Diesel Bombers - fuel pump issue help!

hey guys, so a friend of mine has an 02 cummins and he bought a raptor 100 gph frrp. well come to find out, he has an in tank pump on his truck so we just put off installing the raptor until we had enough time to drop the tank and pull the old pump out. well the other night, a code showed up on his truck "p0253". we didn't want to wait any longer so we just went ahead and installed the pump. we didn't remove the in tank pump hoping it would be okay until we had enough time to take it out. well we got the raptor in and went to bleed the system and no fuel was getting to the raptor and the truck wasn't getting any fuel. but we could hear the raptor pump running. do you guys know anything about this or have had this situation before. please let me know if you have any information.