16a. Combustion Gas In the Fuel Rail Test - Bubble Test

16a. Combustion Gas In The Fuel Rail Test - Bubble Test

Note: Bubbles in the secondary fuel filter bowl indicate combustion gas is leaking into the fuel rail. Combustion gases displace fuel in the fuel rail leading to incomplete injector filling on one or more cylinders. This typically occurs on cylinders adjacent to the leak source on the same fuel rail bank and also appears as low contributing cylinders in the Power Balance Test. Depending on the severity of the leak and the length of time the vehicle has been operated injectors adjacent to the leaking injector or the full bank of new injectors may need to be installed.

Note: Bubbles in the secondary fuel filter bowl indicate combustion gas is leaking into the fuel rail.

Note: The bubble test is used as a screening test prior to carrying out the balloon test. Depending on the leak rate bubbles in the secondary fuel filter bowl can be present even with all glow plugs removed.

Purpose:

The purpose of this test is to check if any combustion gas is leaking into the fuel rail.

Recommended Procedure:

^ Remove the secondary fuel filter cover and the fuel filter.
^ Cycle the key momentarily to raise the fuel level in the bowl and submerse the fuel inlet stand pipe.
^ Disconnect the fuel injection control module (FICM) relay.
^ While cranking the engine~ observe if bubbles are present in the secondary fuel bowl. Bubbles indicate combustion gas is leaking into the fuel rail.

If bubbles are present carry out the Combustion Gas In The Fuel Rail Test Balloon Test to isolate the suspect injector.

If bubbles are not present reassemble the fuel system.

Possible Causes:

^ Low fuel pressure
^ Fuel injector
^ Fuel injector lower 0-ring
^ Fuel injector copper gasket