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How to Detect Faulty Coil Pack Symptoms

The coil pack has a major role in starting the car and keep the engine running without any trouble. The spark plug in the engine requires a high voltage for creating a spark and starting the combustion process. The coil pack does the job of producing that required high voltage. The engine won’t start, and your car won’t function smoothly if there’s any problem with this component. So, you need to be aware of bad coil pack symptoms because any problem with it will lead to engine performance issues.

bad coil pack symptoms
To bee aware of bad coil pack symptoms because any problem with it will lead to engine performance issues.

What Is Coil Pack?

A coil pack is an electronic piece of equipment within the ignition system. This electronically-controlled pack consists of ignition coils that are controlled by the car’s main computer. The main function of the coil pack is increasing and building the energy needed, then releasing the voltage through the spark plug cables. When the energy reaches the spark plugs, it starts the combustion process. 

how to tell if coil pack is bad
A coil pack is an electronic piece of equipment within the ignition system

In the new car model. The coil pack is replaced by the distributor. This is typically because the coil pack is more reliable and consistent than the distributor. Moreover, the coil pack provides a better spark, which causes more efficient and quicker combustion, along with higher horsepower. 

Faulty Coil Pack Symptoms

Your car won’t perform properly if there’s any problem with the coil pack. The usual signs of a bad coil pack is the answer for the question of how to tell if coil pack is bad.

  • The engine is misfiring
  • The car engine making louder sounds than usual
  • Engine is idling roughly
  • Flames coming out of the carburetor
  • Backfiring
  • Blinking engine lights
  • A drop in RPMs during acceleration
  • Exhaust puffing smell of gasoline
  • Engine light coming on
  • The car won’t start

1. The engine is misfiring

Engine misfiring is one of the bad coil pack symptoms. Trying to start the engine of such a vehicle will result in engine misfiring that sounds like a coughing, sputtering noise. When driving at high speeds, jerking and spitting will be seen in the behavior of the vehicle. A vehicle with a failed ignition coil will also result in vibration when it is idling at a stop sign or light.

signs of a bad coil pack
Trying to start the engine of such a vehicle will result in engine misfiring that sounds like a coughing, sputtering noise.

2. Engine is idling roughly

Another symptom of  weak coil pack symptoms is rough idling of the engine. It feels like your vehicle is missing some power when driving. Rough idling is what happens when coil pack goes bad so you need to fix it right after you find this symptom.

3. Backfiring

Backfiring caused by your vehicle can indicate the symptoms of the ignition coil failure in its early stages. Car backfiring occurs when the unused fuel in the combustion cylinders of the engine leaves through the exhaust pipe. If this problem is not checked and fixed, it can result in costly repair. If your car has backfiring, you will see the emission of the black smoke through the exhaust pipe.

signs of a bad coil pack
If your car has backfiring, you will see the emission of the black smoke through the exhaust pipe.

4. Exhaust smoke comes out

The bad coil pack symptoms can also be determined by the exhaust smoke coming out when the vehicle is running. The smoke comes out intermittently instead of in a normal steady stream

5. A drop in RPMs during acceleration

If you have a faulty coil pack, the drop in RPMs during acceleration can happen. It can be determined by watching the RPM gauge while driving. During acceleration the check engine light either comes in intermittently or blinks.

what happens when coil pack goes bad
If the drop in RPMs during acceleration can happen, you may face a faulty coil pack

6. Lower fuel economy

If your ignition coil does not transmit enough energy to the spark plugs in your car, your vehicle will have to burn and use extra fuel. It is the only way that the vehicle can keep running – by burning the extra and residual fuel. If your car is getting very poor gas mileage and a lot lower than normal, then you might have coil pack problems.

7. Engine light coming on

So, how do you check for a bad coil pack? You can check the engine light! Usually, the engine light will turn on in your dash and the engine code is P0351 when scanning using a car diagnostic tool. The easiest way to tell ignition coil pack symptoms is scanning the error code. So by seeing the error code, you can check the engine light and figure out what is the coil pack problem.

 how to test a coil pack
By seeing the error code, you can check the engine light and figure out what is the coil pack problem.

8. The car won’t start

The car does not start also is one of the bad coil pack symptoms. If you try to start your car and it seems not to start, it is possible that your car has a problem with the coil pack.

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How to Diagnose a Faulty Coil Pack

The ignition coils are reliable but they can fail for various reasons such as vibration and extreme heat. However, voltage overload caused by plug wires or bad spark plugs is the most common reason for their failure.

If you spot any of the bad coil pack symptoms, you should diagnose them to see if they have any problem. A few methods of how to test a coil pack have been discussed below:

Use an Ohmmeter

You have to measure the coil’s primary and secondary resistance to find out if it’s in a fully functioning condition, and you have to use an ohmmeter to do that.

Connect the ohmmeter to the high voltage output terminal and the positive (+) terminal to measure the secondary resistance. Reading between 6,000 and 8,000 ohms is normal if the coil is new while some coils may read more than 15,000 ohms.

how do you check for a bad coil pack
Reading between 6,000 and 8,000 ohms is normal if the coil is new while some coils may read more than 15,000 ohms.

Measure the secondary resistance by connecting the ohmmeter to the high voltage output terminal and the positive (+) terminal. A reading between 6,000 and 8,000 ohms is normal if the coil is new while some coils may read more than 15,000 ohms.

Other two ways of testing the resistance are to use either a spark tester that is inexpensive and available at most auto part stores or an ignition coil bench tester that is available in auto repair shops.

No matter which method you apply, never try to pull off the high voltage output wire or a plug wire to test for a spark. An open wire is risky as it can give a severe shock. Besides, sudden unplugging of wire can damage the coil by increasing the voltage demand. So, when you detect bad coil pack symptoms, follow a proper method to test the coil’s resistance.

Sum Up

The 8 symptoms above are the bad coil pack symptoms. You can check with your car, if your car has one or more than one symptoms, it is possible that your car has a faulty coil pack. Bringing your car to the mechanic to diagnose your car and have the repair when needed.

Check out other useful car maintenance tips provided by Car From Japan experts here!

 

10 Comments
  1. Derek says

    Rather than test primary and secondary resistances you tested secondary twice. Great otherwise

    1. Trang Tran says

      Thank u for your comment

  2. Amos nyakeya says

    Hi
    I wish to know the problem with my car. When driving at 70km/h, the wheels start vibrating, what is the cause?
    Thank you

    1. tom scally says

      Balance the tires and check for any tire blemish / damage

  3. Mathews says

    My car when I start the engine, it’s start and stop then when I start again it’s start but the engine is vibrate.And when I put first gear I must use accelerate harder to able to move. And the rev counter it’s goes up and down when I stop at the stop sign

    1. tom scally says

      Sounds like a vacuum leak

    2. tom scally says

      Possible vacuum hose needs replacement or reattached

  4. Michael Kay says

    Good tips

  5. Shawn says

    Why will it fire on 3 and not the other 3 on coil pack

  6. KEV WATSON says

    I have a problem with my car, as uim driving it suddenly shuts down and stops, then it wont even turn over for a few attaempts and then restarts again after 5 minutes, could this be coil pack?

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