Put noodles in a large bowl and cover with boiling water. Let sit 5 to 8 minutes or until tender. Drain then rinse with cold water.
Heat a large wok over medium heat. Add oil and swirl to coat. Add garlic and cook until fragrant (30 seconds). Stir in sambal (start with 1 tbsp). Mixture will spatter so stand back after adding.
Increase heat to medium-high and add sausages. Cook, stirring occasionally, until sausages are light golden (1 to 2 minutes). Add onions and cook, stirring, until beginning to soften but still quite crisp (1 to 2 minutes). Add noodles and soy sauce, stirring to coat.
Make a well in pan. Crack in eggs (push noodles aside if they fall into the center) and cook until whites begin to set (3 minutes). Break yolks with a spoon. Scramble eggs and toss with noodles.
Add white pepper, 1 tablespoons water, the bean sprouts, and crab. Cook, stirring, until bean sprouts are tender-crisp (2 minutes).