though the application is a non-turbo it does still fall under the highest compression ratio in a mini cooper. Or at least I think it is at 11to 1 compression ratio. Meaning that it stands a chance of detonating in the combustion chamber more times then not. In perspective 13 to 1 your pretty much using Airplane fuel.
Misfires can be something like a pvc breather hose. They tend to crack if they are the original more times than not. And the re vision is better then the older version of PVC but the lock collars break easier. WILD!
In some situations you have to cut that sleeving back on the PVC to inspect the entire hard plastic PVC line.
Catalytic convertor can do it. Someone brought a Oxygen sensor. Though it was literally the first time I ever heard that was the fix.
Oxygen sensors I have stood by over the years they are double robust for the application in the Mini Coopers in my opinion. It's the catalytic convertor itself that tends to go out first. And the O2 sensors are still good to go after.
So I will say from the other testimony I just read about the chances of the O2 failing is 10 percent chance.
the knock sensor. they are cheap enough. Crank sensors are cheap enough also. You could probably get both those
sensors for under 70 dollars U.S. after shipping.
But that is not how I have seen stuff get solved with these little gems called the mini Cooper.
Misfire is old spark plugs in some cases.
These spark plug are application specific for the non turbo mini cooper and will not work on the forced induction types in the second gen cars.
View attachment 280012
This is one of those parts where I look at it with a forced induction car and am jealous. That has been my take on the non turbo versions of mini cooper. They have there specific aftermarket parts.
Another thing you can look into is something like
Using Super Lube Silicone Grease during installation helps protect an O-Ring from damage by abrasion, pinching, or cutting. View our O-Ring Silicone Grease selection.
www.super-lube.com
And take the valve cover off the engine; is what I would do(it's easy enough). Then just wipe the valve cover gaskets off and apply with two fingers in with lube and the other hand holding the gaskets and wipe O-ring silicone grease. IF I needed to know for a fact I don't want a air leak I would even wipe a thin coat of O ring grease on the intake pipes before band clamping them down. If that's the case.
I would use it on the intake manifold if I remove it on the O ring gaskets there also. Air tight means air tight.
The gaskets around the spark plugs tend to create all kinds of leaks oil leaks included; in between the valve cover and cylinder head. O ring grease is easy and takes care of all the outer perimeter gaskets for the engine. Unless the rubber O rings are too far gone! But they make that brand new hermetic seal.
I would buy One new coil and swap it out between all four cylinders before deciding which coil to pull out of the engine. After I would find that one weak coil and pull it out that cylinder I pull it from most of the time is not gonna have the good graces to have that new coil on it. I will then swap another old coil and put that on it. Favoring the number 2 cylinder in my car. Most of the time the 4 cylinder is the one creating the problem in mine, but the point is not to directly replace the weak coil cylinder it came from with a new unless it will not quit misfiring unless you do.
The reason why I am spending time talking about 1 Coil in a 4 mis fire situation as this thread is talking about. Is because Seems to me sometimes 1 coil can wake up the entire coil system and clear up all the misfires. Because a new coil reduces the electrical load and increases the grounding to the engine block. There fore If I did buy a new coil and swap a old one out. I would keep the old coil. For years to come or until I could put in back in the car in multiple situations to verify it is in fact dead.
One coil saves money then buying a set of coils for three hundred dollars U.S. when On is about 45 dollars. And the rest of that money can go to fix the problem if that does not. Meaning The vanos solenoid being clogged up and requiring a new one. Or a PVC Breather hose that lead to the Intake Manifold.