Engine knocking, jerky running and loss of power in 1.6 petrol engines regularly occur due to defective spark plugs and failing ignition coils. In particular, poor fuel quality and worn spark plugs make the engine sensitive to ignition problems, while individual ignition coils often fail due to heat and high load. Want to know how to recognise and prevent these problems?
Ignition problems are among the most common faults in petrol engines. The spark plug and ignition coil work together to ignite the air-fuel mixture. Both components can fail over time. In models such as the Seat Altea with a petrol engine, these complaints are often recognised as irregular idling, increased fuel consumption and an illuminated engine warning light.
The causes usually lie in the components themselves. Worn spark plugs lose their ability to produce a strong spark, while ignition coils that sit directly on or near the spark plug are extra sensitive to heat stress. Fuel quality also plays a major role: poor petrol can cause contamination and worsen engine knocking.
What exactly do a spark plug and ignition coil do
The spark plug provides the spark. This ignites the compressed air-fuel mixture at the end of the compression stroke. Without that spark, the engine cannot run. The ignition coil supplies the energy needed for that spark. It converts the on-board voltage of around 12 to 14.8 volts into tens of thousands of volts.
This high voltage is needed because the spark has to jump across in the combustion chamber under high pressure. As the spark plug wears, the spark becomes weaker. If the ignition coil weakens, the spark fails completely. The result is a misfire: the engine skips a stroke.
Why is my petrol engine knocking
Engine knocking in petrol engines often arises from premature ignition of the fuel mixture. This can be caused by:
- Poor fuel quality with a too low octane rating
- Contaminated or incorrectly adjusted spark plugs
- Carbon deposits in the combustion chamber
- Excessive heat in the engine
Poor petrol is a well-known culprit. Fuel with too low an octane rating can ignite before the correct moment. This causes a knocking sound. This knocking noise is not only annoying, but can in the long term cause damage to pistons and cylinders.
Can poor fuel cause damage
Yes, low-quality fuel can cause several problems. In addition to engine knocking, contamination in the fuel leads to soot deposits on the spark plugs. This prevents proper spark formation. It disrupts combustion. Additives in cheap fuel can also interfere with ignition.
Do you repeatedly fill up with poor-quality petrol? You will often see a combination of symptoms: jerky running, difficult starting and loss of power. The engine has to work harder. This increases the load on spark plugs and ignition coils, shortening their service life.
What are the symptoms of a defective ignition coil
A defective ignition coil causes recognisable complaints that often get worse under load or when the engine is warm:
- Irregular idle speed or jerky driving behaviour
- Loss of power during acceleration or overtaking
- Higher fuel consumption
- Illuminated engine warning light on the dashboard
- Misfires, especially when pulling away or on inclines
Ignition coils are often located directly on the spark plug. These are extra sensitive to failure. The heat of the engine can damage the secondary coil. As a result, the high voltage is no longer supplied properly. This problem often only occurs once the engine is warm, which explains why some owners experience complaints only after longer journeys.
How do you recognise a defective ignition coil in practice
In practice it is often the case that an engine can still start and run well when cold. After a few kilometres it suddenly becomes jerky. This points to a heat-sensitive ignition coil. It also occurs that the complaint only appears when accelerating or under heavier load. The engine then demands more voltage from the coil.
Fault codes in the engine management system often point to specific cylinders. Does the fault keep recurring on the same cylinder? The chances are high that the ignition coil or spark plug of that cylinder is defective.
How often should spark plugs be replaced
The replacement interval of spark plugs depends on the type of plug and the driving conditions. Standard spark plugs generally last between 30,000 and 50,000 kilometres. Platinum or iridium plugs can last up to 80,000 or even 100,000 kilometres.
Do you drive intensively, make many short trips or use poor-quality fuel? Wear will increase more quickly. The electrode of the spark plug gradually wears due to spark formation. The gap becomes larger. The spark becomes weaker. Contamination by soot or oil accelerates electrode wear.
