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  1. #1

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    Spark Plug Wiring Order

    I have a 1996 Polaris SL780 with engine EC780PWE0213214. The previous owner did not mark which spark plug wire was the front (MAG) plug. I am not sure of the firing order either. My Ebox is mounted on top of the battery if that helps. I rebuilt the carbs and everything, tried to start it up today, and it almost started but seemed like the plugs were out of order. Also, the starter was slowing down, not sure if it was because I was cranking so much, or because my battery is dying. After cranking for so long I was worried about flooding it, but I took the spark plugs off and cranked it a few times and nothing came out of the holes. And there is fuel going to the carbs as I can see it through the lines. Please help!

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    The blue Fuji engines use what's called a wasted spark system. Meaning all 3 spark plugs fire at the same time, but only 1 cylinder will be in the correct position for the spark to ignite the air fuel mix. With a 3 cylinder engine the pistons will be 120* apart, so when 1 is at TDC and needing the spark, one has the piston coming on it's way up, and the other is on it's way down. So the spark in those cylinders does nothing or is "wasted" (hence the name)

    So, realistically, you cannot put the plug wires in a wrong order.

    If you want, you can put an alligator clip on 2 of the spark plug wires and clip them both to a ground. Then install the third plug wire on any cylinder you want and see if it will start (will run poorly, but should run on just 1 cylinder) You can swap cyls and plug wires, but they should all work on any cylinder.

    If you're having starting issues, make sure the battery is fully charged. Make sure the lanyard is installed. And just for an easy fix, you might want to unscrew the spark plug boots from the wires. (yes, they thread on/off) Cut the wires back about 1/4" to expose fresh wire and rescrew the boots back in. This often helps with weak spark.


    If you're using the choke, you can possibly be too rich to ignite, but I highly doubt you will have fuel pool up inside the cylinder from just attempting to start it. (there is no accelerator pump on the blue engine carbs)

  3. #3

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    Yeah so checked the charge of the battery today and it was at 11.6 volts. Going to get a new one tomorrow. I suspect that is the reason I couldn’t start the thing.

  4. #4

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    Quote Originally Posted by Carson99 View Post
    Yeah so checked the charge of the battery today and it was at 11.6 volts. Going to get a new one tomorrow. I suspect that is the reason I couldn’t start the thing.
    DI’d you ever get your ski to start


  5. #5

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    Jul 2020
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    I came across this thread while working on my 96 slt780. As stated above the system is a "wasted spark system" so plug order doesn't matter. But what about coil connection order? The reason I ask is the diagram seems weird the way they are hooked together but all 3 coils are the same.

    Why not hook them in series? Does this even matter since they fire all at once?

    There is plenty of wire length for either configuration to work. Maybe the 3-1-2 order gives a little more wire for ease of connection? Am I just over thinking it?
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  6. #6
    Click avatar for tech links/info K447's Avatar
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    I have no technical understanding that would care how the ignition coils are wired in series.

    I would suspect easier wire dressing and routing would be the reason. And they had to pick some wiring order to be consistent from the factory.

    I will mention that the ‘ground’ side of each coil primary is through the other ignition coil primaries, except of course for the coil which has one side connected to actual ground.

    Often forgotten is that there is also a return circuit for each coil secondary. The voltage that jumps the spark plug gap does not end in the engine cylinder head or the engine crankcase. It continues to flow through the engine and then through the thin black wire back to the electrical box and from there through each ignition coil ‘ground’ wire until it reaches the secondary coil from whence that spark began.

    Electricity flows in a loop. Each spark requires a complete circuit flow, for each primary coil and for each secondary coil.

    With a Fuji blue engine wasted spark system there are six simultaneous spikes of current/voltage flows, with each primary and secondary event going around their own overlapping electrical loop.

  7. #7
    Click avatar for tech links/info K447's Avatar
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    And all of this repeats more than 100 times per second running at WOT on the water.

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