Reasons for Obvious Misfire When Cold but Normal When Hot
2 Answers
There are many reasons for obvious misfire when cold but normal operation when hot. The following aspects can be checked: 1. Excessive spark plug gap. If the spark plug gap is too large or the electrodes are severely worn, it will result in insufficient ignition energy during cold starts, causing engine misfire. The solution is to replace the spark plugs. 2. Check the fuel filter and fuel pump. During cold starts, the low temperature causes lower oil viscosity, and if the fuel filter is clogged, it leads to an overly lean air-fuel mixture, causing engine shaking similar to misfire. The solution is to first replace the fuel filter; if the issue persists, the fuel pump may need replacement. 3. Clogged fuel injectors, commonly seen in direct injection engines. In direct injection engines, the injectors extend directly into the combustion chamber, so carbon deposits from combustion can accumulate on the injector nozzles, leading to clogging. The solution is to replace the fuel injectors.
The engine shakes violently when starting cold, but runs smoothly when warmed up. This is a common issue I encounter. It could be due to aging spark plugs, which have low ignition efficiency when cold, causing misfires in a cylinder. Alternatively, the ignition coil may perform poorly at low temperatures, leading to unstable current supply and cylinder misfires. Once the engine warms up and components operate normally, the issue disappears. When I repaired my own car, replacing the spark plugs worked well. If that doesn't help, check for carbon buildup—clogged intake ports can worsen the problem. Regular maintenance with fuel additives to clean the injectors can reduce such issues. Don't underestimate it; prolonged buildup leads to costlier repairs.
