plugs. Hopefully, this maybe just be an m111 characteristic.

Old habits die hard. My little tube of anti-sleaze has lasted ~five years



Never had ignition problems. Probably just dumb luck though.

Tru - as with PS pumps - I know of 2 X 240s - one at 700,000 Km & one at 550,000 Km never had coilpacks & still running perfectly. In fairness both have run their mileage fairly quickly.

Never mind, I got a CEL on #4 again tonight.
New Coil pack on the way.

Oh wow - sorry to hear that

It's not just MBs, the wife's Audi TT 3.2 fried a coil pack a month ago. I wouldn't have minded it just mis-firing, but the bit about it catching fire and frying the connector in the middle of nowhere in the snow was a bit annoying. And if you think MB service is bad, it took Audi a week to get and replace a $20 usd connector.

wow..nice findings. Thanks for the tip...

Not soo fast. Run the next one with the Dielectric and I bet it lasts and lasts.

E

In my current issue of Underhood Service, there’s an interesting – albeit generic – article regarding coil-on-plug misfires.

www.underhoodservice.com

I've come to the conclusion that the little spring that contacts the plug becomes corroded.
Though, I had 4 fail that were either factor installed or from the dealer, but don't beleive they used the grease.
I did recently end up replacing the #4...again.
Which likely means the other 2 replaced at the same time are next.

Very interesting. I wonder whether this stacks up as a case for 2 plugs per cylinder and more frequent plug changing if you have a single plug???

The 2 plug 6 bangers aren't Coil on sparkplug...they don't get baked.

Great article.

T, I don't know if the spring is the issue. When I have gone through my CPs, I have found my springs to look like miserable little pieces of frail twisted wire. But they still work.

E

After reading through this thread to this point, I guess other people’s replies answered my own question here. So the M111 uses 1 spark plug per cylinder, while the M112 (and I also believe the M113) use two plugs per cylinder, interesting. I have just recently reached 70,000 miles on my C320 and was planning to change out the plugs. More than likely the OEM Bosch's. However, after reading this thread, I think I'm going to use the dielectric grease on the spark plug connector.

I waited for the 100K mile interval to replace my plugs. They looked great when I removed them and probably could have gone another 100K miles. Still had the proper gaping. These modern motor management systems and lead free gasoline really improve plug life.

Hmmm, if that's the case, I may just do that. In the meantime, I may take out a few random plugs from each cylinder bank to check on their condition. I'm assuming they are platinum plugs? On the newer GM vehicles, (like my 1996 Blazer, they have the 100,000 mile tune up) where at 100,000 miles, is when you actually change the plugs, wires, rotor and distributor cap.

I'm well aware of that. I think splinter was posting in the broader sense of individual coil pack per cylinder & if you understood the article - the reason for coil overheating - OTHER than ambient heat.

You just hit the nail firmly on the head. Decent Bosch plugs & no more lead errosion of electrodes = long trouble free life.

Pete, In ROW Benz recommend plug changes on the M112 every 100,000Km or 4 years. I changed mine at the 45,000 Km service under the service plan. I kept the plugs - they still look fine. My car does too many short trips & does not run in the self cleaning range for long enough. It has only just hit 50,000Km since late 2003. I had a few spluttery starts prior to changing but never any misfire codes thrown. The trouble with platinum plugs is that you can't clean them other than giving the car a good long run. Put them in a plug cleaner & they are ruined. Running shot plugs gives your coil packs a hard time as confirmed in the excellent generic article posted by splinter recently. I would just run them until you feel the car is not running quite as well as it used to or the 100,000. If it worries you observe Benz 4 year recommendation. Remember they are very conservative because they don't want the car to let you down.

I figure 60K miles between spark plug changes.
Others around here have had the opposite experience.
Waited till close to 100K mile and the plugs were toast.

Yeah 60,000 Miles = 100,000Km makes sense.

Probably on the S/C 4 bangers. I was so impressed with the condition of the plugs after 100k miles that I kept a few just to show people.

Wow, that is impressive. I once had a defective set of Bosch plats.
They were shorting through the insulator starting around 500 miles...causing misfires.
And finally it just stalled out at about 1000 miles in the pitch dark.
I opened the hood and could the arcs. Replaced plugs, and problem was gone.
Never used Bosch Plugs again.