PIP4568P Tick Noise And or Misfires On AFM Cylinders 1 4 6 And or 7 - (Oct 30 2013) Driveline Control 4WD Driveline Control - part 2
Notice:If SI diagnosis or any of the steps above indicate that any AFM lifters are unlockingor collapsed as described above, follow the applicable notes below and replace theVLOM, all AFM lifters, and all plastic lifter guides.Reprogram the ECM with the latest calibrations if you are working on a 2008-2009 FullSize Truck/SUV or a 2007-2009 Chevrolet Tahoe with the Police Package.On the 2008-2009 Pontiac G8, 2010-2011 Camaro, and 2007-2010 Full Size Trucks withAFM, also determine if the AFM pressure relief valve shield that is listed in thelatest 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. On Passenger Cars with the LS4 engine, determine if the updatedoil pan gasketthat is listed in the latest version of 11-06-01-007 has ever been installed. Ifnot, remove the oil pan and install this updated oil pan gasket. It is also importantto thoroughly clean the inside of the oil pan while it is removed. Due to oil pandifferences, this shield and gasket will not fit Mid-Size Utility Vehicles with theLH6 Engine.Carefully inspect the camshaft lobes through the lifter bores with a pen light orbore scope to ensure that they are not obviously worn. It is suggested to rotate thecrankshaft and camshaft so the entire circumference of all cam lobes can be inspected.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 plasticlifter guides before they are installed. If they are not aligned properly, it maydamage the plastic lifter guide once it is torqued, which may allow the lifter toturn in the guide.Clean out the related lifter control oil passages (item 1 below) while the old liftersare removed. Generally, it is only necessary to blow through the passages with shopair but if a lot of debris is noted, it may also be necessary to flush the passagesout with brake cleaner. The oil should be changed after doing this since the cylinderheads will be off to replace the lifters anyhow.Low oil pressure to the VLOM can also cause AFM lifter damage. As a result, it issuggested to note the Tech 2 oil pressure parameter at a hot idle. This is locatedin the Cylinder Deactivation Data List of the Tech 2. Generally most known good vehicleswill have around 25 PSI (172 KPA) or greater oil pressure at a hot idle with new engineoil. As long as there are no oil pressure sensor DTCs, such as a P0522 or P0523, theoil pressuresensor is fairly accurate. If the sensor reads 19 PSI (131 KPA) or less while at ahot 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 aninternal leak or plugged VLOM filter screen.
ADDITIONAL SI KEYWORDS:
removal replacement installation
Please follow this diagnostic or repair process thoroughly and complete each step.If the condition exhibited is resolved without completing every step, the remainingsteps do not need to be performed.
GM bulletins are intended for use by professional technicians,NOT a "do-it-yourselfer". They are written to inform thesetechnicians of conditions that may occur on some vehicles, or toprovide information that could assist in the proper service of avehicle. Properly trained technicians have the equipment,tools, safety instructions, and know-how to do a job properly andsafely. If a condition is described, DO NOT assume that thebulletin applies to your vehicle, or that your vehicle will havethat condition. See your GM dealer for information on whetheryour vehicle may benefit from the information.
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