Fuel System Air Leak Check

1. Install a transparent hose between the Fuel Injection Control Module (FICM) outlet and the fuel filter inlet.
2. Prime the fuel manager to remove air in the hose.
3. Start and idle the engine, observing the fuel for air bubbles.
^ If air bubbles are not present, stop the engine and Go to Step 7.
^ If air bubbles are present, stop the engine and Go to Step 3.
4. Check the fuel injection pump suction line for air leakage.




4.1. Disconnect the fuel line from the fuel sender in front of the fuel tank (1). Refer to Quick Connect Fitting(s) Service (Metal Collar).
4.2. Plug the fuel pipe (1) using a 1/2 inch rubber plug, and clamp the plug.




4.3. Disconnect the fuel outlet hose (2) from the outlet pipe (1) of the fuel filter/heater element housing.
4.4. Open the drain on the fuel filter/heater element housing and drain fuel into a suitable container.
4.5. Close the drain.
4.6. Install a hand held vacuum pump (3) on the outlet port (1) of the fuel filter/heater element housing.
4.7. Apply 15 in Hg of vacuum to the fuel pipe and observe the gauge reading.
- If the vacuum does not drop, connect the fuel line and Go to Step 5.
- If the vacuum drops, go to step the next step.




4.8. Disconnect the supply line (2) at the engine. Refer to Quick Connect Fitting(s) Service (Metal Collar).
4.9. Cap off the fuel supply line (2) with a 1/2 in. rubber plug (3) and clamp.
4.10. Reapply the 15 in of vacuum and observe the reading.
- If the vacuum drops, repair the leak between the supply line fitting and the fuel filter/heater element housing.
- If the vacuum does not drop, repair the leak between the engine and the fuel tank.
5. Check the fuel sender for air leakage.
^ Remove the fuel tank.
^ Remove the fuel sender from the fuel tank.
^ Remove the strainer and plug the bottom end of the pickup tube.
^ Apply a vacuum to the upper end of the pickup tube.
^ Observe the gauge reading.
- If the vacuum holds (fuel inlet side of sender is OK), install the fuel sender and the fuel tank.
- If the vacuum does not hold, replace the fuel sender, install the fuel tank, connect the fuel pipe and Go to Step 6.
6. Start and run the engine.
7. Observe the fuel for air bubbles.
^ If air bubbles are present, stop the engine and recheck Steps 4 and 5.
^ If air bubbles are not present, stop the engine and Go to Step 8.
8. Remove the transparent hose and connect the hose of the filter outlet to the injection pump inlet fitting.
9. Disconnect the return hose at the injection pump.
10. Install a transparent hose between the injection pump and the hose of the return line.
11. Start and run the engine.
12. Observe the fuel for air bubbles.

IMPORTANT: It is normal to see small amounts of bubbles during snap acceleration.
^ If air bubbles are present, replace the injection pump. Refer to Fuel Injection Pump Replacement.
^ If air bubbles are not present, Go to Step 13.

13. Stop the engine.
14. Remove the transparent hose and attach the fuel return hose at the injection pump.
15. Clean any fuel spillage.
16. Run the engine to check for fuel leakage.