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There is a bulletin that deals with this concern. When a AFM lifter collapses the VLOM assembly should be replaced, along with the lifter guides. Check the screen that is under the VLOM ( valve lifter oil manifold) oil sending unit. It may be plugged or slightly restricted.
Here is the bulletin PIP 456K.
Some customers may comment on an SES light, engine misfire on cylinder 1, 4, 6, or 7 and/or tick noise.
This may be the result of an AFM lifter that unlocks as soon as the engine is started or one that is mechanically collapsed/stuck all of the time.
If an AFM lifter unlocks as soon as the engine is started, low compression will be found on that cylinder during an AFM compression test, along with a SES light, DTC P0300, and engine misfires on the related cylinder but it is unlikely that any noise will be experienced.
If an AFM lifter is mechanically collapsed/stuck, low compression will be found on that cylinder during an AFM compression test, along with a consistent valve train tick noise, SES light, DTC P0300 and engine misfires on the related cylinder.
If SI diagnosis does not isolate the cause of this concern, perform the following diagnostic steps as necessary:
|1. ||Perform a Cylinder Deactivation (Active Fuel Management) System Compression Test in SI. If the running compression of the misfiring cylinder stays below 25 PSI regardless of the AFM solenoid being commanded on or off, an AFM lifter is mechanically collapsed/stuck or unlocking as soon as the engine is started.|
|2. ||Perform the Cylinder Deactivation (Active Fuel Management) Valve Lifter Oil Manifold Diagnosis and Testing in SI. If the test above isolated a possible AFM lifter concern, it will lead to this test, which tests the VLOM (Valve Lifter Oil Manifold) for proper operation. SI states a limited amount of air will leak from the bleed holes and outlet ports even when the solenoids are off, compare the amount of leakage to verify all 4 solenoids are operating the same. If it isolates a concern with the VLOM, replace it and reevaluate the concern.|
|3. ||The AFM lifters can also be monitored for proper operation by carefully inspecting the cylinder 1, 4, 6, and 7 rockers and valves while cranking or briefly running the engine with the valve covers removed in the service bay. If the valve(s) of an AFM cylinder stop moving while doing this test, the AFM lifter is causing the concern.|
Notice: If SI diagnosis or any of the steps above indicate that any AFM lifters are unlocking or collapsed as described above, follow the applicable notes below and replace the VLOM, all AFM lifters, and all plastic lifter guides.
On the 2008-2009 Pontiac G8, 2010-2011 Camaro, and 2007-2010 Full Size Trucks with AFM, also determine if the AFM pressure relief valve shield that is listed in the latest version of 10-06-01-008 has ever been installed for anything else. If not, remove the oil pan and install the AFM shield. If the shield has been installed before, disregard this step. Due to oil pan differences, this shield will not fit Passenger Cars with the LS4 engine or Mid-Size Utility Vehicles with the LH6 Engine. It is also important to thoroughly clean the inside of the oil pan while it is removed.
On the 2007-2009 Chevrolet Tahoe with the Police Package, also reprogram the ECM with the latest calibrations. This only applies to Police Vehicles.
Carefully inspect the camshaft lobes through the lifter bores with a pen light or bore scope to ensure that they are not obviously worn. Also inspect the lifter bores for any obvious scoring/damage that could be a concern.
When reassembling, ensure that the lifters are properly aligned to the new plastic lifter guides before they are installed. If they are not aligned properly, it may damage the plastic lifter guide once it is torqued, which may allow the lifter to turn in the guide.
Clean out the related lifter control oil passages (item 1 below) while the old lifters are removed. Generally, it is only necessary to blow through the passages with shop air but if a lot of debris is noted, it may also be necessary to flush the passages out with brake cleaner. The oil should be changed after doing this since the cylinder heads will be off to replace the lifters anyhow.
Low oil pressure to the VLOM can also cause AFM lifter damage. As a result, it is suggested to note the Tech 2 oil pressure parameter at a hot idle. This is located in the Cylinder Deactivation Data List of the Tech 2. Generally most known good vehicles will have around 30 PSI (207 KPA ) of hot idle oil pressure with new engine oil. As long as there are no oil pressure sensor DTCs, such as a P0522 or P0523, the oil pressure sensor is fairly accurate. If the sensor reads 19 PSI (131 KPA) or less while at a hot idle with new oil, also perform the Cylinder Deactivation (Active Fuel Management) Oil Pressure Relief Valve Diagnosis and Testing as outlined in SI and repair as necessary. In some cases, the new VLOM could correct a low oil pressure concern if there is an internal leak or plugged VLOM filter screen.