If you have such an adaptor such that it will fit at the glow plug location that is great and use it with the possiblity the glow plug may break. The manual mentions the glow plug bore or the prechamber, my interpetation is the prechamber is the injector threads. For those without an adaptor or a 603 engine then the injectors are the way to go. What does the shop manual say about the engine being hot or cold???

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Brian Toscano