GM/Detroit 6.5L ENGINE CONTROLS – Fuel Injection System Diagnosis

Always begin diagnosis of the electronic fuel injection system with the On-Board Diagnostic (OBD) System Check before proceeding to any other diagnostics. This will reduce diagnosis time and prevent unnecessary replacement of parts. The On-Board Diagnostic (OBD) System Check will give direction to further diagnostics, such, as Engine Cranks But Will Not Run or a DTC Table. Diagnosis of electronic fuel injection pump, including the fuelinjection solenoid, fuel solenoid driver, injection timing stepper motor and engine shutoff solenoid also starts with the On-Board Diagnostic (OBD) System Check,
If a driveability symptom exists, refer to the particular symptom in the Driveability Symptoms.
Damage to the injection lines including kinking that causes restrictions or leakage could effect driveability or cause a DTC <to-set.

Fuel Pipes and Hoses
The diagnosis of fuel odor may be a condition of a leaking fuel-feed, return pipe or hose. Fuel pipes that are pinched, plugged, or misrouted may cause restricted fuel delivery.

Injection Nozzle(s) Diagnosis
If an injection nozzle is not properly delivering fuel into the pre-combustion chamber of a cylinder, driveability could be greatly effected, or a DTC could be set. If other diagnosis indicates, or if the injection nozzles are suspected of not properly delivering fuel, they should be tested. Typically, a nozzle failure can be detected by using the injector balance test.
Nozzle testing is comprised of the following checks:
• Injector Balance test (performed with scan tool).
• Nozzle opening pressure (see Important statement).
• Leakage (see Important statement).

Injector Balance Test
An injector balance test is performed with the scan tool. This test will properly identify a stuck closed or noisy injector nozzle. Typically, a nozzle failure will fall into this criteria.
1. Install a scan tool.
2. Start and idle the engine.
3. Perform the injector balance test on each cylinder (balance test refer to a specific cylinder). If a suspect nozzle has been located, the nozzle can be swapped with the adjacent cylinder and balance test can be repeated as a check to positively identify a malfunctioning nozzle.
4. Locate and replace the malfunctioning nozzle and glow plug.

Nozzle Opening Pressure Test
Caution: Do not place your hands or arms near the tip of the nozzle when testing the nozzles. The high pressure atomized fuel spray from a nozzle has sufficient penetrating power to puncture flesh and destroy tissue. This may result in blood poisoning. Always enclose the nozzle tip in a receptacle, preferably transparent, in order to contain the spray.
Important: Injector Nozzle Opening Pressure and Leakage tests should only be performed on vehicles 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 tests are not performed to the above criteria.
Important: Each test should be considered independent of the others (for example, when checking opening pressure, do not check for leakage). If all of the following tests are satisfied, the nozzle assembly can be reused. I f any one of the tests is not satisfied, the complete nozzle assembly must be replaced. When performing the injection nozzle tests, refer to the instructions provided with the nozzle tester J 29075-B.
• Position a nozzle tester on a workbench.
• Install one nozzle on the tester fitting.
• Place a container under the nozzle that will deflect the nozzle spray and absorb the test fluid.
• Install two clear plastic hoses (1 in. long) over the leak-off fittings.
• Close the shutoff valve at the pressure gauge.
• Operate the lever of the nozzle tester repeatedly and briskly to fill and flush the nozzle with test oil.
1. Open the shutoff valve at the pressure gage one-quarter turn.
2. Depress the tester lever slowly. Note at what pressure the needle of the pressure gage stopped. The maximum observed pressure is the opening pressure. Some nozzles may pop while other nozzles may drip down (this is not leakage).
3. The opening pressure should not fall below the lower limit of 105 bar (1500 psi) for naturally aspirated engines and 117 bar (1700 psi) for turbo-charged engines for used nozzles.
4. Replace nozzles which fall below the lower limit.


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