Since 2007 I can only remember one occurance of a stuck part of the Glow Plug staying inside of a 617.952. And the guy that posted I don't believe said what he finally did.

Squirting PB Blaster or Kriol (penetrating oils) in to the hole would help to soften up the carbon.

Look at the makers name on the Glow Plug. If they are Autolites the tips that extend into the Prechamber often swell or actually split. I had 2 of the tips swell on mine but was able to pull them out any way.

It would not hurt to remove the Injector and Heat Shield and get a strong flashlight and see what you can inside of the prechamber.

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84 300D, 82 Volvo 244Gl Diesel