84 FJ60 Ignition coil resistance… don’t make em like they used to? (1 Viewer)

[Spino]

Hello. Recently I got the notion to check the primary and secondary resistance of the ignition coil on my 1984 FJ60. It was out of spec. So, I ordered a new one. But when I checked this new coil’s resistance, I found it too was not in spec. It’s an Intermotor coil… nothing fancy but surely it would do?

Primary spec: .5-.7 Ohms
Secondary spec: 11.5-15.5 kOhms

… the coil is reading 2.25 and 20, respectively.

Why would it be so far off? Are new coils somehow different than those from 40 years ago? Should I just put away the multimeter and not worry so much?

Thanks!

 

[1911]

Hello. Recently I got the notion to check the primary and secondary resistance of the ignition coil on my 1984 FJ60. It was out of spec. So, I ordered a new one. But when I checked this new coil’s resistance, I found it too was not in spec. It’s an Intermotor coil… nothing fancy but surely it would do?

Primary spec: .5-.7 Ohms
Secondary spec: 11.5-15.5 kOhms

… the coil is reading 2.25 and 20, respectively.

Why would it be so far off? Are new coils somehow different than those from 40 years ago? Should I just put away the multimeter and not worry so much?

Thanks!

My take (I'm not an electrical engineer, just an experienced mechanic): your new coil will probably work just fine, but it may not be as efficient as one that was perfectly in spec, i.e., it may generate a little more heat.

In my experience, most coil problems come from the secondary windings cracking from vibration or impact and making an intermittent open circuit which makes for an intermittent spark. Difficult to diagnose because it might read just fine in a static measurement in the shop/driveway when it's not moving.

Once in a blue moon I've seen an old coil that was corroded internally and had almost infinite resistance, but this is rare with modern plastic-case sealed coils.

If you're not having intermittent spark problems, your coil is probably good.

 

[Spino]

Thanks! After I posted I learned how the Ohms adjust dial works on my multimeter, and now I’ve solved my mystery… oops. RTFM.