Could wrong ignition coil hurt???

What's the difference between a Sierra Ignition coil part# 18-5437 and part# 18-5433 ? I have twin 1990 OMC 5.7L Cobra's in my FourWinns 315 Vista, and one week ago my port engine would not start after running great this summer and the past 8 yrs. The starboard engine ran great. So I tried the usual replacements including dist cap, rotor, spark plugs and checked much of the wiring, connectors, wire terminals, etc. So I swapped the ignition coil from the starboard engine and it worked good and started the port engine. So I bought two new ignition coils part# 18-5433 because I think they were the original coils and figured if one was bad I might as well replace them both. I trusted the parts counter person sold me the correct parts. So now both engines ran great....for about 15 minutes.....about 10 minutes to idle out the river, and 5 mins on plane going apx 30mph at apx3500rpm...then I slowly lost engine power over apx 1-2minutes untill I could no longer run the engines above 1000rpms because it would cough and sputter... So now after some WEB research it looks like they sold me the WRONG IGNITION COILS....I believe I need the part# 18-5437 coil. So I want to know what is the difference between the two coils? And could using the wrong coils for 15 minutes have now caused my engines to run terrible? They seem to idle ok, but spit and sputter when I give throttle and are worse when under way and pushing the boat and terrible when I try to get on plane. What could the wrong coils have damaged on both engines to react the exact same way? I don't think some other unrelated failure is occurring (ie: water in gas) ....that would be too much of a coincidence. Any help would be greatly appreciated.

On a 1990 5.7 OMC they use a resistor type coil. There is a resistor in the wiring harness to take the voltage down to around 9 volts. It might have burned out the points.

kimcrwbr1 said:

Both of those coils are externally resisted for a points system if your distributors has the electronic pickup I agree you need to use internally resisted coils.

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I see the boat was updated to the electronic ignition sensor under the rotor (in place of the points and condenser)...and the old coils I took off have words stampe on the "Use with external resistor"...so that is what I bought. Are you saying I should coils with INTERNL resistors?
I am rally wondering if installing the correct coils will fix my problem???
Or did those wrong coils mess up something else??
Thank you

You could also replace your 24 year old systems, and go with new systems.
For these engines, since you likely have two standard LH rotation engines, I'd recommend the Mallory YLM 624 AV.
The YLM uses VR technology, and maintains the mechanical advance.

The Delco Voyager would be another suggestion.


Anything but the Pertronix Hall Effect units.


.

BarryJay said:

I see the boat was updated to the electronic ignition sensor under the rotor (in place of the points and condenser)...and the old coils I took off have words stampe on the "Use with external resistor"...so that is what I bought. Are you saying I should coils with INTERNL resistors?
I am rally wondering if installing the correct coils will fix my problem???
Or did those wrong coils mess up something else??
Thank you

Click to expand...

the answer requires more info. You'll need to see how the coils are supplied power. If the original wire was not disrupted, it is a resistor wire built into the harness and the original spec coil can be used. If that was bypassed during the electronic conversion, then the coil requirement changes.

Put the red lead of your voltmeter on the coil + post, put the negative lead on battery negative (NOT coil negative!!!!) and see what voltage ya got with the key on.

If it's 12V, you need a coil that runs on 12V. If it's between 8.5 and 10.5V, you need a coil designed for an external resistor.

Tractor Supply Company is where I generally go for coils. They have those two choices for 12V coils on the shelf and they fit right in the bracket where the OMC one was.

Good info hystat! But, may I suggest that you can use any good ground such as the engine block when using the voltmeter, if the wires don't reach the Neg. battery terminal.

By the way, So, Tractor supply has good generic 12Volt coils, thanks for the tip!