Cylinder has spark but not firing..
Flip that intake manifold over. On the ends of the intake manifold is what im thinking. Where the runners are. That would be in a place where it could be sucking crank case pressure which would be a vacuum leak as well. Im not dogging that just because its "old" it doesnt work. This intake had a crack in the water jacket when i first got and had to get it welded back. Whose to say there isnt another crack?The reason some of us are on your *** is because you have not indicated that you've taken any real steps, other than "throwing ideas" at the problem.
Your theory that "just because it's old" it's probably cracked does not hold water, no pun intended, neither does your thinking that this is a hidden crack. It might be, but very doubtful
LOOK at this photo of an LD4b:
The cylinders that are paired by the hidden, underlying port runners are 1 - 4 - 6 - 7
On the other side, the UPPER runners are 2 - 3 - 5 - 8 which are on TOP of the lower, hidden runners. How is there going to be a "hidden" crack?
And........if there's a crack in that side, why is only 2 and 8 giving you trouble which are separated at far ends of the engine?
Why wouldn't it be 5 and 8 which are on the same runner?
Or why not 2 and 3, which are on the same runner?
Now anything is possible. But a "warped intake" leaking from the oil gallery would normally show "burning oil" as it's sucking crankcase gases from the valley
