.....Or not such an interesting question. I went to the subject vehicle with a misfire on number 3 cylinder (3 cylinder model). The owner had replaced plugs, coil and injector on No 3 cylinder to cure misfire code P303 but to no avail. The vehicle also drops into limp when the EML illuminates. Now the archives are awash with this subject so I was well prepared with an insight to the problem. For those not in the know, it is caused by an engine problem normally burnt or poor seating valves and the management system will switch off the injector to the affected cylinder.

My question is this: How does the ECU know that there is a mechanical problem with the affected cylinder? Archives point in the general direction of the crank sensor but I would like to know if this is so and how can the sensor determine a misfire on a particular cylinder?

I would be grateful for enlightenment.

Regards

Pete M