When you replaced the cap & wires, did you match the order they were in, or did you consult a manual? What did the old plugs look like?

A blue spark isn't quite as useful an indicator of adequate firing voltage as you might think - the initial voltage required to bridge the gap while firing is far higher when the plug is under compression. I'd use an actual spark tester connected in-line w/ the wire & plug - especially if you've got weak sparks on other cylinders.

If it won't run on starting fluid, that sort of (but not completely) rules out a fuel delivery problem. Did you check timing with a timing light? Have you checked for vacuum leaks and checked the airflow sensor? Have you taken any vacuum gauge readings?

Did you get any sort of history from the previous owner about how it "died"?

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.