Voltage given to the spark plug in a petrol engine?

Answer 1

This depends on a lot of variables. If it is a older vehicle with the old fashion type ignition coil and breaker points in the distributor, about 30,000 volts. Electronic ignition, or distributor-less ignition, around 40,000 volts. If using a "Blaster" type coil from MSD then it's around 48,000 volts.

This voltage cannot be measured with a conventional volt meter and you should NOT attempt to do so. A high voltage probe would do the job but the interval between discharges will probably cause the indicator to read somewhat less than full voltage simply because the needle would not have time to reach the proper indication before the voltage when away.

Instead of trying to measure the voltage I always either use an old but still pretty good plug on the end of the wire making SURE it is grounded on the outside of the plug. DO NOT touch it or you will get a severe shock. Alternatively you can remove the plug wire from the plug and insert a small screwdriver blade into the wire's plug clip and lay the screwdriver down so the metal part of it's blade is touching metal (ground) and then start the engine. If you see a nice blue spark then you are alright. If however you only see a yellow or reddish colored spark that is considered a weak spark.

As you can imagine, doing this in a dimly lit place is best so you can see the resulting spark without being blinded by daylight.

Never pull a plug wire while the engine is running.