SMU - Revised Fuel Injector Balance Test with Tech 2 (Manual Transmission)
| Subject: | Revised Fuel Injector Balance Test with Tech 2 (Manual Transmission) |
| Models: | 2001-2004 Chevrolet Silverado |
| 2001-2004 GMC Sierra |
| with 6.6L Diesel Engine (VIN 1 - RPO LB7) |
This bulletin is being issued to revise the Fuel Injector Balance Test with Tech 2 (Manual Transmission) in the Engine Controls sub-section of the Service Manual. Please replace the current information in the Service Manual with the following information.
The following information has been updated within SI. If you are using a paper version of this Service Manual, please make a reference to this bulletin on the affected page.
Circuit Description
The Fuel Injector Balance Test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical diagnostic trouble codes (DTCs). During the Cylinder Power Balance portion of the test, the engine control module (ECM) turns OFF individual injectors while the engine is running and the scan tool displays engine RPM. The ECM adjusts for the drop in engine speed, so the power contribution of each cylinder must be felt by the technician. If a fuel injector is turned OFF and there is a different power contribution observed when compared to the other cylinders, that cylinder is identified with the complaint. If the customer complaint 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. If a fuel injector is turned OFF and the engine noise or smoke disappears, that cylinder has a fuel injector or engine compression condition.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the majority of the balance rates are positive and high, the dual-mass flywheel is causing a harmonic vibration that is affecting the engine fuel control system.
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A dual mass flywheel concern will cause the balance rates to be inaccurate. The transmission concerns must be repaired before any fuel system diagnostic can be performed.
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The balance rates are only to be used to diagnose these specific concerns.
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The balance rate adjustments are utilized by the ECM only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. A positive value indicates that fuel is being added to each cylinder event, such as with poor engine compression or a fuel injector that is not flowing enough fuel. A negative value indicates fuel being removed from each cylinder event, such as a fuel injector that is flowing too much fuel.
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This step determines if the ECM can control a stable fuel pressure. A high balance rate may be caused by a fuel injector or compression only if the ECM can control fuel pressure.
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The Cylinder Power Balance Test may be performed at any engine speed or load from idle to wide-open throttle. There is a 5 minute time limit for each test. The ECM and scan tool must both be powered down to reset the timer.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check-Engine Controls |
2 |
Are at least 5 of the Balancing Rate parameters more than the specified value? | +4 mm³ | Go to Flywheel Replacement in Engine Mechanical | Go to Step 3 |
3 | Are any DTCs set other than P0300, P0301-P0308? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 4 |
4 | Does the customer concern occur ONLY at idle or during tip-in acceleration off-idle? | -- | Go to Step 5 | Go to Step 7 |
5 |
Are all of the Balancing Rate parameters within the specified range? | -4 mm³ and +4 mm³ | Go to Step 7 | Go to Step 6 |
6 | Graph the Fuel Pressure Regulator. Refer to Fuel System Diagnosis-High Pressure Side. Is the fuel pressure regulator graph normal? | -- | Go to Step 8 | Go to Step 10 |
7 |
Important: The fuel Cylinder Power Balance Test must be performed under the conditions for which the concern occurred. The concern must be duplicated during the test. Important: Do not operate the cruise control during this test. Cruise control reactivation after the test may cause a brief extreme increase in engine speed.
Do any of the cylinders indicate a different cylinder power contribution than the others, or lessen the customer concern? | -- | Go to Step 8 | System OK |
8 |
Important: 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. Perform the Engine Compression Test. Refer to Engine Compression Test in Engine Mechanical-6.6L Do any of the cylinders have low compression? | -- | Go to Symptoms-Engine Mechanical in Engine Mechanical-6.6L | Go to Step 9 |
9 |
Important: Refer to Injection System Components in Engine Controls Component Views. Failure to correctly identify the cylinder positions may result in the replacement of the wrong fuel injector. Replace the fuel injectors on the cylinders that had poor cylinder power contribution, high balance rates, or a noise/smoke change. Refer to Fuel Injector Replacement. Did you complete the replacements? | -- | Go to Step 11 | -- |
10 | Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 | Operate the vehicle under the conditions in which the concern occurred. Does the system operate normally, with no DTCs or symptoms? | -- | System OK | Go to Symptoms-Engine Controls |
