O.k.,this is a common fault unfortunately.One of the active fuel management lifters has collapsed or is not locking in place.This causes a misfire and the ticking noise and is fairly common.GM has even released a bulletin on this fault bulletin number #PIP4568Q.
There is updated programming for the engine computer that has to be done by a GM dealer and the affected lifter(s) need replaced.On some models the AFM shield/engine oil pan has to be replaced with the updated setup.This is also included in this bulletin here.
I own a 2007 with the same engine and dread when this fails on mine which will probably occur soon.The cylinder heads have to be removed in order to replace them and I recommend replacing all lifters when this is done to prevent any future failures that would require the engine to be taken apart again for repair.
The cost can run around $50 per lifter and 12.6 hours labor plus the cost for oil and oil pan if needed as well as engine coolant and an extra hour labor for programming the computer.
This was a great design to save fuel but also a bad design when these fail unfortunately.
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