Ignition coil question

[jschmuch]

Ok, I just bought a boat that is turning into more of a project boat than I thought it would be. Its a 72 18' SeaRay with a Mercruiser 165 L6, serial number 2771484-5813433.

Anyway, I wanted to make sure that I'm testing the coil right. The volt meter is showing 3v when I put the leads on the +/- posts and the key is turned on but when I move the + to the center post its only from 0 - .3.

Its got a new battery, I already changed the plugs and alot of other stuff but I'm getting weak spark and don't really want to keep throwing any more parts at it.

Any help is much appreciated.

 

[Bifflefan]

Re: Ignition coil question

Anyway, I wanted to make sure that I'm testing the coil right. The volt meter is showing 3v when I put the leads on the +/- posts and the key is turned on but when I move the + to the center post its only from 0 - .3.

Nope.

You check the coil with OHM's not volts.
I dont recall the exact procedure right now, but yours is incorrect.

The voltage at the + term should 9v with the key on and 12v when cranking, checked with the red lead on the + term and the black on a ground not the - term.

The points may need adjusted adn or replaced. Bad wires, cap, rotor.
What is your dwell reading?

 

[wire2]

Re: Ignition coil question

That vintage will have points in the distributer, and it makes a huge difference to the voltage on the + and - coil terminals whether the points are open or closed.
If closed, you should read ~9v b/c the coil - is in series with a resistor.
If open, it will read very low, b/c the - lead has only the condenser connected to it.
One exception, if the coil has a built in resistor, the reading should be slightly less than battery voltage

 

[Bifflefan]

Re: Ignition coil question

If closed, you should read ~9v b/c the coil - is in series with a resistor.
If open, it will read very low, b/c the - lead has only the condenser connected to it.
One exception, if the coil has a built in resistor, the reading should be slightly less than battery voltage

Wrong.

The 9v is the voltage coming from the wire to the coil and is not affected by the points at all.

 

[jschmuch]

Re: Ignition coil question

The dwell readings 31? and the points are clean and I was testing it with the dist disconnected. If anyone can point me in the right direction on testing it that would be great, otherwise I'll just spend $30 more and see if that fixes it

 

[jschmuch]

Re: Ignition coil question

Or if anyone has a cross reference for the coil that would work because I don't really want to wait for shipping and I've been unable to find any numbers other than Merc and Sierra.

 

[Bifflefan]

Re: Ignition coil question

http://autorepair.about.com/od/troubleshooting/ss/coil-test-ohm.htm

http://wiki.answers.com/Q/How_do_you_test_an_ignition_coil

here is a couple

 

[jschmuch]

Re: Ignition coil question

Well, I did the resistance tests from your links and am showing 1.3 for the primary and 13.03 for the secondary winding. I wasn't able to find the specs in the manual so it doesnt really help but since you guys are saying I should have 9V to the wire it sounds like I need to be looking for a ground or open somewhere anyway.

 

[wire2]

Re: Ignition coil question

Wrong.

The 9v is the voltage coming from the wire to the coil and is not affected by the points at all.

That 9v is in reference to engine ground and is constant, yes.

But the OP was asking what reading to expect on the coil terminals;
"The volt meter is showing 3v when I put the leads on the +/- posts and the key is turned on"

I alluded to the same connections in my response;
"it makes a huge difference to the voltage on the + and - coil terminals whether the points are open or closed. "

 

[rodbolt]

Re: Ignition coil question

points open,key on engine off, you should see about battery voltage from the coil + to the engine block.
resistors wont work unless the circuit is active and with the points open its not active.
points closed key on engine off you should see less than about 3V to 0 V.
your now measureing the potential difference between the coil + to the coil neg(coil windings will drop some voltage) through the points and the point ground plate to engine ground.
its a very simple DC circuit and the points are simply an on off switch yet folks still get confused.
voltage is a simple measurement of electrical pressure in a circuit, voltage DOES NOT flow.
kinda like your garden hose, kink the hose in the middle with full pressure,the kink is the equivalent of a resistor.
squeeze the spray nozzle.
you will note at first pressure at the nozzle is normal,voltage, but rapidly the pressure and flow drop, current flows.
close the spray nozzle and you wil notice hose pressure builds back to normal even with a restriction.
restriction is only noticed when the hose nozzle is active.

 

[jschmuch]

Re: Ignition coil question

I know my OP was probably confusing but I had the dist disconnected and the wires from the harness connected on the first test so basically I was just testing the volts going to the coil. Would that give a proper reading or do I need to just have the + lead on the + wire and the - on a ground?

Sorry, I'm really new to all this and just know a little from reading the past few days.

 

[wire2]

Re: Ignition coil question

I know my OP was probably confusing but I had the dist disconnected and the wires from the harness connected on the first test so basically I was just testing the volts going to the coil. Would that give a proper reading or do I need to just have the + lead on the + wire and the - on a ground?

Sorry, I'm really new to all this and just know a little from reading the past few days.

Very simply;
with key on and points closed, you should read ~9v between the + coil terminal and engine ground.
The coil - terminal is grounded to the engine ONLY WHEN the points are closed.
When points are open, there's no current, so you'll read ~battery voltage on the both + and - terminals in reference to engine ground.

 

[jschmuch]

Re: Ignition coil question

Thanks guys, after all the testing everything seems to be pointing to the dist/plug wires. I already changed the carb, cleaned the fuel lines, tested the fuel pump and put a new fuel filter on so I know its not a fuel problem. Also cleaned and set the points and everything on the other side of the dist is testing good so I'm just going to go ahead and buy the dist/plug wires.

The cap on the one thats on there looks like some cheapo automotive one "says standardPlus on it" that the old owner must have put in anyway so I'd probably just be better off buying the right one anyway.

 

[wire2]

Re: Ignition coil question

If you pull the wire out of the center terminal of the distributor, (leave the coil end alone), bring the dist. end to within 1/8" of the engine, then crank the engine, you should see a series of sparks.
You should also see a spark with the coil wire like that if you pull the distributer cap, key on, with points closed, then open the points with your fingernail. There will be a slight arc between the points on opening if it's working normally.

Plug wires should read ~1000 ohms per inch of length. The resistance doesn't affect the spark to speak of, it's very high voltage, so very low current.
And it stops the hi voltage from wiping out all radio signals within 150ft.

 

[Vincentgould]

Re: Ignition coil question

PLEASE HELP!
Ok, I smoked my coil and electronic ignition last summer and replaced them. The boat runs but the coil overheats after runningfor a long period on a hit day. Can someone tell me how the three wires are supposed to be connected to the coil? I habethe black going to the - and the purple going to the + and the grey is connected to the - my boat is a 1992 omc 5.0. Ford. Carburated but no points.