Ignition Coil Removal and Testing

This is the ignition coil for a 1986 Ford Bronco (and probably lots of other early EFI Fords with a 5.0L V8. When my Bronco wouldn't start anymore, after checking the fuel pump and fuel pressure, this was the next thing to test.



This information will (hopefully) help anyone who has a need to test their ignition coil.

When you open the hood of your Bronco/F150/F250/etc, you should see something similar to this:


(I've already removed the air cleaner and intake hoses from the manifold, so yours should be slightly different. You've pretty much got to take them off before you do much of anything on these motors. You can remove the intake hoses with a standard ["flat-head"] screwdriver, and the air cleaner will come off with a small socket, 1/8" or 3/16" -ish)

See that part right in the middle of the photo? That's the A/C compressor. If your vehicle has A/C, you'll have one of these. Unless you've got monkey arms and girl hands, it will need to come off. Mine had 5 or 6 bolts, some 9/16" and some 5/8" - just unbolt them and lift (it's heavy) the compressor free of the mounting brackets. Do NOT remove the hoses from the compressor. It's unnecessary and you'll have to re-do the entire A/C system with new Freon. Just set the compressor on top of the intake manifold, out of the way. The hoses are flexible enough.

Once you've removed the A/C compressor and placed it out of the way, things will look like this:


Now, focus in on the ignition coil. To remove it, you'll need a very small socket, or a crescent wrench. There are four small bolts on each corner of the coil. Remove them, then don't forget to unplug the wire coupling, and pull off the coil assembly.


Now, you'll be left with the coil, and you'll need to bench test it. To do so, you'll need an ohmmeter, or a multimeter that can measure ohms. You'll want to test the resistance between the two small contacts on the side to measure the primary winding resistance. Look up the exact specifications in the service manual for your vehicle. If the coil tests even a little off, it should be replaced. Next, test the resistance between the outer 12v contact and the center post (the center post is the one that looks like a spark plug). If the secondary winding is out of spec compared to your service manual, replace the ignition coil.

A new ignition coil (obviously) depends on the vehicle and engine, but for reference, one for my Bronco would have cost only $17.99, so if you're in doubt, just replace it.