I am experiencing a problem with d2 backflow into the wvo tank. 2002 F-250 7.3L. I have ordered and installed new check valve and purge solenoid but problem still remains. Both return and feel line are flowing diesel when unhooked and running on d2. Switching over to auto mode seems to be pulling wvo back to d2 tank. Filter and screen filter were just replaced, successfully ran tank of wvo a week or so prior to problem. Any suggestions are appreciated. Or possibly a how to temporarily disconnect v3 so that i can run on d2 only. Thanks.