O5 Summit 1000 SDI, no spark

I recently picked up a pair of sleds. A 2005 Summit Highmark, 1000 SDI with 207 mi and a 2005 Summit Adrenaline, 600 HO, DPM with 116 mi. Both. machines are super clean and have sat for a couple years.
I replaced both batteries and got both sleds up and running. After a couple starts, warm ups and shutdowns, on the 1000 Summit, I started the machine, let it warm up and then was revving it up a bit. After a couple revs, it backfired and died and would not start back up. Now it has no spark at all. Every thing else seems to work as normal, it powers up, fuel pump, primes, starter turns machine over strongly, has fuel to cylinder, but has no fire. I checked all fuses and have not found any blown. Looking for ideas of where to look or how to troubleshoot......Thanks

changed plugs after it backfired and no spark, initially.
with Kill switch on or pulled out to start and DESS key on, the machine turns on, fuel pump runs, gauge and lights , come on and starter turns engine over, but there is no visible spark from plugs, when grounded to head. no spark what so ever.
I checked all fuses in fuse box and none are blown, fuse on Battery is not blown.
is there possibly a hidden fuse that I'm not seeing?

So went out and turned the engine over, and lo and behold, the sled was getting spark.
Put the plugs back in and it tried to fire up a couple times then nothing. Puled the plugs back out turned it over and no spark again, then turned it over again and one plug getting strong spark and the other a weak spark then another try little to no spark. It just kept going back and fourth between no spark to one sid strong one side weak.
Could the coil be bad or going bad?
Would the coil cause that symptom with the spark?