Collapsed lifter 06 Chevrolet Trailblazer 5.3L DOD engine. Cylinder #1 misfire code P0301 with lifter noise. Upon removing drivers valve cover I found no movement on the intake valve rocker. I have searched to see if this is a common problem on the DOD engines and there is very little information available. The lifter was collapsed completely. The dealer stocks new lifters but there is no advice as to replace all lifters or just the failed one. Is this a common issue with this engine?

This type of noise is usually caused by malfunctioning valve lifters or an exhaust manifold leak. If the noise lasts for more than a minute and completely disappears or dimishes after the engine is warm, the most likely cause is an exhaust manifold leak. If the noise only lasts for a few seconds, the most likely cause is a valve lifter malfunction. You should start your diagnosis with a visual inspection of the exhaust system. Inspect the exhaust manifolds for leaking gaskets or cracks. Black soot marks where the manifold mates to the cylinder head are key indicators of an exhaust manifold gasket leak. Inspect for broken exhaust manifold bolts. Inspect the gasket area where the manifold bolts to the exhaust pipe. Small exhaust leaks can often self seal once the metal engine parts are heated and expanded.
If there are no signs of an exhaust leak and the noise dissipates a few seconds after starting the vehicle, you should suspect an oil control or valve lifter malfunction. Hydraulic valve lifters use the engines oil pressure to expand the lifter which provides a zero valve lash clearance. This prevents the valves from tapping. When the engine is shut off, a valve and spring in the lifter keep it expanded and retain the oil within the lifter. If the valve or spring allows the oil to drain from the lifter, it will collapse. Upon start up, the lifter will take a few moments to "pump up" and expand as the oil pressure builds in the engine. During this time, the valves may tap since there is clearance between the rocker arm and lifter..

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the P0401 code has to do with your exhaust! Could be caused from sensor to clogged exhaust! The P0301, I believe is misfire, cylinder #1

upper engine knock can be caused by a worn cam shaft worn lifters, although this is usually a ticking noise. piston skirt collapse which can sound like its in the upper engine. a bad wrist pin even a valve hitting the top or the piston like carbon build up on top of the piston.

this code is telling you that cylinder 1 is misfiring. it could be caused by a bad plug, plug wire, bad valve, camshaft lobe, lifter or bad compression in cyl 1.

misfire on cylinder number 1
P0300 multiple misfire
p0301 THE 1 FOR CYLINDER 1
P0302 THE 2 FOR CYLINDER 2
AND SO ON

Yes the lifter or one of the valves could be damaged. No the valve cover and maybe the cylinder head would need to be removed to repair depending on what the actual problem is.

Cylinder #1 misfire. If the engine is running fine the code will reset on it's own after 40 cycles of the ignition key. If the engine is running poorly it could be due to bad spark plug or coil pack.

Bad fuel injector #7 cylinder

P0300 Random/Multiple Cylinder Misfire Detected

P0304 Cylinder 4 Misfire Detected

If a cylinder is not firing it could make that noise. Check/replace your plug wires use dielectric grease in the boot connections. Could be a bad plug as well but I would guess a bad plug wire...

Get the heads worked on or replaced it might need a valve lashment.