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502 EFI, spark coming out of the coil, no spark at the spark plugs

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502 EFI, spark coming out of the coil, no spark at the spark plugs

Old 09-25-2014, 08:21 PM
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Default 502 EFI, spark coming out of the coil, no spark at the spark plugs

So I finally got the engine running couple days ago. In the driveway its been running great. Started it yesterday to do one more check before taking to the marina to launch for a test spin. I ran it for about 5 minutes and was gonna let it warm up a little to check the temps and such and then it just cut off. After that it would no longer start and still has not started, just cranks. It turns out now I have no spark to the spark plugs. I DO have spark from the coil to the distributor cap. We were going down the list of the mercruiser troubleshooting procedure and as soon as i get to the question "does the coil have spark?" I say yes and it just ends and says replace distributor cap, rotor, wires, etc. We replaced the cap and rotor and still no spark to the plugs. Its one thing after the other with this thing lately. Couldn't it only be the wires? We check 3 plug wires for spark on number 2,4,6 and nothing on any of them. Rotor is spinning, we checked that next. BTW again its a '97 502 mpi.
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Old 09-25-2014, 08:28 PM
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The coil wire takes a beating. It sends 'spark energy' 8 times more often than your spark plug wires.

Anyway,

Take dist cap off and turn over motor. You want to see if the rotor is spinning or not. If it's not , the dist shaft broke, or the dist gear broke, or worse, the cam's dist gear broke. (edit in: missed where you said you checked this and it spun. Phew !)

If that's all good - hopefully it is, then it's time for more diag on if just the coil wire, or something like the dist pick up or module is not working.

Oh, don't overlook simple stuff like the Fuses to the EFI, and etc.
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Old 09-25-2014, 08:38 PM
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If you have spark from the coil to the cap, the module and pickup are good and the distributor is turning. If you have spark going into the cap but none coming out on any cylinder, it can really only be the cap or rotor, and way more likely to be the rotor than the cap. How strong is the spark coming out of the coil, it needs to be an extremely strong spark, otherwise you may just have a weak coil and the added resistance of going through the cap, rotor and wires will kill the spark at the plugs.
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Old 09-25-2014, 09:10 PM
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donzi matt, that was actually my next thinking, swap the coil from the port engine and see if its just a coil going bad and not producing enough spark to jump. When we checked the spark it looked pretty good but then again i dunno for sure as I dunno what a weak spark looks like compared to a really strong one.
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Old 09-25-2014, 10:02 PM
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Speaking of weak - I had real weak reading attention on the original post. Doh.

Dull thin spark with click noise vs bright wide spark with clack noise. Hard to tell you difference...easier to show.
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Old 09-25-2014, 10:03 PM
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coil wire or weak coil..
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Old 09-26-2014, 06:58 AM
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Well after work will Def be swapping coils and hope I getbsomewhere.
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Old 09-26-2014, 06:17 PM
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So swaoped the coil, fired instantly. Smh
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Old 09-28-2014, 03:01 PM
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Took it out for a two hour spin out into the ocean today and woo felt great. Amazing weather today.
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