Smoking and misfiring

After it has been warmed up, my Peugeot 306 1.9 TD occasionally starts smoking and misfiring. If I leave it to cool down, it’s fine again. It will sometimes drive fine when warm. The level in the radiator is steady, with no signs of oil contamination, and the oil level is OK, with no traces of water. Could it be fuel contamination? The fuel filter was changed recently. David James

You say that the fuel filter was changed, but do not say if this problem happened immediately after the change of filter or occurred earlier. The symptoms do not sound like fuel contamination, as this would not normally be temperature-dependent. You do not mention the year of your Peugeot or the mileage, but being a 1.9 TD I am assuming it dates from 1998-1999.

As you have checked for any cross contamination between the oil and waterways without finding any tell-tale signs of head gasket failure, this can hopefully be dismissed, although it may still be a possibility. My first check would be to the fuel system, ensuring that there are no leaks in any of the fuel pipes or fuel leak-off pipes. According to my data, your Peugeot may have either a Bosch or a Lucas injection system. The problem may be a faulty or sticky injector, so providing no problems can be found in the fuel lines, try using an injector cleaner in the fuel tank before taking any further action.