N14 Base Engine Troubleshooting and Repair Manual – 005-011   Fuel Flow

Loosen the fuel line at the shutoff valve while the engine is cranking. If fuel does
not come out of the connection, the pump
must be primed.

Connect a pressure gauge to the quick disconnect fitting of the fuel pump.

Start cranking the engine and observe the cranking fuel pressure.

If the fuel pressure is below the specification, check to be sure there is a fuel supply to the pump and that it is
not restricted. Refer to Procedure
006-020 in Section 6. Prime the fuel pump if necessary. Refer to Procedure
005-016 in Section 5.

Minimum Operating Pressure

Connect a 0-2068 kPa [0-300 psi] pressure gauge to the quick disconnect fitting to the fuel pump.

Install an 457 mm [18 inch] piece of clear tubing on the suction side of the gear pump or the fuel filter head. Tygon™ R-3603 is the correct size for use with standard Stratoflex™ Number 10 hose fittings.

NOTE: Add the 457 mm [18 inch] piece of clear tubing to the existing fuel suction line. Do
not replace any portion of the suction line to install the 457 mm [18 inch] piece of clear tubing.

Start the engine and allow the air to purge from the clear tubing. No air bubbles can appear.

Shut off the engine and observe the clear tubing.

NOTE: Generally an air space that is drawn from the top of the fuel filter, will appear in the clear tubing.

Observe the fuel in the clear tubing. It
must stop moving within 1 minute if the system is leak free. If the fuel continues to move toward the fuel tank, there is a leak in the system. Observe from which direction air bubbles are coming into the clear tubing. If they are coming from the fuel tank side, the leak is in the cooling plate, fittings, fuel line, or fuel tank.

If the fuel did
not move immediately, let the vehicle sit for about 1 hour. If there is no movement of the fuel, the system is sealed and will
not cause a hard start due to drain-back of the suction lines.

Remove the clear tubing and connect the suction line back to the original connection.