Richard---Let's take the "dropping out" of #6 cylinder in two parts.
First, the spark.
If you can pull off this plug wire and place it's end within 1/8" (3MM)
and spark consistantly jumps the gap over to the tip of the plug
connection, it's fairly safe to say that the plug is still good. (Not
fouled, goes to ground.) If the spark won't jump to this self-made gap,
see if it will jump a gap to the rocker cover, or some other grounded
metal. If it does, it rules out the distributor, and it's wire to #6.
If it turns out that the (even) new plug is already fouled, a temporary
"fix" is to use the hottest plug available, such as the Champion N-14,
or a comparable cross referenced brand. An electronic ignition, such as
an MSD, would probably still fire a fouled plug, but this is not the
answer if the fouling is caused from part 2:
If a valve is not closing, for whatever reason, it wil usually show up
in a compression check. This cylinder would be lower than the others. A
"leaking" valve may also cause the needle to drop rythmically on a
vacuum gauge, connected to an intake manifold vacuum source.
You didn't mention if the loss of #6 comes at idle or at higher rpm's.
If it shows up at 3,000 and above, suspect a broken inner valve spring
on either of these two valves.
If the valve is not closing because it's burnt, changing of plugs will
not make the symptom go away. (It will show up in either or both of the
gauge tests above.)
Poor draining of the oil sent to the rocker shaft can also find it's way
to #6 intake valve. Too much oil, as via a supplementary supply line,
can find it's way down valve guides that are worn.
No matter what the problem turns out to be, it's not a complicated fix.
Look for the clues that fit all of the symptoms you describe, to avoid
over-fixing things. Unless you just like to do these things, as many of
us do!
Dick Taylor
CF11143
L.A.
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