Originally Posted by compu_85

My car was doing this because of leaking delivery valve seals...

-J

Originally Posted by jay_bob

The 603 uses mostly standard fuel hose except for these 3 hoses, these have banjo fittings at each end (except for the end at the lift pump output).

(Note the 606 uses the "plug in" hoses with the notorious o-rings in the fittings)

- Lift pump "out" to main filter "in"
- Main filter "out" to IP "in"
- IP "return" to main filter "return"
These 3 hoses are rebuildable but it's much easier to just buy new ones. Don't forget the crush washers. Also be sure to blow out the banjo bolts with brake cleaner while it's apart.

The fuel preheater valve is rebuildable with a rebuild kit. This can be bypassed for the summer months but you will want it next winter.

The remainder of the fuel system is standard 5/8 hose with traditional clamps.

I think you have an air incursion in the fuel system somewhere up front. I would start by rebuilding all these items and see if that doesn't fix it.

Remember that the fuel system operates at a pressure lower than atmospheric on the supply side so if there is a bad seal it sucks in air rather than leak fuel.