HOW TO RENEW SPARK PLUGS
1 In most cases, the spark plugs are
not visible, so several components will need to be removed to access them. Take this MINI Cooper S (R53), which has a supercharger intercooler fitted over the top of the engine that requires removal first.
2 An upper engine cover is usually fitted 2
across the top of the engine, so it will need to be removed to access the spark plugs. This is either clipped into position or located with screws. In some vehicles, the oil filler cap and dipstick will need to be extracted before lifting the cover.
3 Engines with a rear-wheel-drive layout, 3
or a vee formation engine, may require component removal. Take this Jaguar S-TYPE – the windscreen wipers, scuttle trim panel and strut brace have to come off to remove the inlet manifold and access the offside spark plugs (three of the six plugs fitted).
4 It’s not just V6/V8 engines 4
that may need their inlet manifold removing to access the spark plugs. When we replaced the spark plugs on a 2003 2.0-litre Kia Sportage, the alloy induction pipe and resonator box had to be taken off to access them.
5 Breather pipes and electrical 5 plugs may need to be detached to allow parts to be removed, or to make space for accessing the spark plugs. Make a note of what you disconnect and make sure they are all refitted afterwards.
6 In some cases, the throttle body and inlet manifold have to be taken off, which may mean a fuel hose or pipe has to be disconnected. This may result in a fuel spillage, so clamp any fuel hoses and have paper towels at the ready to mop it up.
7 Induction components, such as pipework and the air filter housing, may need to be removed to make space to access the spark plugs. This is often applicable on V6 and V8 engines, but can also be the case with in-line engines too.
8 If the inlet manifold needs to be disconnected to access the spark plugs, you may need to replace its gasket. Lift it away carefully, looking for additional parts to detach, such as the brake servo pipe.
9 A spark plug cover is often secured across the top of the spark plugs and needs to be removed. It’s usually secured with several small bolts or screws. The HT leads are usually routed underneath it.
10 If a coil pack is fitted over the top of each spark plug, then its electrical plug will need to be disconnected and the coil removed. The coil pack will probably be secured using one or two bolts, so undo them next before carefully lifting the coil packs off each spark plug.
11 Where an HT lead is fitted directly onto the top of the spark plug, avoid pulling on the HT lead when attempting to remove it. This can damage the lead, resulting in a broken connection and a greater risk of arcing and misfires.
12 Use a suitably sized spark plug socket and 3/8in ratchet with extension bars (if required) to undo the spark plug. Make sure the socket is fully seated before undoing the spark plug. It may be tight – see our Typical Trouble steps for more information.
13 Lift out the spark plug and, if you are fitting a new one, make sure they are both the same thread size and length of thread. The old spark plug may tell you whether the engine is running too lean or too rich, or just right.
14 For spark plugs with a single electrode, check the gap with feeler gauges and adjust with a gapping tool (if required). On multi-electrode plugs, no gap adjustment is required. Some mechanics choose to apply a fine smear of copper grease around the threads of the spark plug to reduce the risk of it seizing, whereas others dry-fit them afterwards.
15 Lower the spark plug into position and carefully wind it into the cylinderhead, being very careful that it doesn’t cross-thread itself. Then fully tighten it to the recommended torque setting using a torque wrench.
16 Refit all remaining parts. We recommend adding a tiny drop of dielectric grease onto the top of the spark plug or inside the coil pack or HT lead connection, to achieve a good electrical contact and reduce the risk of corrosion.