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. |
Circuit/System Description
The fuel injector balance test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical DTCs. This test uses the Balance Rate and Cylinder Power Balance test to identify cylinders that are not producing the designed power output. The balance rate adjustments are utilized by the engine control module (ECM) only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. The balance rates will change depending on if the transmission is in Neutral or Drive. During the Cylinder Power Balance portion of the test, the ECM turns OFF individual injectors while the engine is running. The ECM adjusts for the drop in engine RPM during cancellation and may not change on the scan tool display. The lack of power at the cancelled cylinder will feel like a misfiring cylinder or vibration. If a fuel injector is turned OFF and there is a no difference felt when compared to the other cylinders, that cylinder is identified with the concern. If the customer concern occurs during idle or during off-idle tip in acceleration, the balance rates are used to identify the cylinder with a fault related to the fuel injector or engine compression.
Diagnostic Aids
| • | The Cylinder Power Balance Test may be performed at any engine speed or load from idle to wide open throttle (WOT). There is a 5-minute time limit for each test. |
| • | A high balance rate may be caused by a fuel injector or cylinder compression only if the ECM can control fuel pressure. |
Circuit/System Verification
Important: If any DTCs other than DTC P0300-P0308 are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
- Start and run the engine until the coolant temperature is more than 82°C (180°F). Turn OFF all accessories.
- Perform the fuel pressure regulator test, refer to Fuel Pressure Regulator Diagnosis.
- With a scan tool, command the Balance Rate Monitor ON. Balance rates should be between +4 mm³ and -6.9 mm³ in Park or Neutral. Balance rates outside the range may indicate contaminated fuel. Refer to Contaminants-in-Fuel Diagnosis.
- Perform the Cylinder Power Balance Test with a scan tool. During cylinder cancellation a noticeable power difference will feel like a misfiring cylinder or vibration.
Important:
• The Cylinder Power Balance Test must be performed under the conditions for which the customer concern occurred. • Do not operate the cruise control during this test. Cruise control may cause a brief surge of engine speed after the completion of the test.
Circuit/System Testing
Important:
• You must perform the Circuit/System Verification before proceeding with Circuit/System Testing. • A fuel injector leak into the combustion chamber may result in mechanical damage to the cylinder. If any fuel spray comes out of a glow plug hole during the compression test, replace the fuel injector of the affected cylinder. • If fuel vapor is emitted during the engine compression test, replace the affected fuel injector and inspect for fuel contamination. refer to
Contaminants-in-Fuel Diagnosis.
Perform the engine compression test. Refer to Engine Compression Test.
| ⇒ | If the compression indicated any of the cylinders had low compression, refer to Symptoms - Engine Mechanical. |
Important:
• Failure to correctly identify the cylinder positions may result in the replacement of the wrong injector. • During replacement of the injectors, inspect the inlet and outlet fittings for corrosion or contamination. Refer to
Contaminants-in-Fuel Diagnosis.
| ⇒ | If the engine did not have low compression on any of the cylinders, replace the fuel injectors on the cylinders that had low cylinder power contribution, high balance rates, or a noise/smoke change during cancellation. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
