Sounds like you have an air leak somewhere in the fuel line between the supply pump and your switching valve. Maybe more. I had similar trouble with my 86 when my fuel cap vent plugged. Check the caps though not as likely. The sending units on these rot often and provide a nice sized air leak too at the elbow part on top. One other thing on that year truck is your water separator on the firewall, you pull it to drain it and it leaks afterwords, very common. I have disconnected mine and replaced rotted lines with plastic air brake tubing...this is nylon inside and not much seems to bother it. It' been on my furnace for 10 years! Lol If you get good fuel, and change your fuel filter around the fall season, you should be fine without your separator. Hope this helps!
A
abediesel at Y!
A
abediesel at Y!