Holes in top layer of model, makes my students melancholy

I am running a Powerspec 3D Pro (private label clone of Flashforge Creator Pro) with 1.7 ABS, .2 layer height, 50 speed. I use maker desktop software. I am getting holes in the top of my prints. I just finished the pyramid below to check all of the flat surfaces a pyramid can offer. All of the parts print well except for the top. Things I have tried are

• Infill from 15% (my default) up to 70%
• Speed down to 30
• temperature from 225 to 240 in 5 degree increments
• minimum layer time of 15 seconds (from the default of 5)
• Cleaned nozzle to make sure there wasn't obstruction

Not much difference found from my changes. I have this problem across multiple models using multiple colors of filament. Things I have considered:

• Under extrusion. However, all surfaces other than top layer print fine.
• More fans? This model has a 40mm fan that blows on the hotend.

Any suggestions would be welcomed. Please help

.Attachment 7712

Either something strange in the STL file, or the slicer is making errors (assuming that the slicer settings are OK)?

Which slicer are you using?

Am using the built in slicer in MakerDesktop, they use makerbot slicer. I have tried different infills and layer heights to see if I could shake something loose in the slicer. Guess I could load replicatorG and see if that changes anything.

it does this on every model, not just a specific .stl file.

Nathan

Could it be something with X offset? Possibly raising the hot end between layers? Any feedback?