01-04 6.6L LB7 Duramax Diesel Low Power or Poor Fuel Economy - kw no performance poor proactive

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

01-04 6.6L LB7 Duramax Diesel low power and/or fuel economy

If low power or poor fuel economy has been verified on the 6.6L LB7 diesel engine and the SI diagnostics are inconclusive monitor the following Tech 2 readings on a test drive.

1. The MAF at WOT and peak RPM should be approximately 400 G/S.
2. The peak boost reading at WOT and peak RPM should be approximately 33-35 PSI..
3. Monitor fuel rail pressure, the desired and actual pressures should track closely together. If needed compare readings to known good vehicle.
4. Monitor fuel supply vacuum with the Kent Moore vacuum gauge tool number J-44638 at WOT (must be driven at 2800 to 3000 RPM and not performed in stall) peak vacuum should not exceed 10 - 12" of HG.
5. Compare the Intake Air Temperature readings to known good vehicle.
6. Monitor the fuel command value at idle, accessories off, and engine at operating temperature. The normal range is 7-9 mm3.
7. Monitor the fuel command value at 3000 rpm full load (must be driven not tested in shop) with the engine at operating temperature. Normal range is 85 - 90 mm3.
8. Check the fuel quality and fuel API reading.
9. Verify proper APP operation or compare APP voltages to known good vehicle.
10. All comparison readings for low power should be taken from the SAME YEAR, MAKE, AND MODEL VEHICLE.

If the above readings are all normal when compared to the SAME YEAR, MAKE, AND MODEL VEHICLE.

1. Check for oversize tires and verify the vehicle has the OEM tire/wheel size. Oversized tires will cause a perceived lack of power.
2. Small air leaks in the Turbo Air Charge Cooler Hoses can also cause low power. Use the Kent Moore tool J-46091 to determine if there are leaks in the charge air cooler and hoses

NOTE: All engine data readings may vary depending on vehicle build, engine load, and the regional location of the vehicle. If there is a question about a specific engine data reading it should be compared to the SAME YEAR, MAKE, AND MODEL VEHICLE.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

( 01 02 03 04 6.6 LB7 C2 C3 K2 K3 Chevrolet Silverado GMT800) and (01 02 03 04 6.6 LB7 C2 C3 K2 K3 GMC Sierra GMT800)

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