Underextrusion with new clean nozzle

Vertex 3D Printer Vertex - Issues while printing
1

I’m struggling with this problem a few days. I printed around 5kg of PLA, equal on each nozzle (i have dual printhed). At this moment i have to print much slower than i print at the beginng to avoid underextrusion.

For example printing infill now 50mm/sec is the limit, before 80mm/sec was not a problem.

I change the nozzle for the new one any there is any difference, i checked long ptfe tubes the are no frictions.

Temperature is also checked, 180 degree and 200 degree gives the same print effect, i made hand test i push filament directly into printhead and it melt like butter (a little bit better on the new nozzle). I printed also a dual fan duct which is mount on the printhead, one fan is cooling the print (factory 25mm) and second (40mm) cool the isolaters. I printed with this around 1kg without any problems at 180 degrees it helps with retraction and canceling stringing effect.

What else can be the cause of underextrusion, except of jammed nozzle and to low temperature?

2

Just a guess.
Check the screw that hold the pulley on the motor.
Make sure it’s tight.

3

Already checked it is tight.

4

Do you always use the same brand of filament? Some need higher temperatures than others. Is it plain filament or a special one?

5

My only other guess would be to check the reference voltage on the driver cards.
If it’s OK then maybe swap it with one of the axis X/Y/Z to see if the problem moves with it.

6

I use the same brand filament all the time. I must check voltage i did’t do that yet.