Engine driver passes over eastern line (6)
I believe the answer is:
'engine' is the definition.
(I know that diesel is a type of internal combustion engine)
'passes over eastern line' is the wordplay.
'passes' becomes 'dies' (passes away).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'eastern' becomes 'e'.
'line' becomes 'l' (used when specifying particular lines from a poem).
'driver' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for diesel that I've seen before include "Vehicle fuel" , "Fuel for heavy vehicles like lorries" , "Lorry fuel" , "Motor fuel" , "Type of engine" .)