How to test an ignition coil?

[wvmedic]

I have tested a known bad coil using 20K ohms to test it + probe to plug wire ? probe to the two wires on the coil, I get 2.02 on both leads.

I did the same test on two new coils with the same results; I then test the known good coil and get a zero reading on the same test.

You ask how I know the one coil is good, well while the motor is running I pull one plug wire at a time. With the good coil running the bottom cylinder the motor stalls when I pull that plug wire, old and both new coils on top cylinder no change when I pull the plug wire.

Ok so I switch coils known good coil to top cylinder, new coils to bottom cylinder. I then pull the top plug wire motor stalls; fires the motor back up then pull the bottom plug wire no changes.

1973 50 HP Evinrude.

Any ideas?

Thanks Jeff.

 

[Vic.S]

Re: How to test an ignition coil?

What you have done swapping the coils indicates that you have one good coil and three bad ones!

 

[wvmedic]

Re: How to test an ignition coil?

Yes that is what I am thinking, but man getting two bad new coils from the same place.

I wouldn?t think that to be likely, that is why I was wondering about testing them to make sure.

Jeff.

 

[72SideWinderSS]

Re: How to test an ignition coil?

Check the resistance between the Plug lead and ground on the good coil, make a note, then check the resistance on the primary to ground on the good coil, make a note, then check resistance between the the Plug wire and the primary wire with the ground disconnected (Should be infinity).

Now compare with the bad coils.

 

[ezeke]

Re: How to test an ignition coil?

Pulling spark plug wires on a running CD ignition is a really good way to kill a powerpack; hope that's not what you have.

 

[wilde1j]

Re: How to test an ignition coil?

Test by taking the coils to a shop to have tested. My Dad's shop had a Merc-O-Tronic tester for coils and condensors. Easy. if you need a new one you'll be in the right place.

 

[wvmedic]

Re: How to test an ignition coil?

72SideWinderSS, I checked that as you stated and on the good coil I get a
0's on both tests. For the new coil I get 2.02 on both tests. That is testing with the multimeter on 20k ohms.


ezeke, didn't know that but no harm to the power pac. I replaced it with a new one, and the problem follows the new coils and the old coil as well.

Thanks Jeff.

 

[72SideWinderSS]

Re: How to test an ignition coil?

72SideWinderSS, I checked that as you stated and on the good coil I get a
0's on both tests. For the new coil I get 2.02 on both tests. That is testing with the multimeter on 20k ohms.


ezeke, didn't know that but no harm to the power pac. I replaced it with a new one, and the problem follows the new coils and the old coil as well.

Thanks Jeff.

You need to set your meter to read just ohms not 20k ohms.

Primary to ground approx. .3 ohms
Secondary to ground approx. 240 ohms

Primary to secondary approx. 240.3

I forgot that the primary and secondary share a common ground, thus the reading will be the sum of the individual readings.

You might find this good reading, click on trouble shooting.
http://www.rapair.com/Downloads/tabid/55/language/en-US/Default.aspx

Hope this helps.

 

[wvmedic]

Re: How to test an ignition coil?

72SideWinderSS, thanks I will check the ohms. I am also going to get a DVA meter and check the stator and timer base. I have read that trouble shooting from rapair but it doesn't really describe my problem.

I also don't under stand why the problem follows the coil if the coil isn't bad.

I am not sure what exactly the stator and the timer base dose, but I understand that both go to the power pac, and the power pac feeds the coils. There are two polls on the power pac that supply power to the coils, one for the top coil and one for the bottom coil. If the top coil is not firing and the bottom coil is, there could be an issue from what ever feeds power to that poll or a faulty power pac. But when I switch coils and put the previously firing coil on that poll and it continues to fire, that leads me to believe that there is nothing wrong with the power coming from that poll.

Is this correct thinking or am I way out in left field?

Thanks Jeff.

 

[72SideWinderSS]

Re: How to test an ignition coil?

Fourth Paragraph first:

In my opinion, you are thinking correctly.

You have just diagnosed a faulty coil.

In a nut shell, the stator is an alternator.
When the motor is spinning the magnets in the fly-wheel rim are passing by the stator, producing around 250 to 300 VAC. This voltage is used to charge up a condenser in the power-pac.

The timer base is a movable sensor with a coil or coils in it. When magnets in the hub of the fly-wheel pass by, it produces a very low voltage in the range of .5 to 1.5 volts, this voltage is what triggers the power-pac releasing the charge on the condenser to the coil, thus firing the spark plug.

I hope this helps.

 

[Vic.S]

Re: How to test an ignition coil?

The trouble with testing ignition coils with a multimeter on resistance ranges is that it wont detect shorted turns or bad insulation. It is useful only to check primary and secondary windings for continuity or shorting of a large proportion of the winding perhaps.

 

[ssavluk]

Re: How to test an ignition coil?

I am new to this sight and can't seem to "navigate" it very well. I have a 2 stroke Evinrude engine circa 1997 I inherited. I was told there is a governor on these engines that retards performance and that if it is removed will increase HP significantly. Is this true and how can this be done?

