I have a bmw mini cooper s works and I have a hesitation at low rpm when I pull away from a junction it hesitates before accelerating I have noticed that cylinder 3 plug is sooty around the bottom and is slightly whiter in the mioddle than the other 3 cylinders these plugs where replaced approx 3 weeks ago with a cooler plug code 7 I belive I have put some injector cleaner through my fuel but this doesnt appear to have helped do you have any advice please thank you.
Are there any diagnostic codes saved in the computer's memory?
Hesitation upon starting from a standstill can be a few things. Check for vacuum leaks (but since you don't say it idles badly, I would rule this out). A sooty plug usually means that either oil is being burned or too much fuel for the amount of air. This could mean that the computer is telling the injector to stay open for too long, the intake valve isn't opening far enough to allow in enough air, r there are serious deposits on the valve that are causing the air and fuel to not mix properly while entering the combustion chamber.
Double check the plug gap. Pull the plug wires and check the resistance. They should be within a few percent of each other, otherwise, the voltage delivered to the plugs won't be the same. Lower voltage delivered to the plug will cause a cooler spark, resulting in soot deposit on the plug tip.