Fuel Injector Diagnosis
Fuel Injector Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Circuit/System Description
The engine control module (ECM) supplies voltage to each fuel injector on the injector high voltage supply circuits. The ECM energizes each fuel injector by grounding the high voltage control circuit of that fuel injector. 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.
When performing the fuel injector balance test, the scan tool will first crank the engine in order to pressurize the fuel rail. The scan tool is then used to pulse each injector for a precise amount of time, allowing a measured amount of the fuel to be injected. This causes a drop in the system fuel pressure that can be recorded and used to compare each injector.
Diagnostic Aids
* Monitoring the misfire current counters, or misfire graph, may help to isolate the fuel injector that is causing the condition.
* 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 customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
Reference Information
Schematic Reference
Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Component Testing
Fuel Injector Coil Test
Verify the resistance of each fuel injector with one of the following methods:
* If the engine coolant temperature (ECT) sensor is between 10-32°C (50-90°F), the resistance of each fuel injector should be 1.25-1.75 ohms.
• If the injectors measure OK, refer to Fuel Injector Balance Test for further diagnosis of the fuel injectors.
• If not within the specified range, replace the fuel injector.
* If the ECT sensor is not between 10-32°C (50-90°F), 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 0.45 ohms.
• If the difference is equal to or less than 0.45 ohms, refer to Fuel Injector Balance Test for further diagnosis of the fuel injectors.
• If the difference is more than 0.45 ohms, 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 difference above or below the average.
Important:
* DO NOT perform this test if the engine coolant temperature (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.
* Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.
Fuel Injector Balance Test
1. Verify the correct low side fuel pressure. Refer to Fuel System Diagnosis (Except Saturn) (Component Tests and General Diagnostics)Fuel System Diagnosis (Saturn Only) (Component Tests and General Diagnostics) .
2. With a scan tool, select the Fuel Injector Balance Test function within the Special Functions menu.
3. Select an injector to be tested.
4. Press Enter to crank the engine, pressurize the fuel rail, and pulse the injector. The fuel rail will be pressurized to 12 Mpa (1,740 psi) before the injector is pulsed.
5. After the injector stops pulsing, record the fuel pressure drop.
6. Repeat steps 3 through 5 for each fuel injector.
7. Perform the Pressure Drop Calculation.
Pressure Drop Calculation
1. Add all of the individual pressure drop values except for the injector suspected of being faulty. This is the total pressure drop.
2. Divide the total pressure drop by the number of fuel injectors that were added together. This is the average pressure drop.
3. Multiply the average pressure drop by 0.20. This is the acceptable variance from the average pressure drop, 20 percent.
• If the difference between any individual pressure drop and the average pressure drop is more than the acceptable variance, replace the fuel injector.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Direct Fuel Injector Replacement (Service and Repair)