Hey, I was driving my 2007 cooper S (auto) today and came to a pretty steep hill about a mile long, going about 55-60mph. About a quarter of the way up I notice a miss, almost like the transmission tried to shift but didn't. Then, about halfway up the hill, the engine started shuddering/shaking and slowing down.



I made it up the hill and then a couple more miles down the road to a gas station. The engine felt fine unless I put it into 6th gear (I switched to manual mode) it would start shuddering again. When I pulled into the gas station and came to a stop the engine was shuddering pretty bad.



I just so happened to have my scan tool in the back, so I plugged it in and it showed these codes:

• 2A56 - Oxygen Sensor Heating After CAT Function
• 2777 - Combustion Misfire Cylinder 3
• 2D52 - DME Super Knocking
• 2DCD - Fuel Shutoff Due To Super Knocking in Cylinder 3
• 2781 - Combustion Misfire Several Cylinders
• 2771 - Combustion Misfire Cylinder 1
• 2775 - Combustion Misfire Cylinder 3
• 277D - Combustion Misfire Cylinder 2

I cleared the codes, switched the scanner to show misfires on each cylinder, started it, and it immediately would start misfiring, showing mainly cylinder 2 but 1 and 4 were also.



After sitting there for awhile, trying to figure out what to do, I decided to drive it back home.



I had the scanner on the misfire graph, and found that above 3,200 rpm there was no misfire, anything below that cylinder 4 would misfire like crazy, and if going really slow they were all pretty much misfiring.



When I got home I checked the codes again and it only showed these:

• 2781 - Combustion Misfire Several Cylinders
• 2775 - Combustion Misfire Cylinder 3
• 2771 - Combustion Misfire Cylinder 1
• 277D - Combustion Misfire Cylinder 2

I haven't done any investigation besides the codes. I don't really have any idea of where to start. Could be timing related, compression related, valve related, etc.



Any direction would be greatly appreciated. Thanks!

 

I would start with new coils and plugs, and see how it does after that. Sounds like the engine might have gotten a little hot going up the hill. Ignition coils don’t like heat.

 

N14 engine right? This bulletin is for the N12, but it applies to all N series engines. http://www.engineprofessional.com/TB/TB113017-1.pdf

You probably have valve seat or timing issues. Timing and valves are more likely to cause misfires in multiple cylinders.

Going up a long hill generates a lot of heat in the engine, and that's when valve seats in N series engines tend to drop. When they drop; it can be multiple valve seats dropping. In my latest case N12 engine, I had three seats drop the same time, but I had a hot idle misfire on cylinder 2 for some time. At higher RMPs the engine would not misfire. Here's what the seats look like when they drop.

Cyl 2

Cyl 3

Cyl 4

The N14 engine doesn't have Valvetronic as far as I know (somebody correct me if I'm wrong). So that's strange that your misfire would go away at higher RPMs (makes sense on a Valvetronic engine). With higher RPM, combustion chamber pressure increases, and if it's a secondary ignition problem the misfire condition will get worse not better.

What's next? #1. You need a compression and leak down test. That engine has 10:5/1 compression. The book spec for compression is the same as for an N12, 8-12 bar (or 116 PSI - 174 PSI with no more than 3 bar difference between the max an min cylinders (43 PSI).

If the compression check is bad, then perform the leak-down test to find out where the air is going.

Don't put any money into the car until you do these tests.

 

Thanks for the reply, I did put new spark plugs in, but that did not fix anything.

I then did a compression test...

 

No maintenance on that engine! Those plugs look horrible ... may be original. Need a leakdown test to see what the leak-down is for each cylinder and to find out where the air is leaking out.