So I have a classic rod knock sound but am trying to verify 'better' before I pull the engine. If I unhook cyl 6 ignition coil the knock gets louder. Could that be confirmation? I've seen where the knock stops when you disconnect a plug, but not get louder?
With All (6) Coil Packs installed... if the Knocking Sound is More prominent at Idle... and diminishes as the RPM band is raised (Not Too Fast...and Not Too High) then this would be indicative of Loose Connecting Rod via a Bad Babbitt Bearing. The Definitive Test involves taking a Non-Destructive insertion of either a Slender Brass Rod... or a Screw Driver with the tip and shank wrapped in Gorilla Duct Tape and after removing the COP and Spark Plug... Follow these Guidelines:
It might take a bit of practice...but if you achieve what the VOP in this Video performs... The Con-Rod Bearing will be the Culprit. After you button up everything...please shoot a short video if possible of the sounds emanating from the full length of the upper engine...and from the sides and underneath the areas you can hear the sounds the loudest and link it to Youtube for more diagnostic help from everyone:
I could not get any movement from any piston that looked like that. I'd eventually push the whole Piston down turning the crank. The knock comes under quick revs and once warm enough, at idle only audible under the truck at idle..
Since the sound seems to be drawing your attention to the last cylinder in the bank right at the Firewall, the next place to look would be between the Transmission and the Back of the Engine Block inside of the Bell Housing ...for a Possible Cracked Flex-Plate. Look for signs of having Bad Motor Mounts with evidence of their "Bulbs" being collapsed and a "Black, Sticky Goo" getting ejected on the adjacent areas of the under Wheel Wells.
Just know that this is one possible cause for eventually having a Cracked Flex-Plate. Pull out the S/S Round Inspection Port under the Bell Housing AFTER safely Jacking and Supporting the SUV on Jack Stands and Chocking the Rear Wheels, front and back. Then hold your Cell Phone under that area and record-listen for the rhythmic sounds of any knocking concentrated inside of that area: