Modern engines rely on a raft of sensors to inform the computer of what’s going on under the bonnet and what needs to be adjusted to keep the thing running smoothly and efficiently. A car that is using too much fuel and stalling could be having a problem with the sensor that tells the on-board computer that the engine is up to operating temperature. A cold engine needs more fuel to run properly so, if the sensor is telling the computer that the engine is still cold, the computer will continue to inject extra fuel into it. Of course, if the engine is up to temperature (regardless of what the sensor says) that extra fuel will show up as increased fuel consumption and could easily make the engine stall or run roughly.

However, that’s just one possibility and with the dozens of sensors dotted around a modern engine, the best advice is to have the car electronically scanned to see what fault codes are thrown up. The good news is that these sensors are usually inexpensive to replace and should return things to spot on pretty much immediately. Other suspects would be oxygen sensors and maybe even the stepper motor which controls the idle speed.

If there is a sudden loss of power, as you describe, I would be looking for an electrical fault, perhaps a faulty sensor, such as the crank angle sensor.

NISSAN service specialist Jerry Newman says he has never had a problem with the N15 cylinder head cracking, and reckons the $3500 cost to replace it is high. Because it has happened again so soon after replacing the head, and assuming the people who fitted the replacement head are reputable, I would look further for the cause of your problem. Consider a sticking thermostat, a leaking radiator or hoses, or incorrect coolant.