| Subject: | Revised Surges/Chuggles Diagnostic |
| Models: | 2001 Chevrolet and GMC C/K Pickup Models (Silverado, Sierra) |
| with 6.6L Engine (VIN 1 -- RPO LB7) |
This bulletin is being revised to update the Sensor Inspection. Please discard Corporate Bulletin Number 02-06-04-028 (Section 06 - Engine/Propulsion System).
This bulletin is being issued to revise the Surges/Chuggles Diagnostic in the Engine Controls-6.6L 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.
Inspection
| Action
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DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle seems to speed up and slow down with no change in the accelerator pedal.
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Preliminary Inspection
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| • | Refer to Symptoms-Engine Controls. |
| • | Ensure the driver understands the torque converter clutch (TCC) operation. |
| • | Ensure the driver understands the A/C compressor operation. |
| • | Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List. |
| • | Use the scan tool to ensure the vehicle speed sensor (VSS) reading matches the speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and the speedometer is normal. |
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Sensor Inspection
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| • | Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure with a scan tool. The actual fuel rail pressure should be between 1.0-1.8 MPa. If it is not, inspect for high resistance in the fuel rail pressure (FRP) sensor
circuits of the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. |
| • | Test for an intermittent FRP sensor signal by wiggling the harness between the sensor and the ECM with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool. |
| • | Observe the FRP sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor problem exists. |
| • | Inspect the crankshaft position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. if there is any movement the reluctor wheel retaining bolts are loose. |
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Fuel System Inspection
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| • | Inspect the fuel supply system vacuum while the problems exists. Refer to Fuel System Diagnosis. |
| • | Inspect for a sticking Fuel Pressure Regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above Desired Idle Speed to 50 RPM below Desired Idle Speed. Refer to
Fuel System Diagnosis-High Pressure Side. |
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Additional Inspection
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| • | Inspect the fuel injection control circuits between the engine control module (ECM) and the fuel injection control module (FICM) for a short to a 5-volt reference circuit. |
| • | Inspect the control module grounds for being clean, tight, and in their proper locations. |
| • | Inspect the generator output voltage. Repair if less than 9 volts or more than 16 volts. |
| • | Inspect the vacuum lines for restrictions, leaks, or improper connections. |
| • | Inspect the torque converter clutch (TCC) operation. |
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