88 300E 270K Km

One of my lovely 300Es has developed a new headache. It started a month ago when I noticed a miss and the number 6 plug kept fouling. Wet, black carbon buildup when cleaned off, the motor would return to that nice purr we all love to hear. It has gotten progressively worse but/and it is still intermittent. I've swapped distributor cap and wires, new plugs etc and at this point I'm thinking ring, lifter or valve guide. Very on and off, I get some serious blue smoke which might occur for 3 or four minutes and desist.

Clean the plug again and until this week I'd get a couple of weeks smooth sailing. Now I'm cleaning every other day. There is no valve noise of any kind and I've not been able to do a compression test yet. I ran some Lucas additive when this first started about 2 months back and it cleared up briefly. If it is a lifter would there not be noise associated with? I'd hate to find out this was a broken ring but doubt it would be since the problem comes and goes. Are any of those additives any good?

This is the 300E I was having problems with the OVP and FPR which really isn't completely resolved but I've cleaned and checked all the sensors and idle sensors and the idle isn't as bad as it was. Only thing left to check is the O2 sensor in the next day or two.

This miss is unrelated however IMO, it's only that one cylinder, so I'm wondering what suggestions anyone might have. I plan to sell this car asap since I've got the other running well but I'd like to at least have a better sounding engine than it currently is to get a half decent price.


tia

Blue smoke = burning oil. Which means oil is getting into the combustion chamber, which is why you are fouling that #6 plug.

To see if it's the rings do a compression check. If #6 is not lower than the other cylinders, it's just the valve stem seals. If it's got low compression, it's the rings. But it would be odd to just have one cylinder with bad rings. Valve stem seals are known to wear on the top end of these motors. I did mine at 122K when I did the head gasket replacement, just to be safe.

Additives really won't do much to help your cause and are generally a waste of $$. Either fix the problem by doing the diagnosis above, or sell the car as stated. Good luck!!

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1991 300E - 212K and rising fast...

What a kick that would be. Doing that kind of work (heads or rings) would approach the price I'd get for the whole car. Wrong time for this to happen.

The seals? Big job? Means pulling the head, gasket re and re and all the rest. I think I'm answering my own question already.

Oh well...thanks for the advice. I'll run a compression test next.

Well, if you sell the car with the problem disclosed, AS-IS. You should still be able to get OK money for it. One cylinder that burns a little oil may not be a huge issue to someone. Or some people would probably just do the job themselves and save the $$$ of taking it to a mechanic.

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1991 300E - 212K and rising fast...

Forgot to mention. Doing the valve stem seals is a not a bad DIY. If you can get a valve spring compressor. Don't need to remove the head.

http://www.peachparts.com/Wikka/M103ValveSeals

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1991 300E - 212K and rising fast...

Most of the chain stores have valve spring compressors for loan too.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

This really has me stumped. Anytime I get the "smoke" it only lasts for about 3 or four minutes and clears up. Maybe twice in a one hour drive on city roads below 60km.hr. Never happens at highway speeds. It can't be rings or it would be continuous. (I've had cars with broken rings and know what to look for) There seems to be a part of the cycle when I come to a full stop for instance waiting for a light to change. A steady blue smoke stream will billow out of the exhaust and go away within minutes. The misfire has me stymied. Today and yesterday it was constant, after plug cleaning even. I went for a 30km run today on the highway and it was with me all the way in one direction. On my return it cleared up completely without so much as cleaning the plug. Since none of this is constant and I don't have much experience with the Benz motor I can't pinpoint what's happening.

Main questions here is, if a plug is misfiring, could oil accumulate in that cylinder or are they independent? A bad lifter would be noisy - there is no valve noise whatsoever. No piston or bearing noise. When plug #6 is removed it smells gassy and has a black buildup of baked on wet carbon.

Lastly, the duty cycle shows me running very rich overall and the other thread we're in about having problems with my FPR snd OVP with low idle.
I posted a followup just now to that thread as well.

You are correct. Bleu smoke due to broken/worn rings is a consistent problem, not an intermittent one. Which points to the valve stem seals! Typically on decceleration is where valve stem seals leak, so it would make sense that just cruising on the highway wouldn't produce the symptoms. Wheras city driving is a constant up and down on the RPMs......

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

Thanks John and TnBob - I may just proceed with this since I've done some heads on domestics before and they can't be all that different. Selling the car is still up in the air, I may just decide to park and keep it, or do the head and tack the cost/labor onto the selling price. A new head gasket sure wouldn't hurt along with seals. Until then I'd like to figure the rest of this out. Since the smoke isn't steady there's more to this I'm thinking/wondering.