SRG963
10-09-2008, 12:05 PM
Found this info, straight from GM:
#PIP4499: Short Duration Lifter Tick Noise On Cold Or Hot Restart - Aerated Oil In Filter
Condition/Concern:
Some customers may comment on a short duration lifter tick noise that occurs after start up and can last for up to several minutes. This may be the result of air in the high pressure chamber of the lifter affecting valve train lash. When this occurs, valve closing velocity is increased, which causes the noise. Air can be present in the lifter at shutdown due to an aerated oil condition, or it can be ingested into the lifter during a cold start. Oil aeration level, oil viscosity, time to achieve oil pressure, engine speed, and lifter design all play a part in whether lifter noise is observed. Once air gets into the high pressure chamber, it will slowly be expelled through the very tight clearance of the plunger and body.
Recommendation/Instructions:
If the SI diagnostics do not isolate the cause of this concern, perform a cylinder power balance test with the Tech 2 while listening to the noise.
If the noise is eliminated, or is greatly improved, each time a specific fuel injector is cancelled, there is most likely a concern with the clearance of the related piston pin or piston to cylinder wall.
If there is no change in the noise when canceling the fuel injectors with the Tech 2, the noise is most likely a result of the lifter concern described above. GM product engineering is continuing work with the lubrication group and the lifter suppliers to improve the robustness of the lifter hydraulic system. New lifter designs are currently under evaluation and this P.I. will be updated with additional information as soon as these updated lifters are available in GMSPO. In the meantime, replacing the lifters with the ones in GMSPO stock may repair this noise in many instances.
Please follow this diagnostic or repair 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.
#PIP4499: Short Duration Lifter Tick Noise On Cold Or Hot Restart - Aerated Oil In Filter
Condition/Concern:
Some customers may comment on a short duration lifter tick noise that occurs after start up and can last for up to several minutes. This may be the result of air in the high pressure chamber of the lifter affecting valve train lash. When this occurs, valve closing velocity is increased, which causes the noise. Air can be present in the lifter at shutdown due to an aerated oil condition, or it can be ingested into the lifter during a cold start. Oil aeration level, oil viscosity, time to achieve oil pressure, engine speed, and lifter design all play a part in whether lifter noise is observed. Once air gets into the high pressure chamber, it will slowly be expelled through the very tight clearance of the plunger and body.
Recommendation/Instructions:
If the SI diagnostics do not isolate the cause of this concern, perform a cylinder power balance test with the Tech 2 while listening to the noise.
If the noise is eliminated, or is greatly improved, each time a specific fuel injector is cancelled, there is most likely a concern with the clearance of the related piston pin or piston to cylinder wall.
If there is no change in the noise when canceling the fuel injectors with the Tech 2, the noise is most likely a result of the lifter concern described above. GM product engineering is continuing work with the lubrication group and the lifter suppliers to improve the robustness of the lifter hydraulic system. New lifter designs are currently under evaluation and this P.I. will be updated with additional information as soon as these updated lifters are available in GMSPO. In the meantime, replacing the lifters with the ones in GMSPO stock may repair this noise in many instances.
Please follow this diagnostic or repair 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.