The first thing is to check if both plugs are not firing or only one.
#1 The SDI uses a dual ignition coil like the E-TEC, so you need to check spark on both plugs.
#2 The ignition coil pack is robust.
#3 There is no known power connection issue with the Ignition Coil that I am aware of.
#4 If there is spark on one plug and not the other, then it is likely a connection issue, hopefully with a corroded/rotted plug wire or boot. Another possibility is arc'ing which is visible in the dark. The two other possibilities are an open in the ignition coil or an unseated wire at the ECM A plug. A problem with the last two will eventually cause the ignition coil driver in the ECM to fail. Any of the problems listed in #4 can be rooted out by swapping the coils at the connector. Sine there are two drivers in the ECM, and two ignition coils, one switch of the igntion coil wires will determine what component has failed, the driver or ignition coil.
#5 If there is no spark on both plugs, the CPS or wires to/from the CPS is likely at fault. Disconnect the CPS plug and test for 190-300 ohm at rest, and 1-2 Vac while cranking over the engine with the pull cord. If both results are good, then plug the CPS, disconnect the ECM A plug and repeat the two tests. Also make sure there is no sign of the two ECM A terminals being unseated. It will be pin #5 Yellow/White wire, and pin# 19 Blue/Yellow.
If the resistance test passes, but the voltage test fails, then there is something obstructing the CPS sensor. Remove the Magneto Flywheel for a visual inspection. Broken flywheel magnets are a real possibility, and it has happened that a piece of shattered earth magnet was caught on the CPS and no longer provided voltage.
In another case I troubleshooted with good resistance, the voltage and spark were sporadic/intermittent. The magneto flywheel was removed with no visible problem, leaving the crankshaft runout as the only possible cause. It is easy to diagnose by turning the engine over and looking at the distance between the CPS and triggers. Spec is ~ 0.028" +/- which is not in any SDI or E-TEC shop manual. Spec is found by measuring different sleds and looking into older shop manuals. Note that I did not provide a specific +/- . This is because it is not that important. Closer is no problem as long a it does not touch the triggers. Farther is ok as long as the sensor still reads the
#6 This diagnostic list works for the 600/800/1000 SDI as they all work the same. The 600 has an inherent issue with the CPS due to the location of the plug. The 1000 has a slightly different harness configuration for the CPS plug and seem less prone to failure, but it is a possibility to keep in mind.
#7 The 30A fuse socket I covered in one of my previous replies. The last time before I applied a permanent fix, it generated a Relay Coil Wine. Getting that kind of resonance is rare and probably be difficult to reproduce. I have only seen it one other time, years later on DooTalk and knew right away by the owner's description of a buzzing sound (click here for the case). Twice in 9 years with the first one being my own, so I doubt anyone will hear about this again for some time. However, this type of problem, even if it does not cause a coil wine, affects the relays which in turn creates radicals/surges in the ECM and other components. If a relay keeps burning, the voltage at the relay coil needs to be measured/monitored to find what is causing the power issue.
Also use a sealed relay for a permanent repair.
Click here for a thread on where to acquire quality oem relays.
For Relay Troubleshooting,
click here. This was for a 2011 800R E-TEC which had only one relay before BRP integrated the Battery Charging Relay into the ECM. BRP did this to eliminate failure points. BRP even deleted the fuse box with the fist MY2009 of the E-TEC, only to return with a sealed fuse box with the first G4 850 for MY2017. it is not something we need to change, buy rather to keep in mind. For example using dielectric grease for connections and applying a sealant for the splices will accomplish the same goal.