When is it time to replace spark plugs
Replace spark plugs when you notice one or more of the following signs:
- Hard starting, especially with a cold engine
- Irregular idle speed when idling
- Reduced performance or poor acceleration
- Increased fuel consumption
- Engine warning light that stays on
A visual inspection can also tell you a lot. Spark plugs with black soot deposits must be replaced. Spark plugs with whitish-grey discolouration or damaged electrodes must also be removed. Check all spark plugs during servicing. Do not just look at the defective plug. Often, several spark plugs show similar wear. Replace them all at the same time to prevent future problems.
Practical tips for diagnosis and maintenance
With ignition problems, fast and targeted diagnosis is important. This prevents further damage and saves unnecessary costs:
- Read the fault codes with a diagnostic device. This will show you which cylinder is causing problems.
- Visually inspect the spark plugs for wear, soot, oil or damage
- Test the engine immediately after starting or while driving. Some problems only become visible then.
- Check whether the complaint occurs under load or when hot. This points to an ignition coil problem.
- In doubt? Replace both the spark plug and the ignition coil of the affected cylinder.
For persistent complaints, an oscilloscope measurement can help. This allows you to detect defects in the secondary winding of the ignition coil. This measurement shows whether the high voltage is being built up correctly. It also shows whether the high voltage is being delivered correctly.
Prevent problems with preventive maintenance
Regular maintenance extends the service life of spark plugs and ignition coils. Wherever possible, refuel at reliable filling stations. This ensures fuel quality. Replace spark plugs according to the manufacturer’s maintenance schedule. If you notice complaints, have a check carried out immediately.
Also check the other components in the ignition system, such as coils and spark plug leads. This check applies when your car is equipped with these components. A weak link in the system can impair the performance of the entire engine. Check multiple components at the same time. You will then get a more complete picture of the condition of the ignition system.
What you need to remember
Spark plug and ignition coil faults are common causes of poorly running petrol engines. Recognise the symptoms early. Take action. Otherwise, small complaints will lead to costly repairs. Poor fuel quality makes the problems worse, so pay attention to where you fill up. Replace spark plugs in good time. Check the ignition coils if you suspect defects.
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Frequently asked questions
You will usually recognise defective spark plugs or coils by an irregular or jerky running engine, especially at idle, and clearly noticeable loss of power when pulling away or under load. Fuel consumption often increases and the engine warning light may come on, while the engine sometimes “hesitates” or skips a stroke (misfire). With coil problems, the complaints often get worse as the engine becomes warmer or is more heavily loaded. If in doubt, it is wise to have the fault codes read and the spark plugs visually checked for wear or contamination.
Major causes of problems with spark plugs are wear and contamination (soot or oil), which makes the spark weaker and leads to misfires. For coils, heat and ageing are the main causes: the winding can become internally damaged and can then no longer supply sufficient high voltage under load. You can prevent this by replacing spark plugs on time according to the maintenance schedule, keeping the engine in good condition (no excessive oil or soot formation) and having fault codes and ignition components checked immediately in case of complaints. When replacing a defective coil or spark plug, immediately have the other ones checked as well to reduce the chance of recurrence.
Defective spark plugs or coils cause misfires, which make the engine run irregularly, deliver less power and respond more slowly. Because not every combustion takes place properly, fuel consumption rises noticeably. Incomplete or failing combustion can also cause extra soot and heat, which in the long term accelerates wear and potential damage to the engine and catalytic converter. Driving for a long time with these defects therefore shortens the service life of the engine and exhaust aftertreatment.
Yes, it is possible for an enthusiast to replace spark plugs and, in many modern engines, also coils, provided you have basic tools and technical knowledge. It is important that you use the correct spark plugs and coils specified for your engine, and respect the tightening torque of the spark plugs to prevent damage to the cylinder head. Always work on a cold engine, keep the spark plug wells clean (do not let dirt fall into the cylinder) and check connectors and cables for damage. If you are unsure about fault codes, misfires or irregular running, diagnosis (for example reading out the system) beforehand is essential to avoid replacing parts unnecessarily.