Circuit Description
The fuel injector control module (FICM) enables the appropriate CNG fuel injector on the intake stroke for each cylinder. A voltage is supplied to the CNG fuel injectors through a pair of fuel injector relays. The FICM controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high, or low, will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.
Diagnostic Aids
| • | Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition. |
| • | Perform the fuel injector coil test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions. |
| • | If the fuel injector coil test does not isolate the condition perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
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This step determines if all of the fuel injectors are within 0.5 ohms of each other. If the highest resistance value is within 0.5 ohms of the lowest resistance value, then all of the fuel injector coil windings are OK.
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This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
2 | Observe the engine coolant temperature (ECT) with a scan tool. Is the ECT value within the specified range? | 10-32°C (50-90°F) | Go to Step 3 | Go to Step 4 |
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Important: Calibrate the DMM and test leads to 0 ohms in order to prevent misdiagnosis. Measure the resistance of each CNG fuel injector with a DMM. Refer to Testing for Continuity in Wiring Systems in the J Platform Service Manual. Do any of the fuel injectors display a resistance outside the specified range? | 1-2 ohms | Go to Step 6 | Go to Diagnostic Aids | |
Is the difference equal to, or less than, the specified value? | 0.5 ohms | Go to Diagnostic Aids | Go to Step 5 | |
Did you complete the replacement? | -- | Go to Step 7 | -- | |
6 | Replace the fuel injector or fuel injectors that are out of the specified range. Refer to Fuel Injector Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- |
7 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 |