 

[Vic.S]

Re: How to test an ignition coil?

Sslavluk

Obviously having trouble with the site.


Go back to the index page http://forums.iboats.com/forumdisplay.php?f=24

near the top you will see a box "create new post"

Click that, put in a meaningful title so that people know what it is going to be about, type your question, then preview/submit it

Then you'll get your own thread that people can reply to.


BUT tellus exactly what engine you are talking about. HP, year and/or model number

 

[wvmedic]

Re: How to test an ignition coil?

Hey Vic.S, thanks for the info. You still think I'm right about it being a bad coil?

Jeff.

 

[72SideWinderSS]

Re: How to test an ignition coil?

Have you checked your plug wires & Plugs ?

The sure fire way to properly diagnose this issue is to preform the tests outlined in the trouble shooting guide using a peak reading DVA.

If you have the correct voltage range on the Orange wire coming from the power-pac, and the coil still will not fire, then either the ground is bad, the coil is bad, the plug wire is bad, or the plug is bad.

With the coil mounted on the motor, Disconnect the Orange wire on the suspect coil, Place the black lead of the DVM on a bare spot on the block or head, place the red lead on the primary lead of the coil, read the meter. You should read close to .3 ohm, if it is significantly higher you have a bad ground.
Do the same on the Secondary side of the coil, it should be similar.

If the Coil is grounding well, then check the continuity of the Plug wire.

If that checks out move on to the plug.
All you can do for the plug is to replace it with a new one, or one that is known to fire.

Good luck

 

[wvmedic]

Re: How to test an ignition coil?

72SideWinderSS, thanks again for replying. I didn?t see you?re other post #10, sorry.

Let me give a little more back ground, I?m sorry for not including it before but I just didn?t think about it.

The problem developed after I put the motor down for the winter, I was winterizing the motor stabil in the gas, fogging the cylinders and then the carbs. While I was fogging the carbs the motor didn?t seem to want to run right, so I just left it alone till this spring.

This spring I went to get it ready for the water, it was hard to start and would only run with the high idle set. So I was thinking possibly a carb issue, idle jets might be dirty so I took both carbs apart and cleaned them including blowing them out with my air compressor. After putting them back on the motor I was still having the same problem, so I check the spark and all seems well good blue spark at 7/16 +. Well I surmise that it still has to be a fuel problem, I pump the bulb while running and no change. So ok I must not have got the carbs as clean as I thought, of to the parts store for rebuild kits although I just rebuilt them before the last trip on the water before winterizing it.

Ok soaked the carbs blew them out, new kits in both adjust the floats per manual and still no go same problem.

Ok so now I check the fire again, this time I realize that one coil has intermittent fire the other is firing great. I switch wires on the power pack and now both coils have intermittent fire, I conclude that the power pack is faulty and buy a new one. Ok new power pack on still have the same problem, back to spark check and only have intermittent spark on one coil. So I switch coils around this time, problem follows the coil. I surmise that coil is bad plus it is leaking a sticky purple stuff from the back where there is a crack. I also thought as the problem followed the coil and the plugs are fairly new that the plugs aren?t the problem.

Ok so I think that I have it figured out and get a new coil, no luck still have a problem with the same cylinder. So I now check the firing good blue spark 7/16 + but still have an intermittent fire on that cylinder, ok so I move coils again and again the problem follows the coil. I get another new coil from the same place put it on, and again same problem.

Motor has a new rectifier, power pack, coil, starter and regulator.

I have taken the flywheel of and visually inspected the stator and trigger coils, they look good no obvious problems externally like being burnt or melting.

Sorry for such a winded post, but this thing is driving me crazy, albeit a short trip.

I am going to get a DVA meter next week.

Jeff.

 

[wvmedic]

Re: How to test an ignition coil?

I did do a link and sync as well, forgot to mention that.

Compression is 120# top and 115-118# on the bottom.

Jeff.

 

[72SideWinderSS]

Re: How to test an ignition coil?

Thanx for the details.

This sheds more light on the issue at hand.

I assumed (there I go again assuming) this was not an intermittent issue, but a total failure to create spark.

I would certainly remove every connection, especially the ground connections on the ignition system, clean the terminals and the block surface (bare metal) where they connect, coat them with a little dielectric grease and tighten them back up. As you know intermittent issues are difficult at best to track down.

Good compression by the way.

If you are going to purchase a DVM, might I suggest Stevens Instruments, good Products, good People, good Price.
http://www.stevensinstrument.com/

Please keep me posted Jeff.

good luck

 

[wvmedic]

Re: How to test an ignition coil?

72SideWinderSS, the wife cleaned every wire on the motor yesterday evening. She scraped them with a knife to shiny bare metal, she did the mounting surface as well and the problem is still present.

The wife is sick at the moment, so if she is feeling better later I will check the resistance on the coils again. Should be 0.2-1.0 primary's and 200-400 for the secondaries.

Jeff.

 

[Fl_Richard]

Re: How to test an ignition coil?

WHAT A GOOD WIFE!! God bless her hope she feels better soon!