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Mercedes 300E 1991
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126 Posts
Discussion Starter #1
hey guys
I was wondering if any of you with a M103 3.0 engine has had your cylinder head skimmed (head gasket replaced and of course head bolts too and exhaust manifold gaskets plus intake gasket) and all valve stem seals replaced but oil still coming onto the spark plugs?
The oil is not wet when I take the spark plugs out but it looks burnt. I just replaced the plugs 100 miles ago so Im quite frustrated about this.
There has been an ever so slight hesitation at idle and Im thinking it could be this.
plugs, distibutor cap, rotor arm and leads were replaced recently. had new Bosch injectors too.
the car only has 150k miles on it. Havent driven it regularly over the last year.

Any of your relevant experiences would be really appreciated!
Sam
 

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Mercedes 300E 1991
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126 Posts
Discussion Starter #3
Hi there, thanks for trying to help..
I still haven't performed a leak down test. Would that be the best place to start, I take it?
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,745 Posts
How do you know the "black" plugs are oil? A overly rich fuel mixture will also give you "black" plugs. Has the duty cycle been checked? What type of plugs are you running? If they aren't NGK - BP6EFS or Denso T20EPU, then they are incorrect plugs...period. The ignition system requires pure copper, non-resistor plugs. Neither of these plugs is available from your neighborhood parts store and regardless of what the counter jockey may say about this, that or the other being "compatible ", they are wrong.

Jayare

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Mercedes 300E 1991
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126 Posts
Discussion Starter #5
hi again
yes the fuel mixture was set but I have a suspicion that it may be incorrectly set as I waited for the engine temp to go to operating temp and then got the duty cycle to 50%. I need to maybe read more to ensure Ive done it properly.
A possible cause for concern is that there were some bubbles in the coolant reservoir when I checked today. The head gasket and full headwork was done 20,000 miles ago. I cant imagine the headgasket failed already??
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,372 Posts
Bubbles in the coolant is a dead giveaway for either a failed headgasket or a cracked cylinder head.

I highly suspect the headgasket job was not done properly, unless the engine overheated at some point.
 

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Registered
Mercedes 300E 1991
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126 Posts
Discussion Starter #7
thanks for the input,
do u think a leakdown test will reveal a crack in the head?
I will check again tomorrow, do you think if the coolant cap is quite corroded this could bring bubbles in? but then again coolant would leak out and that isnt happening.
Should the OIL cap have any noticeable things on it ifi its the head gasket or a crack in the head? Car has never over-heated and I watch the guages all the time. All coolant related parts have been replaced in last 20,000 miles.
I must check the fuel air mixture tomorrow in case as Jayare has mentioned it may be running rich....
 

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1995 C36 AMG
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425 Posts
Could a faulty valve cover gasket be causing this? On the m104 cars there are gaskets that go around each spark plug hole for each cylinder.
 

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Registered
Mercedes 300E 1991
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126 Posts
Discussion Starter #9
I am curious about a few things so Im hoping I can get some input from those of you know what Im asking..
There is an electronic water pump bolted onto the chassis leg. Is this pump meant to be on all the time? When I put just the ignition on I can hear it making a noise. Is this normal? It looks like its got quite a bit of coolant dried on it. What exactly does this part do?

Also I checked the Rpm at Idle with a mutimeter however the figures are way off. On the Tachometer (dash reading) it read approx 600-650rpm at idle (in Park) HOWEVER the multimeter read 420 rpm!
Then I held the throttle at 1000rpm on the Tachometer but the multimeter said approx 600-650.
Is my Tachometer faulty? I have read that the Engine ECU reads the figure from the tachometer to perform its calculations. IS this correct?
Im hoping I can get some input so that I can get this car running properly. Ive spent a lot of money on this car and I want to make sure its running great!
Thank you fellas...
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,745 Posts
The pump on the frame rail is an aux water pump to increase hot water flow to the heater core when you are running at low speeds in traffic. This maintains your cabin temp in cold weather.

At this point, I wouldn't concern myself about the tach readout vs. Your meter. You have bigger fish to fry. If the reservoir cap is bad, replace it with a genuine MB or Behr cap. The valve cover cap has a replaceable rubber gasket.

Jayare


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