Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Diagnostic Fault Information
Cylinder | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
First Reading | 290 kPa (42 psi) | 290 kPa (42 psi) | 290 kPa (42 psi) | 290 kPa (42 psi) |
Second Reading | 186 kPa (27 psi) | 165 kPa (24 psi) | 179 kPa (26 psi) | 200 kPa (29 psi) |
Amount Of Drop | 103 kPa (15 psi) | 124 kPa (18 psi) | 110 kPa (16 psi) | 90 kPa (13 psi) |
Average Range: 156-176 kPa (22.5-25.5 psi) | Injector OK | Fuel Injector - Too Much Pressure Drop | Injector OK | Faulty Injector - Too Little Pressure Drop |
Circuit/System Description
The scan tool is first used to energize the fuel pump relay. The fuel injector tester is then used to pulse each injector for a precise amount of time, allowing a measured amount of fuel into the manifold. This causes a drop in 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 balance test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions. |
Reference Information
Schematic Reference
Description and Operation
Scan Tool Reference
Control Module References for scan tool information
Special Tools
J 39021 Fuel Injector Coil and Balance Tester
Component Testing
Fuel Injector Balance Test with Special Tool
- Ignition ON, verify the scan tool engine coolant temperature (ECT) parameter is less than 94°C (201°F).
- Ignition OFF, install the fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal.
- Ignition ON, verify the fuel pressure is within 262-303 kPa (38-44 psi).
- Monitor the fuel pressure gage for 1 minute. Verify the fuel pressure does not drop more than 34 kPa (5 psi).
- Connect the J 30921 tester to a fuel injector with the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
- Command the fuel pump relay ON with a scan tool and record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the first pressure reading.
- Energize the fuel injector by depressing the Push to Start Test button on the fuel injector tester. Record the fuel pressure indicated by the fuel pressure gage after the fuel injector has stopped pulsing. This is the second pressure reading.
- Add all of the individual pressure drop values in order to calculate the total pressure drop. Divide the total pressure drop by the number of fuel injectors in order to calculate the average pressure drop. The difference between any individual pressure drop and the average pressure drop should not be more than 20 kPa (3 psi).
| ⇒ | If greater than the specified range, allow the engine to cool before proceeding. |
| ⇒ | If the fuel pressure is not within the specified range, refer to Fuel System Diagnosis for further diagnosis of the fuel system. |
| ⇒ | If the fuel pressure decreases more than the specified range, refer to Fuel System Diagnosis for further diagnosis of the fuel system. |
Caution: Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding.
Note:
• Repeat this step for each fuel injector in order to obtain a pressure drop value for each fuel injector. • The fuel pressure may rise after the fuel injector stops pulsing. Record the fuel pressure value immediately after the fuel injector stops pulsing. DO NOT record the higher fuel pressure value.
| ⇒ | If the difference between any individual pressure drop and the average pressure drop is greater than the specified range, replace the fuel injector. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
