Cooper JCW misfire issue - best guess??

[cellieb]

Hello!

First of all, I apologise if this is in the wrong place, I've searched the forum and found several posts with the same theme as this but not necessarily specific to a JCW or my situation so I'm starting another one. If it should go somewhere else please move it

I recently bought a 55 plate JCW. It has FBMWSH culminating in an inspection 2 about 1750 miles ago before I bought the car. It has done 54,000 miles and is in great shape in all other respects.

I have noticed a misfire when the car is under load (say 50% throttle or more) in the higher gears. It only happens at low revs and seems to be more prominent the higher the gear. It doesn't do it in 1st and very very rarely in 2nd but in all other gears I can reproduce the misfire more or less at will between 2500 and 3500 rpm. Above that rpm no problem in any gear. Car pulls hard and I don't doubt it's using all the horses BMW gave her!

I know the regulars are all groaning by now but bare with me, I've done my homework honest!

There are no warning lights.
No leaks (air or fluid) that I can see.
Have poked the leads etc - nothing obviously lose.
Its not the ECU 1st gear thing that I read about.

I'm obviously hoping it's something really easy but the answers I've seen give such a varied list of potential suspects I am hoping someone can give me a place to start. I don't want to pay someone hours and hours of fault finding labour time and I don't really want to have to replace every component trying to guess the right one!

Spark plugs (shouldn't be as just replaced?)
Ignition Leads
Bypass Valve?
Coil Packs? (are there 2?)
Some random air hose
Injectors?

Has anyone solved this issue with any certainty? Sorry for being a pain in the rear first post

[bothor]

I would say coil pack.

I had this issue after some mods. If I opened the throttle right up between 2-3k revs it would misfire. Misfire may not be the right word - it would not spark and therefore make a sound just like when you let out the throttle and get engine burble. My mechanic swapped the coil pack and ignition leads and no problems since.

There is only one coil pack serving all four spark plugs on my 05 cooper S.

[kroiwi]

I am encountering the same problem.

I noticed once when doing about 105km in 6th, then put foot down (not past the click) and noticed a hesitation for a split second.

The other day noticed it in 4th gear when pulling onto the motorway, put my foot down as above and i could replicate the hesitation twice. Tried to do it again and couldn't.

Is there any way of servicing he coil packs? Saves buying a new ones..

Also the R56 has 4 coil packs, one per plug, which are not cheap to replace.

[Liam mini 35]

Did you buy the car from MINI? If so just take it back as the cherished cars have a 12 month warrenty.

[Eirik]

This is typical coli fault, buy one and try it on the different cylinders

[cellieb]

Thanks for the replies.

The R53 has one coil pack for all four cylinders - seems the R56 does not.

On the bright side it seems (touch wood) that I have got away lightly as a full tank of high octane fuel seems to have cured the problem. Either that or me taking wires off and wiggling them around a bit

I am nearly through that tank now so will be watching carefully for any relapses and will report back...