That may be simular the later Fed , pre OB-2 led set-up
[ 94-95 E320 type].
A 4 blink code is Air Injection system[ air pump] inoperative.
Check the plug/fuse for starters.
May even be disconnected.

PS
Was down in Citra last Sunday and wish it had been weekday so I could have visited Steve B in Gainsville. Next time.
Arthur