Colorado 4WD L5-3.7L (2007)
Fuel Injector: Testing and Inspection
Fuel Injector Diagnosis (With CH 47976)
Fuel Injector Diagnosis (w/CH47976)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic Starting Point - Vehicle
* Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provide an overview of each diagnostic category.
Circuit/System Description
The control module enables the appropriate fuel injector pulse for each cylinder. The ignition voltage is supplied directly to the fuel injectors. The
control module 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 too low will affect the 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.
The CH-47976 Active Fuel Injector Tester (AFIT), is used to test the fuel pump, fuel system leak down, and the fuel injectors. Following the User
Guide, CH 47976-11, and the on screen prompts or selections, will indicate the steps required to perform each of the available tests. The tester will
perform all of the tests automatically and display results of the test. The results can also be down loaded for storage and printing.
Special Tools Required
CH-47976 Active Fuel Injector Tester
Component Testing
Fuel Injector Coil Test
1. Observe the ECT Sensor parameter with a scan tool. The engine coolant temperature (ECT) sensor should be 10-32°C (50-90°F).
‹› If the ECT Sensor parameter is not within 10-32°C (50-90°F), go to step 3.
2. Measure the resistance of each fuel injector with a DMM. The resistance of each fuel injector should be 11-14 ohms.
‹› If the resistance of any fuel injector is not 11-14 ohms, replace the fuel injector.
3. Measure and record the resistance of each fuel injector with a DMM. Subtract the lowest resistance value from the highest resistance value. The
difference between the lowest value and the highest value should be equal to or less than 3 ohms.
‹› If the difference is equal to or less than 3 ohms, perform the AFIT Test Procedure.
‹› If the difference is more than 3 ohms, continue with the Fuel Injector Coil Test.
4. Add all of the fuel injector resistance values to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors to
obtain an average resistance value. Subtract the lowest individual fuel injector resistance value from the average resistance value. Compute the
difference between the highest individual fuel injector resistance value and the average resistance value.
‹› Replace the fuel injector that displays the greatest resistance difference above or below the average.
5. Perform the AFIT Test Procedure.
Important:
* DO NOT perform this test if the ECT is above 94°C (201°F). Irregular fuel pressure readings may result due to hot soak fuel boiling.
* Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.
AFIT Test Procedure
1. Turn OFF all accessories.
2. Turn OFF the ignition.
3. Install the AFIT.
4. Turn ON the AFIT and select the vehicle.
5. Turn ON the ignition and perform the Injector Test.
