Ground to a halt, could do with some help to get going again viz 14 down 3-1-5 - very much thanks to old fashioned "zip" , posh car appears in time G??-?-???Y; 15 across (9) finish off jazz in Catholic Church, interrupting to squeeze backing musicians ??E???R?M and 28 across (7,4) signing agreement to drop power generator in the ocean? ????ING, ?U?K - I had thought about passing (the) buck but cannot see how it relates to the clue. Can anyone throw light on any of these?