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5.0L (1979-1995) MustangTechnical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.
84 - EGR Vacuum Regulator (EVR) Control Circuit Failure (O) .... which means the EGR controlling solenoid is either open or shorted.... disconnected or snafu'ed + the EEC has deleted the EGR function automatically.