Have a 1988 f350, 460 motor. On KOEO Test---code 18--Loss of Ignition Diagnostic Monitor signal to the control module/spark output grounded, and Code 33---EGR valve closed/erratic or has insufficient flow. Can someone tell me what this is and how to fix it. besides taking it to a shop, already had it in shop to put in new computer back in fedruary.

Thanks