The nipple on top of the injection pump for the return was my problem after putting the tank and replacing the lines to the tank, the ip was new so that wasn’t the problem but the return check valve even through it seemed clear and I could see through it , it needed more pressure than the pump to open it. Took a Allen wrench and punched it out of there and then blew it out. I installed it back on an put there,….. it fired right up. Hit me back if you need more help and I’ll walk you through it