Trouble With My Fuel Filters

[jake15]

i have a 1974 mack single axle rd model. this truck has a scania motor . i have had this truck for 20 years and it has always been very reliable. for the past two years i have had a problem with the truck shutting off on me. when it shuts off the fuel filters will be nearly empty . if i crack a injector line and pump the hand primer for a while it will eventually start and run . it may shut down again in 10 minutes or it may not do it again all day. it will do this both running or at a idle. this truck has 2 tanks , where should i start . i have heard from friends (not mechanics) to look for a tank blockage, the equilizer valve ? a return problem or even the pump . when the truck is running it runs just fine . any ideas would be greatly appreciated. thanks

[HK Trucking]

I suspect an intermittent leak somewhere on the suction side of the system, allowing the transfer pump to suck air instead of fuel.

[Bollweevil]

First make sure the fuel tank vents are open. Then drain the primary filter into a container, and look for a black, grainy substance, similar to fine sand. Sometime with age a rubber lined fuel line will come apart. Part of the line will separate and act like a flap, closing the fuel line under suction. You could disconnect the line at the primary filter, substitute a known good line and run the engine from a fuel can.