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Old 31 October 2022, 20:51   #1
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Suzuki Ignition coil packs

After a little advice - I have an intermittent fault on my Suzuki DT65 (1998) outboard where by when it is warm and I throttle off it will miss fire, then idle fine. When I throttle up it sometimes cuts out. It always then starts on the key and it may take a few attempts to get through what ever the issue is and get the revs on. I have had the carbs cleaned, balanced, new fuel lines and pump so now going down the electrical route.

I tested the coil packs over the weekend and got the following resistance readings -

Top
Primary - 0.8 ohms
Sec - 11.75 ohms

Middle
Primary - 0.8 ohms
Sec - 11.37 ohms

Bottom
Primary - 0.8 ohms
Sec - 11.03

I have some photo copies of some data from the manual, and if I have the right one the limits are

Primary - 0.1 to 0.3 ohms
Sec - 10.0 to 15.0 ohms

Seems hard to believe that all three coils are out of limits and that I'm getting a consistent 0.8 ohms for them all? Appreciate that the info im giving is limited but any advice would be appreciated.

Withers!
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Old 01 November 2022, 00:09   #2
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Coil issues tend to show themselves under load causing a misfire. With the fact they are all similar I would go back to fuel issues. Often the factory specs for coils seems to deviate from reality too.

Might just need the mixture adjusted. Sounds like it could be rich coming back to idle. There are tells for whether it is rich or lean.

If it continues remove and clean the carbs with high pressure air and carb cleaner, then readjust mixture and idle screws.
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Old 01 November 2022, 12:17   #3
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I have no experience of this engine type but from decades of engine experience...

I too would think those coils are OK on static readings given their even results. However that doesn't say they are all OK when heat soaked/under load. I had an infuriating issue with an old days car once which was finally diagnosed by running leads from the coil to a test meter in the car and getting some in-running readings where at the point of misfire it could be seen the coil readings were going wildly out of spec. Not quite so easy with an OB on the water and three coils though.

Re carb cleaning... on many occasions over decades I've found however careful you think you've been you don't always get them totally sorted 100% first time. So like Peter I'd not discount revisiting a carb clean.
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Old 04 November 2022, 08:41   #4
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Quote:
Originally Posted by Peter_C View Post
Coil issues tend to show themselves under load causing a misfire. With the fact they are all similar I would go back to fuel issues. Often the factory specs for coils seems to deviate from reality too.

Might just need the mixture adjusted. Sounds like it could be rich coming back to idle. There are tells for whether it is rich or lean.

If it continues remove and clean the carbs with high pressure air and carb cleaner, then readjust mixture and idle screws.
Thanks Peter - The fuel system is 100% new and the carbs have been cleaned, balanced by an outboard specialist (he is not an electrical specialist but understands the basics) Think as you suggest I may look at the mixture (maybe with the guy who services the engine with me) and test the coil packs when they are in use.
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Old 04 November 2022, 08:43   #5
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Quote:
Originally Posted by Fenlander View Post
I have no experience of this engine type but from decades of engine experience...

I too would think those coils are OK on static readings given their even results. However that doesn't say they are all OK when heat soaked/under load. I had an infuriating issue with an old days car once which was finally diagnosed by running leads from the coil to a test meter in the car and getting some in-running readings where at the point of misfire it could be seen the coil readings were going wildly out of spec. Not quite so easy with an OB on the water and three coils though.

Re carb cleaning... on many occasions over decades I've found however careful you think you've been you don't always get them totally sorted 100% first time. So like Peter I'd not discount revisiting a carb clean.

Thanks for the response - I like the idea of being able to test the coils in use (inline test capability) I may have a play with that concept :-)
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Old 05 November 2022, 18:02   #6
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Quote:
Originally Posted by Withers79 View Post
After a little advice - I have an intermittent fault on my Suzuki DT65 (1998) outboard where by when it is warm and I throttle off it will miss fire, then idle fine. When I throttle up it sometimes cuts out. It always then starts on the key and it may take a few attempts to get through what ever the issue is and get the revs on. I have had the carbs cleaned, balanced, new fuel lines and pump so now going down the electrical route.

I tested the coil packs over the weekend and got the following resistance readings -

Top
Primary - 0.8 ohms
Sec - 11.75 ohms

Middle
Primary - 0.8 ohms
Sec - 11.37 ohms

Bottom
Primary - 0.8 ohms
Sec - 11.03

I have some photo copies of some data from the manual, and if I have the right one the limits are

Primary - 0.1 to 0.3 ohms
Sec - 10.0 to 15.0 ohms

Seems hard to believe that all three coils are out of limits and that I'm getting a consistent 0.8 ohms for them all? Appreciate that the info im giving is limited but any advice would be appreciated.

Withers!
Even a very expensive high impedance multimeter will struggle to read less than one ohm accurately.

TBH those readings look fine, however, your problem is more likely to be the coil insulation breaking down and causing tracking.

The only real answer is to get a known good coil pack to try on each cylinder, or work out which cylinder is missing and move the coil packs around to see if the fault moves with the change..

My first action would be the change the plugs.
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Old 07 November 2022, 08:49   #7
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There is another way to spot a coil tracking to earth - run the engine in the dark and look carefully around the coils for sparks
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Old 25 November 2022, 21:32   #8
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Hi Withers
Me dt 65 has got the same problem as yours and everything checks out fine. Did you get the bottom of your problem.
Cheers Kevin
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