This article introduces the sight glass method for removing the fuel Cummins engine suction pipe

 Install a sight glass, Part Number 3375362, in the line.

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Operate the engine.

A small air leak will have a milky appearance. A large air leak will look like bubbles in the fuel.

If an air leak is found, inspect the fuel lines, o-rings, and fittings for damage. Check for loose connections.
Replace the damaged lines or tighten the loose

  Operate the engine at high idle with no load, and check the sight glass.

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  Tighten the hose connections and the fuel filter.
Check the drop tube in the fuel tank for damage.

 Replace any defective parts as required.
Remove the sight glass, and install the suction hose.
Test the engine again for other air leaks.

 Gear Pump Drain Method Remove the gear pump cooling drain line from the check valve, and install a plug in the line.
Install a hose on the check valve and place the other end of the hose in a container.

  Operate the engine at high idle with no load.

 If air is entering the fuel pump suction line, bubbles will be visible in the container of fuel.