1993 larson 4.3 coil

[Jakem]

A friend has asked me to find out what ignition coil he needs ohm wise. From what says it's canister style...any suggestions

 

[dubs283]

No idea what the ohms spec is but based on the vintage and is a 4.3 if everything is stock mercruiser for the ignition system it's most likely a thunderbolt. Only one style coil available for that system

Out of curiosity why is the coil being replaced?

 

[Jakem]

He says it's all corroded and sputters...I suppose someone told him coil

 

[achris]

 

[dubs283]

He says it's all corroded and sputters...I suppose someone told him coil

Possible the coil is the culprit for a sputtering engine. Not highly likely though. There are many other parts that fail long before a coil causes issues

 

[Scott06]

He says it's all corroded and sputters...I suppose someone told him coil

Lots of things it could be. He can ohm out the coil vs specs chris gives. If its bad replace it.
would start with checking contents if fuel filter for anything but fresh clean gas.
verify the condition of ignition components
prob needs a carb rebuild

 

[Drcoffee]

I went to replace my coil. Bought a pertronix 45011 from amazon. Supposedly has 0.6 ohm. I Tested it when it arrived, and spec’d out at 1.5 ohm. Its getting returned. Whatever you buy, test it before installing it.

 

[achris]

I went to replace my coil. Bought a pertronix 45011 from amazon. Supposedly has 0.6 ohm. I Tested it when it arrived, and spec’d out at 1.5 ohm. Its getting returned. Whatever you buy, test it before installing it.

How did you test it? Straight multimeter ohms reading? Very low resistances like that are notoriously difficult to accurately measure with a multimeter..

Chris....

 

[Drcoffee]

How did you test it? Straight multimeter ohms reading? Very low resistances like that are notoriously difficult to accurately measure with a multimeter..

Chris....

Hi Chris, I pulled my old coil out and tested it. Same as pertronix. 1.4 ohm and 10,040 secondary. So I went ahead and installed it. I trashed the coil wire in the process. It was so corroded into the coil and I broke the wire. Ugh.

why doesnt the multi meter read it correctly?

 

[Scott06]

Hi Chris, I pulled my old coil out and tested it. Same as pertronix. 1.4 ohm and 10,040 secondary. So I went ahead and installed it. I trashed the coil wire in the process. It was so corroded into the coil and I broke the wire. Ugh.

why doesnt the multi meter read it correctly?

The coil wire is probably the issue.… ill let chris answer but i think the .6-.8 ohm is beyond the accuracy of the typical low buck multi meter.

 

[achris]

.... i think the .6-.8 ohm is beyond the accuracy of the typical low buck multi meter.

This... A multimeter uses current (voltage drop across the unknown resistance vs a high tolerance known resistance in series), but the voltage the meter can apply is limited, so the current drop in the internal known resistance will be very close to the 'short circuit' current, making the differentiation between a short and the very low resistances is too close to be accurate (can be as high as 1 ohm out)...

Best way to measure very low resistances is with a Wheatstone bridge...

Chris...

 

[Drcoffee]

That makes sense. BTW The tower on the old coil looked burned from arcing. Probably a good time to replace the original coil anyway. at times the engine would struggle to fire up when hot. I associated it with fuel vapor lock, could have been a weak spark too.