Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Coils keep going bad

Our '99 Ford F250 V8, 250,000 miles was running very rough, they changed the plugs and 1 coil pack, 70 miles later it was running rough again, they changed another coil pack, 70 miles later it was running rough again, another coil pack. It is running well now, but it’s only 15 miles. will this keep happening until all 8 coils are replaced, or is something else causing them to go bad?

Is it exactly the same coil on the same cylinder going bad, or is it a different cylinder each time? If its a different cylinder, then you have learned that the coils are now all at the end of their usable lifespan, and you really should just replace them all at this point.

If its the same cylinder requiring replacement each time, then that cylinder has an issue, and you need to have the truck looked at by a mechanic.


It is different cylinders each time. why do they go bad at the same amount of miles each time, shouldn’t it be more random?

Your coils have 250k miles on them.
They were all most likely built at the same plant, using the same materials, by the same equipment, under the same conditions. They have all been in use in the same vehicle, and have seen the same operating conditions and usage demands for the same amount of time.

The fact that they are all starting to fail one at a time, and a consistent amount of miles apart means that their build quality was pretty good.

You really should just replace all the rest of them, and not have to keep dealing with them one at a time.

You wouldn’t just replace your spark plugs one at a time, would you?
Why are you replacing your ignition coils one at a time?


That’s the only thing I hate about coil-over-plug technology. If a coil goes bad on an old car, it won’t run. So you replace the coil, which is usually pretty cheap, and you’re on your way. On a newer vehicle, you have 4,6,8 (or 10 or 12) coils to contend with, increasing complexity. I suppose it allows the computer better control, and more energy makes it to the plug. And no plug wires to go bad.

I suppose it just isn’t cheap owning a car no matter what you have :slight_smile:

No, it’s not cheap. Each coil pack costs over $100 for the part, not including labor.

I agree with BC. The fact that all the oils are failing within a short timeframe of one another and at 250,000 miles is in my mind a testament to the quality and consistancy of the coil manufacturer.

Change the rest of them. They’ve lived their lives.

Not sure of your exact engine but it looks like each coil is about $25 at RockAuto.,carcode,1354621,parttype,7060

You can probably replace each of the remaining ones pretty easily.

I just checked your link, that is a wire. I need the whole coil pack.

What engine do you have? It’s a coil-on-plug, correct? The coil is connected to the wire.

Of course it is, but the price of $25 is only for the wire, I checked, the coil is $80.

I’d run a compression test on the engine. If the compression is dropping (and quite possible at a quarter million miles) then this can lead to improper combustion in the cylinders. In turn this causes misfires that can kill coils.

If the compression is good then one has to wonder if the gap on the plugs is too wide or if the plugs are simply being left in place for too long. Either can weaken or knock out coils over time.
It’s widely accepted that new plugs do not have to be gapped and cannot be gapped. That is an incorrect assumption.

It may be a good idea also to check the alternator DC and AC output voltages to make sure they are within spec. Perhaps excessive AC ripple may be causing the trouble.

It would help if you told us which engine you have. Try this page,carcode,1380563,parttype,7060

Coil over plug has no separate wire.

Those are $25 coils.
Will they fit the OPs engine? I don’t know.

Ultimately, its a trade off.

You want good fuel economy, good power, good emissions, and long life, you have to take a complex system of parts.

Back in the days of points and carbs, you had bad economy, short life, and constant repairs to keep the timing and dwell in spec, and the cars polluted, and gave bad gas mileage.

Switch the points for HEI, and you have slightly less unreliability, slightly less maintenance, and slightly less pollution.

Switch the carbs for throttle body fuel injection, and you have slightly better power, slightly better reliability, and slightly better emissions.

Switch the throttle body fuel injection for multi-port fuel injection, and you have better power, better reliability, more complexity, better emissions, and better gas mileage.

Switch out the distributor, cap and rotor for DIS technology with wasted spark technology, and you suddenly have even higher levels of reliability (the whole car no longer fails to start if 1 coil goes bad), and the emissions gets much better. If one coil goes bad, two cylinders are affected, so that’s an increase in complexity. Cost increases when you have to replace the coils.

Replace the DIS with coil sticks, and you increase reliability even more, increase the complexity (more coils and wiring), but now if a coil goes bad, you know exactly which cylinder it is, and doesn’t affect the rest of the engine. A smart enough engine will even shut off the fuel injector for that engine to save damage in the cylinder, and catalytic converter, plus save fuel economy.

What I’m waiting for is the day when each cylinder has its own Oxygen sensor.
I’m amazed it hasn’t happened yet in autos, but it is happening in the motorcycle world for manufacturers like Ducati. Makes for better fuel economy, better power, and better emissions, but its very easy on a 2 cylinder engine to do this.

You want good power, good reliability, and long life from your parts, when you have to replace them all as a set. No one mentions this at the time of purchase, because everyone would complain. But, when you get 250k miles from a set of coils, can you truly complain? At $100 a piece, that’s $0.0032 per mile for the full set that you got all the way to 250k miles.


You need a new mechanic, friend

Yes, I have a '04 T’bird and had the same issue with bad coils. They fail one at a time and eventually I replaced all eight and have been fine since. But, in about 50K more miles it will be the same thing. So, when one goes I’ll replace it. But when the second one goes then I’ll do the remaining 7.

Go for now, but if another fails then replace all that have not been replaced as yet.

“You want good fuel economy, good power, good emissions, and long life, you have to take a complex system of parts.”

Probably true, all except for the “long life” part. Intuitively, the more complex the system, the more trouble you’re going to have with it, and the harder it will be to repair. There were plenty of 60s and 70s vehicles that were carbureted that had decent engine life (200K miles and more), and would start and run fine in cold temps. It all depends on how much effort (and expense) the manufacturer was willing to put in to the development and debugging. The rest of the car may have rusted out to the consistency of swiss cheese, and be falling apart, but the motors would usually still be good. Oils have come a long way too since then.

I’ve also had FI cars that ran like crap when cold. It’s usually not the engineers that are at fault, but the bigwigs rushing things to market when they aren’t truly ready. Let the customer be the tester. Kind of like Microsoft.

I would agree that fuel injection and computer controls are overall a great thing for performance, drivability, economy, emissions and I have no desire to go back to a carburetor any time soon.

I have the same coil pack going bad over and over. What could it be