Plug Erosion from Electronic Ignition? - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 11-28-2009, 03:35 AM Thread Starter
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Plug Erosion from Electronic Ignition?

Roughly a year ago, I drove my '73 280se 4.5 from San Diego to Denver (about an 1100 mile trip). Prior to, I had changed the plugs, wires, etc. My dad's got the car currently, and has put another 100 miles or so on it. It began to misfire so when he checked the plugs, he found that they were badly eroded and also fouled.

I've got a Pertronix unit with a high energy coil in the car, and am wondering if anyone has had a similar experience. He read somewhere that the gap should be 20 thousandths (not that I remember the normal, rated gap for the original setup), and when he adjusted it as such, the car ran like a champ.

Any thoughts on the matter?
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post #2 of 2 (permalink) Old 12-05-2009, 04:46 AM
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I'm not familiar with the Pertronix set-up. I guess I should say, I don't use the Pertronix but I do use the Crane optical set-up with a high performance coil and I have never noticed any problems.

What type of "erosion" are you talking about? A white, glazing or melting of the porcelain? That is usually the sign of either a lean "burn" or a too advanced spark ignition. Could be a vacuum leak or you have the mixture set too lean.

Melting of the electrode or center contact? Definitely an "over voltage" condition.

Try changing to a "colder" plug if everything else checks out.

Plug gap's original specs are .028"or maybe it was .023". I run my NGK BP6ES's at .032" to actually promote a hotter spark, 'course that is on my M110's and M115.

The original "close" gap was because the stock Benz ignition is weak and the voltage was reduced through the trigger switch points to enhance longevity hence the "transistorized" spark booster box.
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