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GM/Detroit 6.5L ENGINE CONTROLS – Nozzle Leak Test

Caution: When testing nozzles, do not place your hands or arms near the tip of the nozzle. The high pressure atomized fuel spray from a nozzle has sufficient penetrating power to puncture flesh and destroy tissue and may result in blood poisoning. The nozzle tip should always be enclosed in a receptacle, preferably transparent, to contain the spray.

Important: Injector Nozzle O pening Pressure and Leakage tests should only be performed on nozzles with high mileage, engines that have been over heated or on vehicles that pull heavy loads. False or inaccurate readings can occur if the following test are not performed to the above criteria.
1. Open the shutoff valve at the pressure gage (1 turn).
2. Blow dry the nozzle tip.
3. Depress the lever of the manual test stand slowly until the gage reads a pressure of 95 bar (1400 psi). Observe the nozzle tip. A drop may form on the end of the nozzle but should not drop off within a period of 10 seconds.
4. Replace the nozzle assembly if a drop fails during the 10 seconds.

Fuel Return System Diagnosis
Any restriction in the fuel return system could greatly effect driveability. If other diagnosis indicates or the fuel return system is suspected of being restricted, it should be tested.
1. Disconnect the hose of the fuel return line at the fuel sender.
2. Disconnect the hose of the fuel return line at the injection pump, and connect a vacuum pump with gauge to the hose.
3. Apply vacuum to the return line and observe the gage reading
• If vacuum does not build and hold, Go to Step 4.
• If vacuum builds and holds, repair the return line restriction.
4. Connect the fuel return line at the injection pump and fuel sender.
5. Clean any fuel spillage.
6. Run the engine to check for fuel leakage.


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