Gjac wrote:
My understanding is if the valve timing jumps, you'll get little or no compression equally in all cylinders, because valves fail to open and close at the right time. What am I missing?
You aren't missing anything there; however, the ignition module only controls the spark timing. It has nothing at all to do with the valve timing, which is affected by a timing chain or belt (if you have an overhead camshaft engine design), or by the camshaft in the engine block via pushrods.
If the gap you're talking about is between the pickup and the magnets on the flywheel: that gap does not affect the ignition timing which is fixed based on where the magnet is on the flywheel and where the ignition module mounts. If you can adjust the module clockwise or counterclockwise, that would alter the ignition timing. Likewise, if the flywheel slipped on the crankshaft (accompanied by shearing its key), that would also throw the ignition timing off. Neither of these in themselves affect the valve timing or compression in the slightest.
