blobby and stringy

I am printing a box that is 52mm high in PETG. I am printing the first layer at 250°C for the heat block and 120°C for the bed then lowering the heat to 230°C for the heat block and 65°C for the bed. I am printing at 100% infill. This has worked well for me up to this time, but I have only been making flat models.

With this box I kept my old settings. The bottom printed well, but after the walls reached higher than 5mm, they were becoming stringy and blobby and hollow. (See attached.) Above 5mm the walls became flimsy. Can anybody give me an idea about what I am doing wrong?

Thank you,

Stuart

You are not extruding properly, possibly due to the temp being too low.
You should see a lot of chewed filament in your extruder too as this amount of underextrusion should leave visble evidence, unless your extruder is slipping (grub screw, bad hobbed bolt....).