Auto ignition coil -vs- marine coil output?

[watersarg]

Does anyone know if there is a difference in the output to the distributor of an automotive coil and a marine coil at WOT?

I recently purchased a boat with a 250L CID and noticed it had a new "Napa" coil installed. The boat runs well up to ~3500 RPM but at WOT ~4300 RPM it sounds like there's an ignition "knock". Not very bad like low octane fuel knock but a difinate pinging noise. Back the throttle down and it goes away. Was wondering if the coil was having trouble delivering the right voltage at that high RPM?

I'm planning to check compression, adjust valves a necessary then check the timing and dwell on the ignition but I'd like to rule out the coil as a possible cause sooner rather than later.

Thanks,

 

[Bondo]

Re: Auto ignition coil -vs- marine coil output?

Ayuh,... Sounds like it's goin' Lean,... Too Lean,... Check the fuel system...

 

[betayv]

Re: Auto ignition coil -vs- marine coil output?

I dont think is the coil but just to let you know NAPA make some coils that are for marine and industrial applications.

 

[180shabah]

Re: Auto ignition coil -vs- marine coil output?

old boat = old fuel system

Do you have a water seperator? When was it last replaced?
Is the fuel fresh?
How old are fuel filter/s?

 

[watersarg]

Re: Auto ignition coil -vs- marine coil output?

Water separator brand new, new 92 octane fuel with lead additive, new fuel pump and carberator filters.

I can check the part number of the installed coil to determine if it's marine or automotive.

Question still remains.... in general terms "Is there a difference in the output voltage between automotive and marine coils?" Since marine engines rev so high as opposed to automotive engines, does the ignition require a "hotter" coil?

 

[WizeOne]

Re: Auto ignition coil -vs- marine coil output?

...Question still remains.... in general terms "Is there a difference in the output voltage between automotive and marine coils?"....

In short, NO! Pull your plugs after a high rpm run and see what they look like.

 

[180shabah]

Re: Auto ignition coil -vs- marine coil output?

Ignition coils is just a sealed transformer - there is no difference between auto and marine. Make sure you match your coil to your type (electronic or points) of ignition though.

As for marine engines reving so high comoared to auto engines, actually it is quite the opposite. Most marine engines have a WOT spec somewhere between 4200 and 5000 RPM. It is not uncommon for an auto engine to have a redline in the 6000-6500 range. Boats do tend run sustained RPMs of 3-4000, but your ignition will have do problem keeping up with that all day long. You will see no benefit running a "hotter" coil.

 

[watersarg]

Re: Auto ignition coil -vs- marine coil output?

Solved the ignition problem. As the thread suggests it was not the coil after all. After doing the compression test (5 cylinders @151# & 1 @157# ) I turned to the ignition......the dwell on the points was ~6 degress low, the timing was so far advanced I had a hard time finding the timing mark with the light with the engine running. I had to bump the starter and paint the mark white to find it. Retarded the timing back to 6 BTDC, stuck the boat in the water and viola, no ignition knock.

 

[180shabah]

Re: Auto ignition coil -vs- marine coil output?

Easy fixes are always good.

 

[picklenjim]

Re: Auto ignition coil -vs- marine coil output?

Just telling you in case you didn't know always set the dwell first and then the timing.Changing the dwell will change your timing but changing your timing will not change your dwell.