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Old 07-06-2005, 05:05 AM
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95 C280, how do I test the coil wires

My C280 will sometimes start missing real bad and won't stop until I turn the car off for a minute or two then restart it. That usually takes care of the problem, but it seems to be happening more and more often.
In an eariler post I was told that the 3 coil wires may need to be replaced. Is there a way of testing them to make sure it's them?
I haven't changed the plugs yet, so I will attempt to do that this week but I thought I'd ask if mercedes has any kind of trouble codes that I can access. Or is that something that will have to be retrieved off a dealers computer?

Oh yea one more thing, I had disconnected the battery, in hopes that it might reset the computer and fix the ruff running problem. Now the radio dosn't work. I was told that there is acode in the owners manual for that, but nowhere in the owners manual I have says anything about the code to reset the radio. Where else might I get this code?

Thanks, Shawn

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Old 07-06-2005, 09:14 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153

You can measure resistance with an OHM meter, from the connection at the spark plug to the coil you should have between 1K-2K. Many times there is "leakage" from the wires that can be found with the coil cover removed & the engine running. Simply use a spray bottle with water * LIGHTLY spray them & see if the spark will bleed out!
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Old 07-06-2005, 11:17 AM
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Join Date: Aug 1999
Location: Florida / N.H.
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.. and even if they ohm out , change them if the spring ends are discoloered /burnt.
The problem is because they are between the coil and the plug. Benz used a spring friction contact that just does not hold up. Whereas the other three plugs have Snap connectors . They also can't get rid of engine heat as they are encapsulated.
It is common practice to change them out w/plug change as the cost is nil and they are known to cause misfires on these waste spark systems.
Bad ones also tax the ECU driver circuits and fried ones are starting to show up with regularity, so I recommend changing them just for insurance...
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Old 07-06-2005, 11:44 AM
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Location: Saugus, CA USA
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Look for the "bleeding skarks" in the dark.
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Old 07-06-2005, 10:31 PM
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Thanks for the info, from what I've been told the coil wires are more than likely my problem. What I'm a little confused about is if I had a bad coil wire wouldn't it run badly all the time? Why dose the car seem to run ok after I shut it off and restart it again?
Should I be looking in a different area or direction for what is causing the car to run so ruff at times?
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Old 07-06-2005, 10:38 PM
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Join Date: Aug 1999
Location: Florida / N.H.
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You did not ask for a diagnosis , you asked for testing info and replacement of the coil connectors.
Which I would change regardless, but my main concern with your complaint would be to see if the OVP has been upgraded to the new part# first
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Old 07-06-2005, 10:47 PM
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Is the OVP located on the passanger side of the engine compartment, back on the firewall?
And where will the part # be? will I have to remove it to get the #, or cna I see the part # without taking it out?
And what part # should I have in the car?

Sorry for all the questions, I havn't bought a service manual, or I should say the service disc for this car yet, so I'm finding everything out the hard way right now

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Old 07-06-2005, 10:48 PM
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Location: Florida / N.H.
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Archieves "OVP"

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