w:

Give this a try.
1) Ensure that there is correct compression in #6.
2) Ensure continuity, and non-leakage of the #6 plug wire, i.e., not grounding.
3) Ensure that #6 spark plug is in good condition, i.e., not shorted internally.
4) Ensure continuity of secondary circuit from #1 plug connector to #6 plug connector.