Do you need a specific tool?

Only instructions I can find online are installation, so tried just doing them backwards and got stuck at the first point.

Installing the non-drive side crank arm is tightened with an 8mm bolt – it says simply tighten that and it holds the crank on.

When trying to undo it it just does a quarter turn then goes tight again. Is there a cap on the end that needs a specific tool to be removed (like the end cap on hollowtech cranks) ??

No it’s just a bolt…but it should be at 40nm which is quite hard. Put them on myself but have not had to remove mine yet though.

Yes as per akak, it’s a bolt and should undo normally.
Surprised you not had your off already akak (dependant on age) assuming it’s PF30, the E-13 BB bearings are stupidly small. Bearing’s have an inner diamater of 31mm as they use a shield, ala shimano HTII, not 30mm as per everyone elses

Yeah it’s tight but comes undone. Goes loose for about a quarter turn then gets stuck.

Do those tensioning cups/rings need to be loosened off before undoing the bolt?

Don’t believe so, but you simply wind in the APS dial on the non-drive side by hand, though cant see it causing issues, wont hurt to try though. Otherwise just keep apply pressure till the bolt unscrews..

Since I did mine the other week the answer to the 1/4 turn question is that it’s a self extracting bolt, the first movement takes the tension off of the bolt then the second forces the crank away from the axle. Or that was my impression from actually doing it.

The ’14 e*thirteen cranks do require a tool- and ship with one. That said, the standard Park Octalink seems to work much better…