mystery valve on 6.5l td
 

hey guys. I have a valve on top of my engine located next to the alternator. its a screw in and out on/off valve. it has two hoses. one just hangs off the driver side of engine and the other goes under the intake. I turned it off while m truck was running and it died. so what does this valve do cause I opened it back up and she still wont start. the filter housing runs out of fuel but Ive already put 5 gallons throught the housing and as soon as it runs out she dies. any ideas?

It's a drain for fuel system,if your truck died when you opened it then you need a new lift pump our your wiring to pump has a issue.

Water in fuel drain for filter housing.

ok when I open it now fuel comes out then I close it and then the truck runs but then filter housing runs out of fuel. Any ideas?

The oil pressure switch powers the lift pump when the engine runs and the LP relay powers it when the key is turned to crank-so it would seem that your OPS is bad(provided the LP works when cranking)and that is a common problem.

For a test open the filter bleed screw,then put the truck in drive and turn the key to crank watching through the open hood-fuel should jump out the filter bleed when the key is turned.
If so the LP is ok and OPS needs replaced likely-AC Delco ONLY for replacement because parts store OPS are often bad right out of the box.

Google "OPS relay mod" and install for long tern reliability.