Question about running rich?

[silviaz]

I was curious, not for any car in particular but a general question. If a car is running rich due to a faulty fuel injector for example it would be only one spark plug that would be dry and black correct? But if it's something like a failed oxygen sensor or fuel pressure regulator would all the spark plugs be dry and black?

[Duncan]

Yeah, pretty much. If the issue is in 1 cylinder you'll only see it on one plug (one injector or one coil pack), but if it is general like fuel pressure, bad tune etc you will see it over all. Failed o2 sensor not necessarily so simple because they only normally are used at light/constant throttle

[silviaz]

53 minutes ago, Duncan said:

Yeah, pretty much. If the issue is in 1 cylinder you'll only see it on one plug (one injector or one coil pack), but if it is general like fuel pressure, bad tune etc you will see it over all. Failed o2 sensor not necessarily so simple because they only normally are used at light/constant throttle

Ah ok makes sense. Cheers