2007 Silverado Classic "Tap" Syndrome

[Jman423]

While I'm using my buddy's 2007 Silverado Classic (4.8L V8), I'm trying to fix some things up so I can return it in better shape than when I borrowed it.

For years, this truck has sufferered from what I've seen referred to as GM's Tap Syndrome (or some other cute desriptors). The noise is not nearly deep enough to be a knock and it definately isn't a ping... however, it sounds pretty severe as a "tap". The truck can run dozens or hundreds of miles and sound just fine, then, slowly, the tap starts to fade in. Aside from it raising concern and sounding terrible, the engine powers on.

We've tried all of the BS solutions like SeaFoam or Trans Fluid shortly before an oil change as well as clearing the computer both with a handheld and by disconnecting the battery. .

I do have an active CEL for Knock Sensor #2 (if I remember correctly), but I'm told that could be common on these trucks because of damage over time to the harnesses that lead to those two knock sensors. Unfortunately, they are under the intake and mildly pricy. As I understand it, this could be an entirely unrelated issue from the tapping. In some cases, you can tell that the timing is being retarded while the CEL is active to prevent damage.

So, the question is: has anyone had first-hand experience with this beast, and what was your outcome? Any advice?

Thank you
Jimmy

 

[Mooseman]

My 06 Saab with the 5.3 had a "knock" like you describe. Always thought it was piston slap until it developped a rod knock while towing.

 

[mrrsm]

Brian from Briansmobile1 also provides a practical means for diagnosing the loud and sometimes transient "Tap-Tapping" noises evident in a Cast Iron 5.3L stemming from the clogged up oil holes in the trapped and non-removable LS camshaft lifters. The very effective solution he came up with involves doing the following:

https://www.amazon.com/dp/B0002KKIDC/?tag=gmtnation-20

(1) While time consuming, this method obviates having to R&R the Engine Head(s).
(2) Identify which Cylinder Bank(s) is the suspect area via the noise and remove the Coil Packs.
(3) Unbolt and remove the PCV & Booster Hoses & Valve Cover(s), preserving the Rubber Grommet(s).
(4) Unbolt and remove the Roller-Rocker Assemblies and their Push Rods as Original Sets.
(5) Using the Spray Berryman B12 ChemTool, squirt the stuff down each Push Rod like 'straws'.
(6) Saturate each Lifter enough to dissolve the Gas Gum & Junk from within their tiny oil holes.
(7) Allow the Berryman to soak them for around 30 minutes before the reverse re-assembly.
(8) Perform a Cheap Organic Oil & Filter Change, replacing 1 Quart with 1 of ATF or Engine Flush.
(9) Run the Engine afterwards at idle with no Rapid Throttle Bounces for 10-15 Minutes.
(10) Perform the usual Mobil1 Full Synthetic 5W-30 & HQ Oil Filter Swap.


If nothing else... observing Brian here below will provide an example for a sound comparison: