A professional scanner is needed to check EGR circuit operation.. Did you get the hoses hooked back up to the right ports? Possible blocked passages, pressure sensor (DPFE) or vacuum control solenoid issue but it must be tested to find out!!
RepairPal Certified shops can diagnose and repair your 1997 Ford E-350 Econoline. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.