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How to tell if coil pack is bad Symptoms, indications and precautions

How to tell if coil pack is bad: Symptoms, indications and precautions

Testing your ignition coils is essential to getting the most out of your vehicle. If you suspect that something is wrong with one, some basic testing can determine which coil needs repairs and prevents unnecessary problems for yourself in addition to avoiding costly engine replacements or other major maintenance costs due to an issue like this.

Newer vehicles use a coil pack instead of the distributor. They are electronically controlled packs that create sparks for each engine cylinder’s spark plug and fire much less often than distributors, which means they’re more reliable because there isn’t any moving parts involved in their operation. In addition to creating better combustion with power gains due to this improved system performance (due mainly from reduced fouling).

Today’s carmakers also say these newer designs produce cleaner emissions thanks largely to advances made by emission control experts over recent years—especially when it comes down lighting up high-mileage curves at legal speeds. New cars equipped with coils offer significantly greater torque production since you don’t need anything but electricity running through them like old school mechanical ignitions did.

In this post, we are going to answer the question that how to check if the coil pack is bad or faulty. Let’s find out the symptoms that indicate about the coil pack’s bad state.

How does the coil pack work?

First, it is significant to know that how does coil pack work actually?

There must be a fire (from a high voltage source) when a spark is produced at the spark plug, so more and more fuel is burnt in the cylinder. So, the coil pack generates energy equivalent to 50,000 to 75,000 volts at the start of the combustion process.

A signal is delivered by the car to the ignition control and a voltage is released from the coil pack through the means of spark plug cables to the spark plug. As this spark traverses through the spark plug, it travels from the spark plug to the ground and an explosion of fuel-air mixture is generated inside the cylinder chamber.

Common symptoms of the faulty coil pack

If you are wondering how to check if coil pack is bad, it is significant to have some knowledge about the common symptoms that indicate about the faulty coil pack.

Misfiring – One of the most common symptoms of a bad coil pack is misfiring. If the coil pack is faulty, there will be a loss of fire in cylinders which is termed as Misfire. It will occur in a specific or random cylinder. It causes drag on crankshaft which ultimately leads to poor performance of engine. Usually, the specific cylinder misfires are easy to be diagnosed as compared to the random one. If the car starts lacking acceleration, a coil pack may be the reason behind it.

No-Start condition – If there is a no-start situation, you must pay attention to the coil pack. Particularly, in older vehicles the ignition coil will be the culprit in this situation. Since there are many cases in which coil pack gets failed between the last-run and the next start-up phase.

Idling – Rough idling (or hesitation under load) is another condition which might be the symptom of a faulty coil pack. Usually, the coil problems which are misfires also result in rough idling. But if the vehicles are not capable of detecting misfire situation, this rough idling situation can indicate a faulty coil (or the overheated coil).

How to check if coil pack is bad Or faulty?

There are different ways to check if coil pack is bad and needs to work on. Check out the following ways:

  • Spark test

One of the most important things to remember regarding coil pack failures is that it becomes weak when it gets failed, but the vehicle may run fine. But it can generate misfires when there is a load or acceleration. So, the coil gets failed entirely other moments and finally stops functioning. In such situations, the spark test or active analysis is the only way out for checking coil pack.

The spark test (also referred to as active analysis) is performed with different tools or procedures. With any of these procedures, the coil’s output is analyzed while the vehicle is in running mode. While performing this test, you must keep it in mind that if coil wires are yanked off in the vehicle’s running mode, this may cause a serious injury. Power balance test is another method that can be applied to isolate where the cylinder issue is.

  • Normal inspection

If you want to know how to check if the coil pack is bad, another method is to perform a general inspection. Look at the coil thoroughly and carefully to determine if there are any burns, cracks or leakage, or melting issues in older coils. If there is any, that obviously points to the faulty coil pack.

  • Testing coil windings with multimeter

One of the most convenient ways to check coil pack is to test the windings with a multimeter. Ohm’s resistance is checked this way and the method works to some level. But this is not that much efficient method because you ate not capable of estimating load or measuring the coil while operating situation. So, the weak coils may still pass the test and you cannot tell that in actual coil pack has issues.

But the testing of coil’s windings can help out in determining the major issues with coil. Every ignition coil has two separate coils that are wrapped around each other. These are basically the primary and secondary windings.

  • Swapping

The easiest and straightforward method is swapping the coil with another unit on the vehicle. So, you can perform diagnosis in an easy manner to determine if the coil pack has issues. This method performs well on vehicles with single coils, coil on plug or multi-packs.


The above methods will help you determine if there is any fault with coil pack. This way you will be able to take some actionable steps to sort out the issue. Leave your comments below to share your experience with the coil pack and what method you have performed in order to know if coil pack is faulty.

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