87 Merc Alpha 1 V6 175. Spark knock when throttling down.(High panging noise/ rattle) Runs quiet at idle, runs tight in neutral, pangs loudly when in gear and throttling. Moving distibuter eliminates panging which means the timing isn't advancing with my throttle. Is my Thunderbolt Ignition Box shot? How do I troubleshoot with a volt meter. Thanks TC.
