2005 Ford Thunderbird - coils

What is with the coils on top of each cylinder and why do they all fail at once?

Individual coils perform better than one. Bigger spark, more consistent and with individual coils, you don’t need a distributor.

And they don’t fail all at once unless something makes them fail or your mechanic has a boat payment coming up.

It would stand to reason that they all have the same engineered service life, and they were all installed at the same time.

Putting the coils on top of the spark plugs gives you less parts to fail than mounting them remotely and running a wire to the spark plug.

I have a bathroom light fixture with 8 light bulbs. I installed all new bulbs when I put it in. When one bulb burns out, another one follows shortly, then another. They’re all the same age and get the same use. Stands to reason they all have a similar lifespan. Same thing with your coils.

Distributing the coils like that helps reduce the heat load they need to be designed to handle, as each one is called on to produce fewer sparks per mile compared to a single coil. But if the manufacturer downsizes them to compensate, they might not last any longer than a single coil, or even be less robust. If your coils are burning out all the time, might not be a coil configuration problem but a manufacturer design problem. One other thing to consider, the coil on plug configuration comes with electronic ignition systems. Those system will increase the power to the coil as the spark plug gap widens, as it does with miles driven. The upside of that is the engine continues to run well even if the plug gap is wider than spec; the downside is it burns out the coils faster. To keep your coils working longer be sure to replace the plugs per the manufacturer’s time interval, and replacing them more often than that will only help, not hurt, the coil life.