1997 50HP 3cyl coil test question

[bleb]

J50DTLECA motor
My motor will not rev past about 3000rpm (previous thread) and I finally got around to doing some tests (https://forums.iboats.com/threads/97-50hp-3cyl-will-not-rev-past-3000.767953/)

Using a inductive timing light all cyl seem to be firing at idle, (couldn't test it on the lake as I'm by myself)
Spark gap test tool.
Top cyl OK, 1/2" gap good snapping spark
Mid cly no spark even closed the gap to about 1/4"
Bottom cyl OK, 1/2" gap good snapping spark

Tried the top coil-sparkplug lead on the middle and vise-versa and no change
Moved the primary wire from the middle cyl to the top coil and it has spark
Moved the primary wire from the top cyl to the middle coil and no spark

So I figure the coil is bad, took the coil off and brought it home.
Doing some checks with a DVM
Ground to primary post I get 0.3 ohms
Ground to secondary I get 338 ohms
Those seem to be inline with what specs I find online as being Okay

Can it ohm out Okay and still be faulty?

 

[Nordin]

Yes it can ohm out good but still be bad.
Remember that when you check the resistance with a VOM you only put out the battery voltage from the VOM, about 4.5, 6 och 9 Volts depending on brand of VOM.
The CDI box are putting 200+ Volt to the primery side of the coil.
I think you have a bad insulation inside the coil between the primery and secondary side of the coil.
The spark will jump inside the coil or even not jump at all.
Best way to check a coil is to use a coil tester that will put out 200+ Volt.

 

[bleb]

Thanks, that's along what I was figuring since there is no real load at all on the meter. If it ohmed bad it tells you there's a open or short condition but if it ohms good it's not really a true result.
I went with the results I got swapping leads around on the spark gap test and ordered a new coil online (none of the local places had any)
Fingers crossed it actually gets here when they claim
Thanks again

 

[Nordin]

Okey.
BTW: The prime side of the coil is a very low ohm winding.
The VOM will show very low resistance and you do not know if it is okey or it is a short circuit.
The measurement will show almost the same value.

 

[bleb]

That's sort of what I might be seeing, 0.3 ohms.
I received a new CDI coil today but unfortunately I wont get back up to the boat to try it until next weekend... Fingers crossed but I'm fairly certain this is the problem (or at least A problem) with how I swapped everything around to isolate this coil as a problem
Thanks again for the input guys

 

[ct1762@gmail.com]

That's sort of what I might be seeing, 0.3 ohms.
I received a new CDI coil today but unfortunately I wont get back up to the boat to try it until next weekend... Fingers crossed but I'm fairly certain this is the problem (or at least A problem) with how I swapped everything around to isolate this coil as a problem
Thanks again for the input guys

sounds like you got it sorted, but just thought i'd remind that SLOW ("limp overheat") mode kicks in around 2800 on that motor. not your issue im sure, but good idea to check head temp at idle. 125-152.5 degrees at 900rpm at top of head.

 

[bleb]

I'm getting a good stream from the pump but I'll bring my thermal gun up next weekend as well to double-triple check

 

[ct1762@gmail.com]

I'm getting a good stream from the pump but I'll bring my thermal gun up next weekend as well to double-triple check

yea always good practice. indicator stream means nothing , only pump is working. head temps are what matter here. cheers.

 

[bleb]

Swapped in the new coil and the thing is running like a top. Now the real question is do I pick up a spare coil or two or wait for one of the other no-name brand coils that they put in last year to quit....

 

[tphoyt]

Nothing wrong with having spare parts on hand and rest to go.

 

[racerone]

Install factory coils and you are good for many years.----They rarely fail.

 

[bleb]

I'm didn't even know the mechansic I used changed out the originals last year until this happened... (and I asked, he didn't keep any of the parts or at least thats what he said when I called the other week)
The new one I bought is a CDI which seems to be about as good as I can find right now.

 

[ct1762@gmail.com]

I'm didn't even know the mechansic I used changed out the originals last year until this happened... (and I asked, he didn't keep any of the parts or at least thats what he said when I called the other week)
The new one I bought is a CDI which seems to be about as good as I can find right now.

good price from an ebay seller for OEM 582508's.