Citroen Grand C4 Picasso Spark Plugs

Standard copper plugs want changing around every 30,000 km. The iridium and platinum plugs fitted to the newer C3, Xsara and C3 Aircross models last 60,000 to 90,000 km because their fine centre electrodes erode far more slowly. Your handbook gives the figure for your engine. Whatever the interval, inspect at every major service — plugs tell you more about engine health than almost any other part you can remove in five minutes.

NGK plugs run roughly R19 to R399 each depending on grade, and a four-cylinder set is the normal job. Ask through our form with your engine code and we will include the fitting. One thing worth flagging: on coil-on-plug engines each coil has to come off to reach its plug, which adds labour compared with the older lead-and-distributor arrangement.

Rough idle, hesitation on acceleration, consumption up and a misfire code against a specific cylinder. The confirmation is in your hand once one is out — a worn plug has visibly rounded electrodes and a wide gap. What it looks like beyond that is diagnostic: black dry soot means a rich mixture, oily wetness means oil is getting past something, and pale white deposits mean it has been running hot.

Most C3 petrol engines run NGK iridium plugs, but the exact part number depends on which engine you have — the 1.2 PureTech and the older 1.4 TU take different plugs. Check your handbook or a parts catalogue against the engine code rather than the model, because the wrong heat range causes exactly the misfiring and fouling you were trying to cure.

Yes — worn, fouled or cracked plugs are the leading cause of misfires and the cheapest thing to rule out. Before anyone starts replacing coils or injectors, pull the plugs and look at them. They also point at the underlying problem: oil fouling suggests valve stem seals or piston rings, dry black soot suggests a rich mixture from a lazy sensor. The plugs are evidence as much as they are parts.