w108,107 Parts Hoarder
Date registered: Jun 2010
Vehicle: slc5.0cab 280sl5sp 280se4.5 500sl92 GONE:280sl79 4xW114/5 3x450sl72-3 280slc4sp81 280s69 73,81SLCs
Location: Philadelphia Area
Mentioned: 27 Post(s)
Quoted: 1573 Post(s)
Fouling sooty plugs are from a rich situation, and in my experience, the "rich" comes from spark plugs not sparking when they should, or as strong as they should. Then the fouled plugs make the spark even weaker.
I think you have already found that you have a spark issue, and thers no need to go messing with the fuel issue unless you happen to think that injectors 4 and 8 are staying open too long. Has anyone had that happen she the trigger points get dirty or bent? I thought the failure mode on a d-jet was no fuel. If I'm correct about that, all the trigger point and injector / ECU talk is barking up the wrong tree.
Cylinders 4 and 8 happen to be the longest spark if wires and often the hardest to reach. I have found that cylinder 4 (under the battery on a r107) often didn't have the plug wire properly contacting the spark plug.
I like to use a timing light on the wires to test for consistent or erratic spark on every wire. You don't need to really touch anything. You could put the loop on wire 4 or 8 and do your test of pushing down on the rotor to see if the strobe gets more consistent when you do that.
I suspect that you've known where your problem is all along, in the distributor cap and rotor combination.
Might you have a little wobble in your distributor??
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