During the ongoing problem that I have with my 1994 2.0i petrol turbo estate I put in some new spark plugs.

Since then I have only driven it about 20-50 miles.

I removed the plugs to see if they could tell me anything about the state of the engine management.

I noticed that the white insulation around the centre electrodes on cylinders 1 and 2 were like new but on cylinders 3 and 4 they were slightly grey.

I'm not a car mechanic, but the uncannily clean insulators seem suspect.

Has anyone experienced this before or suggest a reason for it?

Many thanks