Re: #3 & #4 cylinders
Compression test indicates mechanically sound.
All valves are seating, head gasket has integrity, cam is still in one piece.
What do the sparkplugs looking like, compare 1&2 to 3&4.
I doubt vac leak, you would see gas stain below manifold. If not running out.
Is it possible plug wires are crossed 3&4?
John
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