1996 E 350 stalls

"rck1953"]when your driving down the road it stalls. Leave it sit for 15 to 20 minutes and it restarts. Also when you try to get trouble codes with a scanner the scanner says that it does not recieve information from the computer. We tried to retrieve codes from the OBD 2 port also tried the global from OBD2 it said the same tried to retrieve codes from the OBD 1 under the hood and it said it cant retrive information from computer. I have found that thi OBD 2 port is non functional only the OBD1 will retrieve codes manually and the one I get is for low voltage on egr. Also changed PCM relay and it still stalls if you try to start it before 15 - 20 minutes has passed it fires off once doesnt start. Once it has restarted if you leave it run it doesnt die again until you have shut it down. Thank You