Ball pin in the prechamber is most likely broken and bouncing around. This will beat the filament to death.

Check by removing the injector -- ball pin should be visible as a sphere held in place by two small extensions on the sides sitting directly under the hole in the prechamber.

If broken, it needs to be replaced, and this means pulling the prechamber. You MUST use some special tools to do this, so I'd suggest finding a shop so equiped, it will be cheaper than the tools.

If the prechamber is badly beaten up, it and possibly the injector nozzle will need to be replaced.

If the ball pin is OK, have the injector checked, a bad one can burn the filament off, too.

In either case, you will have noticable injector knock on that cylinder.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!