86 W124 300E sparkplugs
 

Hi,
Our 300E started to run a bit rough a week ago, so I decided to check it out. I pulled the plugs and one of the (#2) was oily and had some sort of collected debrie on it. It's solid and I am not sure what it is. I will post a picture of it later.
What could cause this to happend? It seems to have melted onto the plug itself - probably from the sparks themselves.
After changing the plug it ran a bit rougher too, as it's misfiring.

Amuso

How many miles? Yes, post a picture.

Haasman

The Pictures
 

Just wanted to let everybody know it ran smooth before I changed the plug today, which resulted in the sort of misfiring running. The earlier rough running went away after a couple of days, and was after we gased up with probably bad gas from a place that don't sell gas often.... So I suspect that the first symptoms was just bad gas.

It odometer does no longer work, but I would say close to 200.000 miles.

Here is the plug directly taken out without any cleaning...

The Pictures
 

The plug after I cleaned off some oil...

The Pictures
 

Another one...

Looks like a typical fouled plug. Assuming that the particular plug is not a "lemon" and the gap was correct, I would suggest checking the spark plug wire and hope that it's just a weak electrical connection as opposed to something wrong with that cylinder's piston rings.

You didn't say how old the plugs were or the mileage on them? Also are the wires original and how many miles on them? One thing I did notice and I have seen others running Autolite plugs in the MB's;but the owners manual does state that Bosch supers are the prefered choice.

Try to always buy your gas from a station that has a huge turnover bussiness. The gas is fresher and you are less likely to get bad fuel. Top names such as Shell Exxon Chevron etc are good choices. The times I have gotten bad fuel were cut rate bargain places. A couple of cent per gallon is not going to break you anyway.

Keith

The plugs were changed about 4 months ago. I'd say 5000 miles or so. The wires are likely the ones that came with it new.


The bad gas we got was just because we didn't have a choice at that moment on a trip. Usually always get 91 at a major dealer, or Wal-Mart here.

I will take the advice and get a new distributor cap, wires/plugs and new Bosch plugs on the next paycheck. Hopefully that will make it run good again. Good to hear that it's not likely something major. Was just puzzled that it ran rough after changing the plugs today. I guess I might have give one or more wires the final chapter fiddling around with them.

Thanks for the advice. Will post an update when I get the new wires/plugs/cap to let you know if it helped.

Wires, cap, and plugs should cure the miss. The oil on the plug is probably a leaking gasket which you should replace. If after you change your plugs, the miss comes back within a few hundred miles, pull all the plugs and recheck them. If oil is on them, replace gasket ASAP.
Good luck to you.

Valve guide(s) or valve stem seals.

Has the engine ever had valve work? Is it consuming oil?

-anthony

Amuso

It occurred to me rereading the post that you could have an engine that has worn-out valve stem seals. A good temporary measure would be to try some the "high mileage engine oils" such as Valvoline's MaxLife, or Castrol's. They have additives that swell up the valve stem seals and others. It doesn't cure these problems but does help short-term.

I have been using these oils in the '91 300E and it have reduced the oil consumption considerably.

Haasman

Thanks for the tips! Yes it does consume a little bit oil, and the valve stems has not been replaced. Oil consumption is about a quart every 3000+ miles. I forgot about the valve stems. I do believe they need replacing. The other plugs look clean and fine, by the way. I'll follow up on these tips and let you know how it goes! I'll try and replace that plug I put in yesterday with another new one and see if it helps a bit since I have another laying around.

Update on tune-up and results
 

Thanks for the input everyone! It's been most helpful.
A special thanks to Phil at the Parts Shop too. He was extremely helpful and it's always a delight to call for help. I ordered a new distributor, rotor, plugs and wire set + a new multi-rib belt as the old one was starting to show age. I figured it would be good to replace it while I was digging in there.

Disassembly took a little while, since I couldn't get the fan off, I had to swear a little at the bottom bolt holding the distributor cap in place. It helped to remove the radiator cowling (2 clips and easy come off).

Just installed the whole lot. Took me about 1.5 hr to replace fan belt, spark plugs, wire set and plugs and put all the plastic back in place.

Works like a charm! Idles so smooth it's wonderful.

The old cap was pretty badly worn out. May I guess it's been in there since the car was new? It had even cracked in the bottom where the 3rd bolt goes. Wires were pretty shabby too. Signs of cracks and someone had even used some electrical tape to try and fix one. Well, I guess it worked for a while.

Plug #2 still showed a little bit of oil. Other ones dry and clean. I am going to have the valve stems replaced soon.

Now my next project it to fix the hard hot start. I've got a new temperature sensor I am going to replace first.

Again thanks to everyone who contributed with help!

Yes, this is definitely oil fouling. Do a compression test, if compression is okay, it would be worth doing the valve seals.

Good luck,