How Long Can You Drive With a Faulty Coil Pack? Expert Advice!

You’re mid-journey on a long drive, and the engines are hesitating, misfiring, or stalling. The culprit could be, or you may know, its a faulty coil pack. You’re probably miles from home, so you’re now faced with whether you can continue despite the issue, and if so, for how long?

How long you can drive depends on the condition of the coil pack and how the engine responds to the bad ignition coil. A defective coil pack may begin to cause damage to other parts of the engine, which could lead the car shutting off.

It would help if you first understood the function of an ignition coil pack. Then, you can understand how to spot problems early and judge how long you drive with a bad ignition coil. All of which is covered in this article. 

What is an Ignition Coil Pack? 

There is generally some confusion over a coil pack and the ignition coils; however, coil packs are a distributor-less ignition system(DIS) replacing the old mechanical distributor ignition system.

To summarise the coil pack’s job without boring you with the finer details, the coil pack produces the high voltage needed to ignite the air-fuel mixture within each engine cylinder and keep the engine running.

The process begins when the car’s battery sends low-voltage (12 volts) electricity to the ignition coil. Inside the coil, this electricity is stepped up to a higher voltage, as high as 100,000 volts or as low as 20,000. Depending on the type of ignition coil, this high-voltage current travels to the spark plug. Here, the voltage causes a spark to jump across the plug’s gap, igniting the air-fuel mixture in the cylinder.

This ignition creates a mini explosion, pushing the piston down, which drives the crankshaft. This is basically the combustion process of a car’s gasoline engine. 

As I mentioned, there are a few different types of ignition coils:

You’ll only find conventional-type ignition coils on older cars; however, you will find one of the other three types on all-new petrol-engined vehicles. Then to confuse things even more, there are several different types of each; however, the design is irrelevant because they all do the same job. 

How Long Should a Coil Pack Last?

A coil pack should last the life of a vehicle, but realistically that’s not the case, and most tend to last around 100,000 miles or ten years. Types of driving and climate also contribute to its life expectancy. 

There are certain vehicles I won’t name, but they are extremely common for coil packs to fail every couple of years, so please bear in mind that vehicle-specific designs also are a factor. 

How long can you drive with a bad coil pack? 

There is a scenario or two where driving with a bad coil pack for a reasonable length of time is possible. If the check engine light is on, you are experiencing no other symptoms, and you have confirmed it’s a faulty coil pack, you could continue driving.

However, to be clear, as soon as the engine begins to misfire or you experience other issues, you should refrain from driving. This could be 5 minutes, 50 miles, or five months; there is no set time frame for the speed of a coil pack breaking down. Unfortunately, it’s a catch-22 scenario; the more you use the vehicle, the quicker it will fail. 

faulty coil

Signs you should stop driving with a faulty coil pack 

If you notice a faulty coil pack can cause any of the signs below that you should stop driving. 

Illuminated check engine light

This is often the first sign of a problem. Your car’s onboard computer system can detect issues with the coil pack, triggering the check engine light to come on. The only way to confirm this is by using an OBDII scanner and confirming the fault code. There are 1000s of different reasons for the check engine light to come on, so you wouldn’t ever assume, especially if the only symptom is an illuminated check engine light. 

Loss of Power 

Another early sign of a faulty ignition coil is a noticeable reduction in power. The engine’s power will be reduced without a strong spark delivered on time. This makes the car feel less responsive and may hesitate or jerk when you press the throttle.

Engine misfiring

A failed coil pack is one of the most common misfire causes. The engine will misfire without a consistent high voltage supplied to each spark plug. At this point, you should avoid driving the vehicle as you are causing more damage to the engine by continuing. 

Engine backfires

Another sign attributed to a faulty coil pack is the engine backfiring, especially after heavy acceleration and then letting off the gas pedal. Unburnt fuel exits the combustion chamber through the exhaust, where it ignites due to the exhaust’s high heat and pressure.

A loud bang, black smoke from the exhaust pipe, and a strong gas smell are typical indicators of an engine backfire.

Difficulty starting and engine stalling

A defective coil pack makes it harder for your engine to start. This is because the spark plug doesn’t get the voltage needed to generate a spark, resulting in a hard start.

A bad coil pack might also make your car stall when you come to a stop, and it will then be hard to restart it again.

What Happens if You Drive With a Bad Coil Pack?

When the ignition coil doesn’t work, the spark plug fails to generate the spark needed to ignite the fuel in the engine. The fuel pumped into the engine won’t burn without a spark. Essentially the engine won’t run correctly and will misfire; continued driving will cause damage to other components, such as: 

  • Catalytic converter – Unburnt fuel is then forced into the exhaust system. If the catalytic converter is hot enough, the unburnt fuel can ignite in the exhaust system, which is usually the reason for a blocked catalytic converter
  • Engine oil – Some unburned fuel might also mix with the engine’s oil, which is not so much of a problem but can lower the oil’s quality and ability to lubricate the engine.
  • Damaged wiring –  The faulty coil pack can cause problems with the wiring. Even though the coil may be faulty, it can still produce high voltages but won’t send it to the spark plug; this can cause the coil to overheat, damaging the wiring. 
  • Engine damage – Driving with a misfire or backfiring engine puts extra pressure on its internals. The cylinder block, pistons, rings, and rods are all components that will quickly fail with prolonged driving. 

Final Thoughts

Saying how far you can drive with a malfunctioning coil pack isn’t straightforward. Sometimes, immediate repair isn’t feasible. But providing you can be sure no other damage is being done, which depends on the symptoms, it may be possible to carry out a few short journeys. 

But caution is necessary. A faulty coil pack could cause damage to other engine parts, potentially leading to a breakdown. Therefore, upon spotting any signs of a defective coil pack, the smartest approach is to fix it immediately.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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