Young mechanic wiping his hands while repairing car engine in auto repair shop.

Explained: Coil Packs in You Car

Have you ever felt that your car is suddenly feeling a little sluggish, or sounding slightly off? Perhaps you’ve been down to your local garage and they’ve told you you’ve got a dodgy coil pack that needs replacing. But what are they actually talking about when they say that? Scrap Car Comparison’s Car Care guide turns its attention to helping you out and busting some of the jargon that may be going over your head.

But first, if your problems stretch further than just a faulty coil, then you may find that repair works are just too costly for you to realistically consider having them carried out, and as a result you’re now watching all of your options disappear around you. Luckily, that’s where Scrap Car Comparison comes in. No matter how badly damaged your car or van is, we’ll be able to find you the very best price in less than a minute and, no matter where you call home, we’ll even come and collect it from you absolutely free of charge.

A mechanic holds a replacement set of ignition coils

What is a coil pack on a car? 

A coil pack is a collection of ignition coils which act as a transformer, taking low voltage from the battery and giving it a boost so it can bridge the gap in a spark plug. This then causes the fuel and air to ignite, creating the spark needed to get your car moving along.

Where is the coil pack located? 

The location of your coil is likely to change depending on the age of your car. Older vehicles will likely see the coil pack mounted on the engine closer to the distributor, which would then distribute (hence the name) the electricity to the spark plugs through electric wires.

More modern cars are much more likely to feature multiple coils due to the fact they use a computer to fire the spark plugs rather than a distributor, meaning the coils can be placed directly in the spark plugs themselves, rather than run through high voltage spark plug wires. 

How to test the coil pack

You’ll likely be able to identify a faulty coil pack when your car fires up, as they can be the reason for a multitude of concerns, including misfires, backfires, the inability to start, low power, poor fuel consumption or the smell of unburnt fuel. Of course these could be as a result of other issues as well, but faulty coils have been known to cause all of the problems above.

The easiest way to check for a faulty coil on a car built after 1996 is to get a diagnostics computer and plug it into the OBD II (on-board diagnostic) port with misfire detection, which will cause the check engine light to come on if there is a regular misfire. By using the diagnostic computer, if you see error code P030X – then whatever number ‘X’ is will denote the cylinder that has failed.

This still doesn’t necessarily mean it’s the coil that is faulty, but one quick check can confirm that diagnosis for you. Simply swap the coil from the cylinder denoted on the error code with one of the ‘good’ cylinders, and if the code has moved to the other cylinder, then you know that the coil is the reason for the failure.

How do coil packs go bad? 

One of the most common reasons for coil packs going bad is just plain and simple wear and tear. The insulation between the windings and the coil itself gradually wears away over time, which can cause the oil to overheat. Overheating isn’t good when it comes to coil packs, and it can have a negative effect on their ability to conduct electricity. Vibrations can often cause shorts or breaks in the secondary windings, which are less than ideal situations for your coil packs to find themselves in.

How long do coil packs last? 

As with any component in a car, there is no hard and fast rule as to how long something will last, or a ‘use-by’ date, but as a general rule of thumb you’ll want to replace your coil packs every five years, or 120,000 miles. Extended exposure to both heat and vibrations will cause them to wear out much faster.

Are coil packs universal? 

In a word: no. While on the face of it, they may look identical, you’ll need to make sure that the coil you’re buying has the correct ohm (the unit of electrical resistance) rating, or it’s not going to work.

Can a bad coil pack cause a misfire? 

Quite often a bad coil pack can cause a cylinder to lose its spark – as we’ve discussed above – so it’s entirely plausible that a misfire is being caused by a faulty coil. If your engine sounds off, or feels like you’re not getting the level of grunt you’re used to, then either check it yourself or take it to the local garage just to be sure.

Do new coil packs make a difference? 

When looking to upgrade your old car, one of the most common areas people look at is boosting their horsepower. Over time, several of those horses will have bolted out of the stable, so modifications or improvements to get you back to that original figure (or above it) are absolutely an option. Swapping out your old, defective coil packs for newer ones do offer this benefit, and you’ll likely find a boost to your horsepower reading on the dyno once they’ve been replaced.

Are coil packs covered under warranty

Due to the nature of a coil pack being what is known as a ‘wear-and-tear’ product, you’re unlikely to find them covered in extended warranty packages, much in the same way your oil filter, fuel filter, clutch or brake pads won’t be covered. You’ll just need to keep them in mind when you take your car for its regular services.

Do diesel engines have coil packs?

Diesel engines work on compression ignition, rather than spark ignition, so you won’t find any coil packs under the bonnet of your diesel-powered car. As a result you won’t find any spark plugs either; in their place you’ll find glow plugs, which act like small electric heaters, using heating due to resistance during electrification.

If you think your car could be fixed with just a simple switch out to a new coil, then you could be happily motoring away in next to no time at all, however, if you’ve looked and found the problems run deeper, then maybe it’s time to consider sending the car on one final journey. Scrap Car Comparison is here for when it looks like there’s no possible solution for your car. All it takes to find the best price is to either call our office on 03333 44 99 50 or use our instant quote generator and within a minute you’ll find out just how much your tired old vehicle could be worth.

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