On my 99 pete my fuel is returning to my left tank once in a while from the right tank so I clean the vents and it helped for 2 days then it started to do it again. So I closed my left tank off from the suction side and ran on my right tank I noticed my fuel pressure gauge was bouncing around from 75 to 50. Psi. But my fuel started to return again. I don't know if I have a collapse fuel line or what it could be.