Ignition system: spark plugs, coils, leads — how to buy well
What the ignition system includes
In a petrol engine it is the spark plugs, the coils (one per cylinder or one for two), high-tension leads on older cars, and sometimes an ignition module or distributor. In a diesel, a similar job is done by glow plugs, which help it start in the cold. So a diesel car does not need spark plugs but glow plugs, and this is a common mix-up in requests.
As a set or one by one
Spark plugs are changed as a full set, by the number of cylinders: four, six, eight. Coils usually last longer, but if one fails, think about the condition of the rest, especially at the same mileage. Does the engine “misfire”, idle unevenly, burn more fuel? First check the spark plugs and coils: it is the cheapest way to diagnose.
What to put in your request
- Which part — spark plugs, glow plugs, coil, leads, module, distributor.
- Model and year — for example, Suzuki Swift, 2012.
- Engine — capacity and code: 1.2 petrol; the plug type depends on it.
- Quantity — a set of 4 or single pieces.
- Original or aftermarket — NGK, Bosch, Denso, Champion or the car maker’s original.
- Part number — from the box of the old plug or the catalogue.
- Condition — for plugs and coils almost always new.
- City, delivery and budget.
Example: “I need a set of spark plugs for a Suzuki Swift, 2012, 1.2 petrol engine, 4 pieces. NGK or Bosch, as per the maker’s catalogue. Courier delivery to Brisbane. Budget up to $43.”
How to compare offers
Write a request, and auto parts sellers will reply in the chat: brand, set, price, delivery. The platform shows first the offer that is best on content, with reviews of the seller beside each. Sellers see their place among competitors, so they often cut the price or offer free delivery. Your number stays hidden. More about the process is on the “How it works” page.
Compare offers by what is actually in the box: a plug with an iridium or platinum electrode lasts longer but costs more than an ordinary nickel one; and on turbo engines and cars with CNG kits the maker often requires a special type of plug. Ask about the gap too: many plugs are sold pre-set, but it is worth checking. Beware of fakes: the quality of the packaging, a hologram, clear printing and weight help tell the original, and a reliable seller will gladly send a photo of the box.
Common mistakes
Buying plugs “by engine size” without checking the code. Fitting a “cold” plug on a motor that needs a “hot” one. Changing one coil and leaving the old ones. Tightening a plug without a torque wrench and stripping the thread in the head. For related parts see engine and fuel system, and for a general overview see car parts.
