Recently failed smog.....3 times! High emissions. I think I finally figured out the problem. After replacing the EGR valve, sea foaming, and having a new cat installed (I had the original on and it was due) I still failed smog for high HC, although it went from like 1499 to about 400 with the new cat, still kind of high. So I decided to check my spark plugs and low and behold they were wet with what appears to be oil. So I decided to order new valve stems because I noticed that I have also been burning oil relatively fast. Here are my questions:

1.) Can oil leaking into the cylinder head cause high HC?

2.) Is there a way to clean the cylinder head without disassembling everything? Will sea foaming it/ fuel cleaner be enough?

3.) I am replacing my old plugs (Bosch Super H9DCO) with Champion Super (RS12YC), obviously the Champions are resistor plugs that I have and I have a set of brand New Bosch wires, will this work? I've never used any other plugs other than the non-resistor Bosch, they stopped making them so they are hard to come across, but I know I can get them from the dealership I was just curious if there would be any problem using the Champion non-resistor plugs (copper core).

4.) Changing out the valve stems seems like a pretty straightforward job, I've never done it before so are there any precautions or known calamities that a first tier is likely to make? I.e, dropping something inside the crankcase, breaking some nipple or screw, etc?


Thanks in advance guys.

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1990 190E 3.0L

The M103 is not California friendly. You shouldn't have to clean the engine after replacing the valve stem seals. Go for a long freeway drive to burn off residual oil. You have a choice of holding up the valves with compressed air or filling the combustion chamber with string. Some caution to use a flywheel lock when using compressed air. There is a special tool that makes compressing the valve springs a snap but a heavy duty version of a VW water-cooled engine valve spring compressor should work. Work on one valve at a time, keep track of the valve springs, keepers and associated hardware, use only the latest MB label valve stem seals, and note that intake valve stem seals are different from exhaust valve stem seals.

How do you know you're not getting oil past the piston rings?

Sixto
87 300D

First thing I would do is check/adjust duty cycle.

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

I don't understand.....what do you mean by getting oil past the piston rings?

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1990 190E 3.0L

Of the ways engine oil can get into the combustion chamber, the 3 common ways are seeping past the valve stem seals, leaking past a failed head gasket and blowing past worn piston rings.

Sixto
87 300D

Oh.....I didn't know about the other two, I just thought it was the valve stems because of the excessive oil consumption, the ashy gray build up on the spark plugs, and of course since the plug was wet with oil. I got a Haynes manual yesterday ('84-'88, though mine is a '90, but pretty much gives me a general idea) and thats what was noted as the problem with the symptoms I was having. There is no oil leaking outside of the engine or inside the coolant.

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1990 190E 3.0L

HC is usually ignition related -- probably the oil tarnishing it. Definitely get it done.

You need a compressor to ensure the valves don't drop into cylinder when you remove the seals.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
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2003 Gray Mercedes ML350 - 122k

If you turn the cylinder to where the pistons are all the way up, is there still the fear of the valve dropping to where the head would need to come off? If you stuffed string in as it nears tdc and then turned it to tdc for each cylinder, wouldn't the strings along with the pistons coming up keep the valves from falling much at all?

We have been there and done that...
Good spark plug pics to compare with here...
Spark Plug Horror! Look!

We did the valve stem seals and it cured this problem instantly.... smog is another issue, but definatly start with these oil seals..
tech article here...
http://www.peachparts.com/Wikka/M103ValveSeals

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2009 Mercedes ML320 Bluetec