Number 2 cylinder fault

Q My son has a 2010 Vauxhall Astra SRI. For the last two weeks, when it’s in use and with the engine warm, the warning lights – engine management, a spanner shape on a car – are displayed. There’s a fault code stored relating to ‘number 2 cylinder fault’ and a cracked spark plug was apparently to blame. All was well for four days, but now the problem is recurring intermittently; if you turn off the engine and restart, it disappears for a while. We’ve also noticed that the fault develops more quickly when there is a need for power.

My local garage says it could be either the injector on that cylinder or an exhaust valve fault. I have also been told it could be a coil pack issue. On fitting a diagnostic tool, for the first three to four attempts it does not show anything, then on a fifth attempt it shows ‘number 2 cylinder fault’. T Roberts

A You do not mention the mileage of the vehicle, but the most likely candidate would be the coil pack. Sometimes a damaged spark plug can cause failure of the coil pack due to the incorrect resistance of the circuit. The failure of the coil pack would tie in with it breaking down under load.

If the fault was due to an exhaust valve, I would expect to hear a popping from the exhaust on tickover, and this should be detectable using a compression tester. While the fault may be due to a failed injector, this is less likely.