Hey everyone, new to the page and have a problem with a 2008 Mini Cooper base that we cannot figure out. Bought the car with the code for cylinder 1 misfire. Replaced all the spark plugs and coil packs. Replaced cylinder 1 fuel injector. Replaced several components of the evap system. Did a compression test on each cylinder and the all hold pressure. We clear all the codes, start her up, runs fine, then take her for a test drive. After doing all of this, the car begins to misfire again, at idle, only after driving it for about 3-5 miles. The CEL comes back on and the code for cylinder 1 misfire reappears. It seems like the misfire presents itself again only after the engine gets warm. We even did a compression test after driving her to see if it was loosing compression after heating up…it still has compression. Any suggestions or info would be of great help. Thanks

 

I’m in the same boat. Replaced plugs, coils, head gasket, and injectors. Cylinder 1 still misfires but only after driving for a while. I just discovered oil on the spark plug in that cylinder which isn’t a good sign.

 

Pull the plug for cylinder 1 and inspect it for oil both on the plug and in the well for that cylinder. When my misfire saga began I found the well for cylinder 1 full of oil which is why I replaced the valve cover gaskets. It didn’t actually resolve the damn issue but…

What compression readings are you getting? Mine were all consistent but very high. 225-235psi. That’s like a 15:1 compression ratio (it’s supposed to be 11:1) so I’m wondering if it’s indicative of a bigger problem or not. If only there was a repair/service manual that didn’t suck. I’d kill for a printed troubleshooting flowchart.

I was digging through related posts last night and found one where the OP said they resolved their misfire by replacing the PCV. They didn’t specify if it was the diaphragm or other components. Pelican Parts doesn’t have jack when you search for “PCV” and I reckon it’s because the diaphragm is considered to not be a replaceable part for some reason. Regardless it’s an easy and cheap swap so I ordered one from Jeff Bezos. At this point I feel like I’m just throwing parts at this car and it’s really annoying.

You may also want to clean your mass air flow sensor. It’s easy and a can is relatively inexpensive.

Anyway, that’s all I’ve got for today. I’ll be following along with your saga. Maybe if we combine our brains we can beat this. Also your post is newer so hopefully it gets some input. Mine seems to have fallen off the radar.

 

I’ve been getting 180-190 on all of the compression test for each cylinder. We’ve replaced the PCV diaphragm on the valve cover. Replaced all the valve cover gaskets as well.

 

Any oil on the spark plug?

 

No oil on the spark plug…when we swapped them out, the old one had quit a bit of carbon build up. I scoped the cylinders and #1 is full of carbon build up. I suspect that when the car “heats up” the carbon begins to glow cherry red and prematurely ignites the fuel when it get injected. Going to try and remove the carbon build up and see what happens. It would help to know that the previous owner did nothing to fix the misfire in the first place, hence all the carbon build up.

 

Ah, my old friend Denial.

 

Just replaced the PCV diaphragm.Man, they weren’t exaggerating about the likelihood of the clips shattering. Good thing the replacement came with a new cover. Will drive for a few days and report back.

 

Take it to an indy shop and ask for a misfire diagnostic, then change the part yourself. I had a similar problem ... intermittent misfire (cylinder 2). They found an intermittent fuel injector with a lab scope.

 

Replacing the PCV diaphragm had no effect.

 

Stop throwing parts at it. You need to have your intake valves walnut blasted clean, It's a direct injection engine and as such, fuel never passes over the intake valves to keep them clean, as it does in a traditional port injected engine. Three hours labor at your local MINI dealer, smooth strong power and no more misfires. Worked great for me at 85K miles.

 

Joe, according to the initial post, it's a base model with a N12 engine; it's not direct injected.

 

Finally got fed up and took the car to the dealership for a professional diagnosis. They boroscoped the cylinder and saw streaks of oil on the walls. They suspect the valves and valve guides are at fault but recommended replacing the engine as they said it’s cheaper than tearing it apart to rebuild. Quoted me $5000 labor plus parts but I stopped them and took my car back. Called a small local shop. Guy said he could do a cylinder head rebuild for about $3000 total but that it’s still possible the piston rings also need replacement which would raise the price considerably. At this mileage (84755) the Blue Book on this car is about equal to the repair quote so I’m going to start looking for a new vehicle and see what I can get for trade in. Bummer. I liked this little red roller skate.