Biogas engines, when turned off, first need to cool down to zero degrees before they can work again.
Not 2+ length.Biogas engines sometime bug out and not draw fuel from their internal tanks (see FAQ)
(Check the internal tab to see if their actually producing power)
Also (as far as I'm aware), engines need to be directly attached to a machine, or run through 2+ lengths of conductive pipe/conduit to transmit power.