Is there some way to diagnos which is the culprit.

The EZL module lists for some $2,500
The coils are only $165 each

While cost is somewhat less, its still tough.

Should I simply try one coil, then the other, then the EZL?

Someone posed the concern that if 1 coil goes bad, it can affect/damage the EZL...and or the other coil??? Is this possible.

With an interrmittent problem such as this, I suspect it make take time to determine if the problem is solved.

LAST BUT NOT LEAST...AND I KNOW THIS IS ONLY A GUESS...
I am going on a road trip this weekend entailing some 900 miles. Should I leave the 500E at home? I.e. will it get progressively worse (occur more often) or will it more likely just fail catastrophically? I can simply buy a coil and carry it with me if I can isolate for certain that the coil is it, but otherwise that only covers 1 of the three candidates.

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dwight