Had that on our 8430 twice. I first changed the fuel filters, that didn't help, it kept getting worse. Then they changed a check valve on the fuel rail that they thought was leaking. It helped for a few days, then it came back worse than ever. They were going to put a new fuel pump on it, but instead tried just the flow control valve off the new pump on the old one. After putting on about 800 acres of anhydrous, no problems.