have replaced injectors and orings. fuel filter take top off bleed air out runs fine till fills with air again. What could be causeing this issue???

 

Air is getting in through the suction side of the fuel pump. It could be a poor seal at the tank where the lines connect to the tank or possibly a hole in the pick-up tube inside the tank. If you can insert a piece of clear tubing into the suction side line , which won't be easy with the locking connectors at the connections, you would be able to confirm/isolate the source of air entering the system.