So I had to recently change my lovely valve cover at 56k miles on my '11 MCS. Pretty ridiculous but that's besides the point. It's a pretty easy swap, but I managed to pop two codes. P0300-cylinder misfire detected and P0304-cylinder 4 misfire. I've been out of commission for the whole weekend since Friday because the car idles at 1k RPM's. I could barely drive it around the block. All temps(oil and water) look good, so no issues there.

I've done a bit of research, I see vacuum leak, spark plugs, and coils as possible problem. Kinda stumped what to do but thinking of towing it to Detroit Tuned and let them fix the issue. If anyone has any other ideas, please comment on. I've taken it off as requested by DT and unplugged and plugged everything back on. Thanks for any advice.

 

An easy way to see if a coil is the culprit, swap the one from cylinder 4 to another and see if the error message changes to reflect the new location (i.e. cyl.2)... If it does, then that coil is bad.

 

Well I forgot to mention, I did have cylinder #3 act up and switched the plugs with a different OEM one My buddy had laying around. It went away but then the other codes popped up.

I will give it a shot tonight. Thanks for the advice!

 

Just an educated guess....
Carbon buildup....number of miles? Ever been cleaned?
Try moving ignition coil....could be an issue, but beyond that Time to get it to a shop...
The misfire would closely resemble one of the main results of a severe carbon issue. Good luck!!

 

The engine speed might be getting raised because there is a misfire condition, not necessarily a vacuum leak. When I think about this more, BMW might know the engine has very harsh vibrations around 700rpm with a misfire condition, so they set the protection settings up in the ECU up to 1000rpm to be in a safe spot. Not guaranteeing anything but it's food for thought. Modern cars are complex!

It's hard to say if the high idle is vacuum related. The ECU is hyper sensitive to any air leaks so you would have seen P1497 for that error. Typically when a car has a vacuum leak at idle the engine speed will be bobbing up/down like it's hunting for the speed it wants to stay steady at. You could use carb cleaner to squirt suspect areas WHEN THE ENGINE IS COLDER (do this at your own risk). The engine speed will rise when you find the leak. I've only done this one time with my dad on my old Dakota. It's not exactly safe. However, the misfire issue seems to be the larger problem here.

Something to check that you actually have spark on the suspect cylinders is pull the coil and put the plug in it. Ground the threaded body of the plug and crank the engine over visually verifying you have spark. This is kind of a ghetto way of seeing if you have spark but it definitely works. I highly doubt it's a fuel injector issue at this point in the cars life. It's very possible a bad batch of gas clogged an injector. The R56 injectors operate at 1100+bar of pressure so they are very sensitive to sh1tty fuel. What really sucks is that they aren't exactly easy to access. If you've verified the spark is not the issue that would be another thing to check. If the issue follows the injector, you've found the problem.

The easier thing to check, besides spark, is compression in the cylinder. Like others have said, if carbon buildup has compromised the cylinder, it's very possible you may be loosing air on the compression stroke. The best way to check this would be doing a leak-down test.

Either way, the spark is the easiest thing to check. The fuel and air checks take a lot more time and specialized tools What you find during those test usually leaves your wallet crying

 

Some very good points if this just started with the valve cover swap....

 

So..I got a call from Detroit Tuned about two hours after I towed the car there, and when the swap was done, I didn't align the coils correctly on cylinder #3 and #4. So all in all, fixed even after I took it off a second time the other day haha. Glad that's over with. Lesson learned:-).

 

So now you can come to the picnic not on a flatbed!

 

Or a Challenger;-)

 

Carbon build-up is probably next. Pray the rosary!

 

ground wire is still in good shape that connects to the valve cover bolt ?

 

Rob...could you explain the "align" theory here. I still have my car apart and any little tip when I get ready to put t back together to avoid more issues would be great. thanks in advance

 

Okay so when putting your valve cover back on, prior to doing so, when putting the coils back on make sure they are aligned on the lip of the VC. It's as if you were looking inside to check your spark plugs and there's a lip you have to make sure the coils are on correctly. Otherwise the car will misfire like mine did. Just take your time when doing so, I learned for future reference how to do it if it happens again.

 

oh ok gotcha. they just aren't fully engaged then

 

Yep correct! It just needed to be adjusted that's all.