Hi
I have a similar V8 version MPI. On these mpi, the diz cap is a known issue. If you have the same it will also be. It’s the flat crab shaped diz cap that has the issue. As far as my experience goes, it caused by condensation gathered during winter storage and sometimes just that the caps are poorly made or designed at least.
With the usual condensation problem, during storage the cap tends to gather moisture in it and cause a surface coating or even corrosion on the terminals. If it doesn’t cause issues at spring start up time, it likely will soon after. Occasionally even if it visually seems ok. I’ve been through a few caps now. Mostly caused by this reason, but one time a brand new replacement cap fitted mid season just failed for no apparent reason all together.
Best thing to do is crack open the cap before storage and spray wd 40 in there and leave it open...even then keep a spare one if you use the boat at sea or far from help.
At the very least, do this and change it every 2 years. My advice anyway.
I also have a sneaking suspicion that some failures are also caused by not fitting the cap perfectly down before tightening the two screws. If you aren’t careful it’s easy to think the cap is in position and tighten screws...but it’s not quite and you end up cracking the cap when tightening. I’ll own up to this once !!