Mazda Misfire Diagnosed and Repaired at Our Walsall Garage

A Mazda came into us recently with a misfire that the owner had been noticing for a little while. The engine was running roughly, particularly at lower revs, and the car felt hesitant when pulling away. These are the kinds of symptoms that can have several causes, so the first job was to pull the spark plugs and have a proper look at what was going on.

Oil Had Got Into the Spark Plug Wells and Soaked the Plugs Through

When our mechanic removed the spark plugs, it was immediately obvious what the problem was. Oil had been leaking down into the spark plug wells, which are the tubes that the plugs sit inside in the engine head. The plugs themselves were wet with oil. A spark plug works by creating a small, precise electrical spark at exactly the right moment to ignite the fuel and air mixture in the cylinder. When a plug is saturated in oil, that spark becomes weak and unreliable, and in some cases the plug fails to fire at all. The result is a misfire, where one or more cylinders are not burning fuel properly, and the engine runs rough as a consequence.

The oil was getting in through a failing valve cover gasket. This is a rubber seal that sits between the valve cover, the removable top section of the engine, and the engine head below it. Over time these gaskets harden and crack, and once they go, oil finds its way into places it should never be.

Leaving Oil in the Plug Wells Leads to a More Expensive Repair

A soaked spark plug is bad enough on its own, but the bigger concern is what happens if this is left. Each spark plug sits alongside an ignition coil, which is the component that generates the high voltage needed to fire the plug. Oil contamination attacks the coil's insulation over time, and once a coil fails you are replacing electrical components on top of everything else. A new ignition coil for this engine costs significantly more than a set of spark plugs and a gasket combined, so catching this early made a real difference to the overall bill. There is also a running efficiency angle here. An engine misfiring on one or more cylinders is burning fuel less efficiently, which means worse economy at the pump for every mile driven while the fault is left.

New Plugs Fitted and the Valve Cover Gasket Replaced to Stop the Leak at the Source

We replaced all the spark plugs with new ones to the correct specification for this engine and fitted a new valve cover gasket to seal the leak properly. The plug wells were cleaned out before reassembly so no residual oil was left sitting around the new components. Once everything was back together we ran the engine and road tested the car. The misfire had gone, the engine was pulling cleanly through the rev range and the hesitation on pull away had cleared completely.

If you are driving a Mazda or any other car and you notice a rough idle, a shudder at low revs, reduced power or a feeling that the engine is not quite running as it should, these are all signs worth getting checked before the problem develops further. An oil leak that seems minor can cause expensive knock on damage if it is reaching components it should not be near.

We carry out engine diagnostics, leak repairs and servicing at our garage in Walsall, and we are happy to take a look if something does not feel right. Book your car in with us at platinumvehicleservices.co.uk and we will give you a straight answer on what needs doing.