420SE 1990, Engine M116.965, 8 cylinder (Bosch KE system)

Car based in London, UK

Problem
Cylinder number 1 starved of fuel, outlet from distributor partially blocked. Spark plug cylinder number 1 black soot deposit (fuel not oil) all other plugs OK. Very rough idle, mid and high engine speed OK.

Tried
Opened union at top of distributor number 1 cylinder, little change in engine speed, when unions on cylinders 2 to 8 were opened up (one by one) greater change in speed. Checked HT leads and resistors all OK, sparks at plugs all OK, all plugs replaced with on improvement. Good quality injector cleaner used but no improvement. Replaced injector with new one, no change. Fuel filter replaced 8,000 miles ago.

What I think I need to do
Clean fuel distributor, may be a flushing technique could be used, or to strip it down, clean and replace all O rings and seals. Perhaps those who have attempted a solution could relate their experience.

Thank you for any help you can give.

Bill

bill@survivalpower.com

"Cylinder number 1 starved of fuel, outlet from distributor partially blocked. Spark plug cylinder number 1 black soot deposit "

I'm no expert, but if a cylider is starved of fuel, black soot should not be a problem on the same plug. Fuel starvation would result in a lean condition.

Check these images out. Site loads slow.
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

You make a very good point about soot and fuel stavation. I will look at distributor output again.

Thank you