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Things not running quite right with your vehicle? If your Check Engine light is on and your vehicle’s engine is stumbling, missing, and lacking power, you might have an ignition problem.

Usually you can identify one of several issues causing most ignition problems. If your check engine light is on or flashing, finding the problem is easier. AutoZone’s free FIX FINDER service can help you identify the most likely part causing the issue and make a recommendation for repair – or finding one of our Preferred Shops in your area can help you track down the problem.

Common Ignition Problems

1

Faulty Ignition Coil, Spark Plug, or Spark Plug Wires

An ignition issue can be caused by a faulty or failing ignition coil, spark plug, or spark plug wire set. These critical components of your ignition system keep your engine running smoothly. If they have a problem, you’ll notice a rough ride, engine misfires, and possibly decreased gas mileage, along with in most cars, a Check Engine Light (CEL) for a misfire.

Often times, replacing the failed or failing part will correct this issue.

Ignition coils and wire sets are fairly straightforward to replace. However, some applications will require removal of major components such as the upper intake plenum manifold. Reference a repair guide for more specific information for your vehicle. We highlight how to properly test your ignition coils, or troubleshoot problems here.

Spark plugs may require a bit more attention on some vehicles. Some can be very easy to get to and replace, where other ones are a long, complex job depending on their location. We have a guide on replacing spark plugs. Some spark plugs need to be gapped and have anti-seize applied before installing and some do not. Check the spark plug manufacturer’s requirements.

Spark plugs should always be installed with a spark plug socket and tightened to the proper torque. If you need a torque wrench, borrow it from AutoZone through the Loan-A-Tool program.

2

Crank Position Sensor Failure

Any modern ignition system that doesn’t use a distributor has to have a method at which to determine the precise moment to fire the ignition coils. To do this, a crank position sensor is used, which is essentially a magnetic trigger. At the precise moment in revolution, the sensor picks up a trigger point in the rotating crank, and sends signal. When this sensor fails, this signal is lost. Sometimes, it the part fails completely and you have either a dead vehicle on the road, or a no-start situation. Other times, the problem can be intermittent, leading to misfires, or stalling issues. In most cases, when this occurs, the vehicles engine computer will pick up a code for crank position sensors.

3

Cam Position Sensor

Like it’s cousin, the crank position sensor, a cam position sensor does the same thing on the engine’s camshafts, or multiple camshafts. These devices read the position of the cam in respect to ignition timing, to either advance (make the spark come earlier) or retard (make the spark come later) in the stroke.

When a cam position sensor goes awry, you can experience much of the same issues – misfires, lack of power, poor gas mileage, or a no-run / no-start situation. Like most sensors, it’s also picked up by the vehicles engine computer, so if there’s a fault, an engine code will pick it up.

4

Distributor Pick-Up Coil / Hall Effect Sensor

Very similar to a crank position sensor, in distributor-style ignition systems that do not use breaker points, each distributor has a pick-up coil, or hall effect sensor (same thing) that reads a cog wheel inside the distributor to accurately pick up and tell the precise moment when to send a signal to the coil to fire.

When a pick up coil goes out, you generally have a no-start situation. Many people often think this is the ignition coil, but often times, the pick-up coil is the culprit. Changing these coils can be difficult, because often, the distributor must be completely removed to gain access to it.

5

Ignition Module

Many vehicles made in the last 10 years no longer use a proper Ignition Module, and instead house its function either in each individual coil, or in the vehicles onboard computer. Ignition Modules were the standard for many electronic ignition systems from the late 70’s all the way through the early 2000’s. Many foreign vehicles refer to the unit as a power output stage control, or ignition control unit, but they are all the same thing.

These devices help process the signal from a crank position sensor or pick-up coil in a distributor system and distribute the signal of when the coil should fire. When they go out, you can have a misfire, coil packs not functioning properly, or a no-run / no-start situation.

Pinpointing an issue

It’s important to remember, that there are a multitude of other sensors and situations on a vehicle not related to the above scenarios that can cause a misfire. Fueling, vacuum, engine timing – to name a few – can also cause issues that will need to be investigated. Remember on any of these components to always carefully inspect the electrical connectors and related wiring for shorts or potential problems before changing parts. To help pinpoint an ignition issue or decode a check engine light, stop by your local AutoZone to use our free Fix Finder service to help identify the most likely problem and make recommendations for a repair – or – if the diagnosing the problem proves to be difficult, one of our Preferred Shops can lend a hand!

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Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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