Hi everyone, I read this forum all the time, although this is my first time posting, and thanks for all the help in the past

A few days ago my mini started acting up. I was on my way to work when the engine became louder than usual. I would describe it as sounding almost like a lawn mower. This sound seems to be present until I reach an rpm above 2500, wether I am in gear or not. I am experiencing some hesitation to go (especially noticeable in lower gears) and I can feel prominent vibration when I accelerate. When I am sitting still and in neutral, the car is shaking. The only code pulled (at autozone) was "P0303", a misfire in cylinder 3. I removed the spark plug to inspect it. It looks fine, but a little wet. (Note: I pulled the 3rd spark plug from the left. Also, mechanic cleaned out some carbon buildup in my exhaust about two months ago. I have had no issues up until this one.)

Any help and/or suggestions as to what I might check next is muuuuch appreciated.
Thank you,
Allison

 

The typical carbon buildup in these cars is in the intake. Is that what was done, or was it the exhaust that was cleaned?

The lawn-mower sound makes me think exhaust leak. If there was work done to the exhaust, it may have disturbed a joint or some such that is now leaking. Or maybe a compression leak, where the stuff inside the combustion chamber is leaking out.

The wet plug hints that oil, coolant, or lots of unburned fuel is getting into the combustion chamber. Your nose will tell you if it's unburned fuel; it may tell you if it's coolant.

Assuming the carbon cleaning was really in the intake, the latter two points are making me wonder if the head gasket is OK... Try a compression test, it will show up any compression leaks. And check the exhaust for any sweet smell of coolant.

 

Oh--I should point out that not all scenarios are doom and gloom. The exhaust leak could be something as simple as a wastegate that sometimes sticks open. Though I think you'd get a CEL for that.

 

I appreciate your reply! I will be doing a compression test ASAP. I have rented the tool from Autozone and am waiting on a friend of mine to help make sure I don't mess anything up. I have a bit more info also, the whole motor shakes when the car is idling. I think a lot of the sound is something the motor is rattling, but I can hear bad sounds coming from under the car near the backseats? Like I said, I'll have the compression readings soon. And I appreciate the detailed response

 

Oh, and I'm about to sound stupid probably, but I'm not sure which he cleaned. It was on the side of the motor that is closest to the windshield.

 

I don't understand what you're talking about, what is closest to the windshield? Are you talking about the intake manifold? It would be black.

 

Exhaust manifold is on the front of the motor, so it sounds like intake was cleaned.
Timing chain ever been replaced?

 

Thank you, it must have been. It was replaced not too long ago. Apparently the tensioners broke and they replaced the belt and tensioners. I'm not sure what else they replaced, though. A friend of mine says minis have a problem with the chain guard breaking and causing some similar symptoms to what I am experiencing.

 

Does your climate have a lot of moisture in the air? That might account for the wet spark plugs.

The chain guards break because the tensioner didn't properly tension the timing chain creating slack, after a while the chain stretches to a point where it starts hitting the upper chain guard and can sometimes come off the cam sprocket destroying the engine. My chain guard had pieces of plastic that had broken off and fell into the oil pan, that's not good because it can clog up the oil siphon or pickup where it draws oil from the bottom of oil pan.

You mentioned they replaced the belt, I'm wondering if their talking about the serpentine belt that turns off the crankshaft giving the alternator, AC compressor the power to operate. My worry is that in your case they only replaced the tensioner and not the chain guards and actual timing chain, once it's stretched it will fail at some point. You need to find out if your entire timing chain and guides were ever replaced.

 

I'm sorry I meant to say chain, not belt. I will look at my service receipt from that visit to see what parts they actually replaced. Thanks for the input, I hope to figure this out soon!

 

Oh and I do not live in a wet climate, I live in Fort Worth, TX lol

 

By the look of that one plug I would say its not firing much if at all on that one. compression test will tell you a lot!

 

To do a compression test, what do I have to disconnect first? An were is anything located (fuses, etc)? I couldn't find a fuse listing for r56 coopers, only the gen. before it.

 

Did you check to see of the ignition coils are OK? It happened to me and a couple of other members here... The easiest way to check is to swap them and see if the misfire error code changes cylinder. If it does that is your problem and you just have to replace the faulty one.

To remove them, just lift the connection clip, it will eject the connector and pull the coil upwards. The Delphi ones (OEM) tend to rust and are difficult to remove. I replaced with the Bosch alternative, as used on BMW engines, which is completely encapsulated in rubber, will not rust and removes easily.

 

The coil is bad! I haven't yet replaced it. I can't believe I was thinking so many horrible things could be wrong with it. I'll post again once it's replaced and let you guys know if it is completely fixed afterwards. Thanks for all your help!

 

I'm surprised it took 14 posts before someone mentioned the very first step in misfire diagnosis, move the coil to another cyl to see if the miss moves. my cyl 4 coil went bad last week. felt a hesitation while on boost, after that jerk it would only miss after 2500 rpms, 15min later it constantly missed even at idle.