Testing an ignition coil

[JDK]

Before I order a new coil from Don I'd like to test mine to verify its what's causing my issues, can you please tell me what the proper resistance ranges are for a good coil ? Thanks

[joe_db]

3-4 ohms would be good, but a low voltage resistance measurement is not always definitive. For one thing, the secondary could have issues that would not show up at all testing primary resistance. Why do you think you need a new coil?

[JOHN COOKSON]

Disconnect the existing wire from coil - and temporally replace it with a short length of wire that has the other end bared. Pull the big wire out of the center of the distributor. Turn the key on or otherwise power up the coil. Hold the big wire near ground (the engine). Scratch or touch the wire attached to coil - to ground. This simulates the points\EI opening and closing. If you see some sort of an arc the coil is working but perhaps weak.
Reattach the wire to the distributor at coil -. Hold the big wire from the center of the coil near ground while you crank the engine. A 1/2 to 3/4" blue white arc is good. Anything less the coil is a goner or the voltage at coil + is low.

TRUE GRIT

[ndutton]

I'll add or concur that primary resistance is a possible indicator but is far from conclusive. To really know the condition of the coil you need to confirm resistance at approx. 150°F as well as cold and the ability of the coil to deliver a hot, snapping, 25K volt (or more) blue spark that will jump an .035 gap 120 times a second. How you determine that I have no idea. It's much easier to simply replace the coil if it's suspect.

Now, what makes you think the coil is a problem? Has it been overheated? Performance problem? Intermittent shutdowns? Do you have points or electronic ignition?

[Al Schober]

A coil is a good spare to carry aboard - not expensive. If you have an ignition problem and the spare coil fixes it - well and good. Buy another spare. If the spare doesn't fix it, then you still have the spare.

[ndutton]

A spare ignition too. Most of us EI guys still carry the old points and condenser pre-adjusted on the original points plate.

[sastanley]

I will admit to being an old school guy and still carrying points and a condenser on its plate aboard, and also carry a spare EI unit + coil.

My friend Spencer with C-30 #355 (recently sold) has run with points just fine since he owned it for the last 4 years. The condenser did fail, but it was $7 I think. Two boats at the same dock with spares on hand help with troubleshooting.

Coils seem to work forever, or if they get fried, work for 45-60 minutes. Once one fails, I personally would discard it.

[Dave Neptune]

I ran my EI for 34 years and never a failure. I had an old Allison (a Crane unit) like the Indigo that I used until Indigo came up with another Crane model with the indicator lite. That lite was the only reason for the change and that was when I tried a resistor although I had had no coil failures. I tossed my points pak I had in the ditty box and put the old Allison unit in as a spare. All interchangeable even the plugs!

Dave Neptune

[JDK]

Sorry I still haven't responded, I haven't been out to my boat hardly but at this point I'm fairly sure I'm not even getting a fire out of it......the old man I work with at the shop tells me likely my distributor module , not the coil, is bad....any way to test ? He said if it was an old car that fucked up it would be exactly that, all day long.....as he's pretty smart when it comes to primitive cars I tend to believe him.....

[JOHN COOKSON]

it......the old man I work with at the shop tells me likely my distributor module , not the coil, is bad....any way to test ? comes to p.....

See post #3.

TRUE GRIT

[Peter Betulia]

Have spark!

Sorry for the very late response. My initial problem was no spark at the coil. I went back and carefully set the point gap with new points,using a new coil and got spark at the plugs. I sprayed a bit of staring fluid in the carb and the engine rumbled to life. I then hooked up a fuel supply (not boats tank) and started the motor. I opened the seacock and checked the exhaust....a decent amount of water and smoke which disappeared after a bit.
I had a gasket leak from the fitting that goes from the head to the manifold. When I removed the fitting I saw much black crud in the head. Decided to hook it all up and see if water would pass. Started motor and no water from the exhaust. Quickly shut it down and decided to acid flush the system. The PO had rigged a hose that allowed water to pass to the T valve at the sea cock. I mixed the solution but the pump would not draw the water from the bucket. I looked at the sea strainer (Always had a leak as the gasket is bad and one of the 3 threaded rods that hold the sight glass is missing)
I attached a hose to head side of motor and ran it to a bucket ...started motor and there was water flow to bucket. scince I could not get water to flow from bucket. I poured some of the solution through a funnel into the hose on the manifold side. Hooked everything up quickly and started engine up all while pouring fresh water in the hose that met the T fitting. Now exhaust and water flowed normaly. Sea strainer will be repaired or replaced. I want to do another flush. Could it's leaking be the reason water could not be drawn frow my fesh water bucket?
Anyway....very happy to have motor running. Hardly turns over one revolution before it catches ...very satisfying!