SHIELD 2Y3959 - Caterpillar

All 3304 And 3306 Engines Equipped With A Sleeve Metering Fuel System And A Return Line To The Fuel TankAll 3304 and 3306 Engines equipped with a sleeve metering fuel system and a return-to-tank fuel line have a 4N1828 Elbow in the fuel injection pump housing. The 4N1828 Elbow has a check valve inside which controls the rate at which fuel flows back to the fuel tank. When the check valve adjustment screw is installed too far into the elbow, the force of the spring will not let the plunger come off the seat. When the plunger is against the seat, fuel can not flow to the fuel tank. This will cause air to become trapped (held) in the fuel injection pump housing. This restriction can make the fuel become hot and cause a loss of power.
The fuel must flow by the check valve at an approximate rate of 9 gallons per hour (34 liters per hour), when the engine is at normal operation rpm. If the flow rate is less than the rate given, back the adjustment screw out until the fuel flow rate is correct.
4N1828 Elbow and Check Valve. To check the flow disconnect the return line to the tank and let the fuel flow into a separate container. A nine gallon per hour flow rate will fill a quart or liter container in less than two minutes.