93 deville

My '93 Eldo which has the same 4.9 engine won't run well on regular. You could retard the timing a couple of degrees but you would likely then lose in mileage what you gained at the pump. Some have reported no real difference in performance. You could try some 89 and if you get any pinging you can go back to 93. FWIW YMMV

My 1989 cadillac deville 4.5L ran fine on 89, on 87 is seemed to get quite a bit less mileage.

Rregards, Chance