Visible gaps between adjacent lines, walls thinner than they should be, and layers that do not fuse.
gaps between linesthin wallsmissing materialweak parts
Ordered by how often each is actually responsible, not by how interesting it is. Work down the list.
Cold pull, or replace the nozzle. If extrusion is inconsistent rather than uniformly low, suspect a clog before you touch any setting.
Check speed × layer height × line width against the material max volumetric flow. Over that ceiling the hotend physically cannot keep up, and no flow increase helps.
Too loose slips; too tight crushes the filament oval. Both look identical from the print. Set for light, even tooth marks.
Calibrate e-steps — command 100 mm and measure what actually feeds.
Run the single-wall flow cube and derive it rather than guessing.
Calibration step: Calibrate flow ratio / extrusion multiplier →
Run a temperature tower. Cold plastic is viscous and resists being pushed.