Coil Testing

[Johnny340]

I'm trying to test my coil and spark plug wires and get nothing when I connect the meter leads to each spark plug wire simultaneously. I assume this measures the resistance of the secondary windings in the coil as well as the spark plug wires. Anyway, I get nothing. Is there a break in the wire? Am I hooking up the tester right? Thanks.

Here's the part of the tech faq I'm trying to follow:

4. Ignition coil. Not many folks do not have a meter capable of resolving the almost dead short of the primary on this coil. But if you do, the resistance should be .078 to .106 DON'T forget to subtract the meter leads resistance by shorting together and subtracting, or adjusting the zero ohms pot, if you have it. Also, remove and insert the leads in the sockets to clean the connection.....I often see 1 ohm or more go down to .2 or .3 by performing this task.
NEXT, check the health of your spark plug wires, or high tension wires as the Brits like to say. The only way to test them properly is to remove the boots and get to the end of the wire. You can try jamming the point of the meter probes into the end, but due to the dirt and metal dust, it often does NOT give a solid connection / reading. If you have electrical contact cleaner, by all means spray with that first. You should read 3500 to 4700 ohms, or 3.5 to 4.7K ohms STEADY....while flexing the wires from end to end. If you get any fluctuations, they are bad...IE breaking up inside, turning to a high resistance powder of metal and rubber. I have seen bad plug wires cause problems with idle and low speed only, mid range only, and high speed only, and every combination thereof. Very strange !!!

I assume the 'primary' refers to the small wires going into the coil.

 

[Pro-pulsion]

If you can remove the leads from the coil and test the posts inside the coil then I would do that first. If you have to test the secondary windings with the plug leads attached then set your meter to it's lowest resistance setting first and try that. Never start on any setting higher than the lowest when testing electrical/electronic components. If there is a resistance sensitive diode or other component somewhere in there and you start on a higher setting you could blow that component from trying to force too much through it. If you get no reading from the lowest setting keep progressing up the dial until you get a reading. As it seems right now, your meter might not be picking up anything because it's either set too high or too low. If you want to test the primary windings zero out your meter, put one test lead onto one small wire and one on the laminated core. The general rule of thumb with small engine coil windings or switches is that there should not be higher then 0.3 ohms of resistance.

Just curious but why are you testing your coil leads? Is there no spark? The best way to test is with an actual testing plug. They look like a spark plug but have a spring loaded clip to clip it on the head studs and no bridge over the porcelain. The gap is massive so if your coil can jump that gap then the coil (when cold at least) and leads are good. They're really inexpensive to buy too...somewhere around 15 bucks and you can get them just about anywhere.

 

[Johnny340]

Just curious but why are you testing your coil leads?

Sometimes I get no spark on the rear cylinder. I suspect bad plug wires because when I put new boots on, the wire was broken off inside so there could be other breaks.

I'm still not 100% on where to put the test leads. I was putting them both on the end of the plug wires starting with the lowest ohm setting and got no reading. I don't think the wires are removable from the coil.

 

[Pro-pulsion]

No there not removable. I can see they're sealed in to the coil. Have you tried pulling the plugs and reversing the wires when this condition happens to see if it's one lead or the other? It could be further in the coil too. If it seems to only do this when it's hot then the coil may be breaking down under load.

 

[Pro-pulsion]

Oh yeah, see your orange and black leads with the white connectors? Those are the leads for the primary winding. Unplug them, zero out your meter and stick a test lead in one of those plugs. Then touch the other lead on a ground. I don't know why but I was thinking that coil had a laminated core. Actually after opening my eyes lol I see the core now, it's just coated...touch a test lead to the mounting screw for the coil and one in one of the connectors. You should get a reading there.

Another question...is that tape wrapped around the leads or are they weather cracked?

 

[Johnny340]

OK, but can't I check the plug wires somehow?
Yea, that's just tape around them.

It is the rear lead that fails when it happens. I can tell from the spark plug.

 

[Johnny340]

OK, I'm not an idiot after all. Yes, to test the wires just hook each end of the test leads to both plug wire ends. The resistance should be 3.5 - 4.7 K ohms. I had no reading because one of my plug wires had a break in it. The engine would run because the spark would jump this break. Intermittently.

I cut the wire back past the break and put the boot back on. It's a little short and who knows where it will break next so a new coil is on order.

 

[Idok]

i replaced a coil this weekend on a 61x setup....

if you spark checked, both cyls would show a nice clean spark....


when started the front cyl would rev right up but nothing on the rear.......plug wires are broken inside

replaced and ran good as new!

 

[Pro-pulsion]

Glad to hear you found the fault :bump: