I wonder if anyone could offer some advice. I'll try not to be too vague
I have a 2003 Cooper, with some mild mods (Miltek cat-back and K&N 57i) which have been in place for over a year. The car has done 137k and has never had any running probs, and still pulls (pulled) strongly.
It went in for a service 6 weeks ago and apparently a cylinder 1 misfire code was logged in the memory, however I never noticed it. They checked the valve springs and they were ok, so they replaced the leads and plugs.
After 2 weeks, a tapping noise apeared on #1 which then developed into a misfire. I took the car back. They said there was a fault with the lead and the noise I could hear was the spark arcing. They fixed it and the noise has gone. However, as I found out on the way home, the misfire hasn't.
Power is noticably down (feels like I have 4 people in the car), the car sounds and feels 'wrong' and after 10-20 mins of driving I get an intermittent and very noticable misfire, normally when pulling away, so the car coughs, splutters and burbles and won't clear.
I've read a few posts in forums, one of which hints to the ECU shutting down the injectors when it detects a misfire, so that might account for my lack of power, but I'm drawign a blank on what is causing the misfire problem.
The fact that it takes a while to become apparent must be of significance as the engine has warmed up by then. I have considered various sensors including water temp sensor, but I'm sure all of these would appear as a fault code if they had issues. I'm also guessing (hoping) that it's nothing valve / spring related as this would cause a constant misfire, rather than a random one. Odd that it's all centred around #1 pot.
The leads are normal replacment items, but I have considered upgrading to Magnecors and an MSD coil pack. It's had a new ECU by the way, a couple of years back so I'm assuming that's not the fault.
Anyone got any ideas?