No oil pressure after removing Christen system

Hi,

Question for a friend. He's got a IO-360 and removed his Christen Inverted oil system. Now he's got no oil pressure. Checked for a gauge problem, and it appears fine.

Any ideas for what he should check for?

Thanks.

No oil pres

Check that the plug up where the oil screen goes has been removed to let oil in to the oil pump pickup from the sump.