I've noticed my car is getting more and more difficult to start in the mornings or whenever the engine is cold. I'd turn the key and when it finally starts it'd run on 3 cylinders but by the time I get to the end of my road it's running sweet as a nut on all 4. So the first port of call was to check the plugs, figured I'd start with the easiest ones to get to. I pulled the plug on cylinder 1, it's looks ok, the gap is a little smallish but not wildly out. Gapped and cleaned it went back in. Pulled cylinder 4 plug, colour-wise the insulation was quite brown and the ceramic around the center electrode was cracked in three places and rattling around on it's own. Easy fix, just bang a new plug in, job done.
Took a stroll into town to find a replacement plug only to find no-one in Daventry stock Bosch spark plugs!! NGK only!! Hmmmmm.... I don't particularly fancy removing the black manifold and what looks like the injector bank just to swap two plugs. I bought a NGK plug that for some reason has 3 side electrodes whereas the Bosch ones only have 2. Anyways, I put it in and it has solved the starting problem.
Now the reason for this thread, the fella in the shop reckons you shouldn't mix NGK and Bosch plugs. Apparently due to "spark plug technology" they work differently. Now is he just trying to get me to buy more plugs or is he right?? In my mind the plug just causes the spark.
By the way, the car is running sweet as a nut at the mo with mixed plugs.