A clue. The rogue sound is at half the engine rpm. I counted and got 44 in 10 seconds, or 264 in a minute. I didn't have a tach hooked up but that's going to be half speed. So, if my logic is sound and a cylinder fires once ever two revolutions, it's likely piston, or rod (big or little end) related. That said, I'm still surprised I didn't detect a change by pulling plug wires.

RonR


RonR


1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1964 CJ5