Okay I have a 2006 Mini Cooper s. Recently made a trip 5 hours away and got home went to bed next morning the car started on a misfire. It was a cold day so I thought nothing of it. Now it misfires when it's not warmed up and when I give it a good amount of gas. So I did what any other person would do, I read the codes and got "cylinder 4 misfire" I then bought new plugs, plug wires, installed an msd ignition coil, installed new cylinder 4 injector, opened the valve cover (saw nothing bad), I have a boost gauge installed so I bought new vacuum lines and redid them. I bought new inter cooler boots, and map sensor too. Still got the misfire cylinder four. So I then went out and bought a compression test all of them read around 145 psi which I asked a local dealer and they said its fine. So my burnt valve was out. I gave up and took it to mini. They charged me an arm and a leg to tell me that they did the same thing as I did above and don't know what's wrong. The only thing they did was a leak down test and said it passed. So at this point I'm out of ideas and the only idea I have is the BPV because I have read online about a yoyo effect and I think I'm getting it. But I also zip tied the thing shut and I got a misfire again. So any help I would really appreciate, thanks.

 

You have covered the things I would have tried. Do you have software that can read the "freeze frame" data stored with the code?

Check your map and t-map sensors. Mine got oily once and the bogus readings caused all sorts of fits. After that, I would try clearing adaptations and then a smoke test for a vacuum leak.

My car ran worse with the msd coil. If it's not bad, I suggest going back to stock.

 

Alright I will switch back to old coil see if it does something. Pretty sure the dealership did that too. What's the easiest way to smoke test?

 

Possible causes of P0304 from OBD Trouble Codes:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

 

Mine runs fine with MSD coil. Make sure there are no leaks anywhere at intercooler boots.

 

Going on trips you never know what kind of gas you're going to get. Double check your fuel filter to make sure it's not clogged as that could be causing misfires too, especially if you've replaced everything else.
If it is, make sure to use Seafoam/Marvel Mystery oil to clean out your fuel lines as the dirt could be spread to your new setup and still be causing misfires.

 

I don't think it's your BPV. You've done a good job chasing the common causes of a cyl. 4 misfire: a logical progression. Just for giggles, do a couple of things that won't cost you money, like swapping plugs and wires from cylinder-to-cylinder. It's probably nothing, but it's free and easy. Also, did you make sure that you had a good o ring on that new injector? A smoke test might be of help but I'm not super optimistic that a leak is your issue. I feel like you should step backwards and re-tests what you've already tested. Good luck.

 

I am running a straight header with no cats, so maybe the o2 sensor is dirty?

 

This is key information to supply with your original question. It is not a surprise that a cat-less header causes post-cat O2 sensors codes. That O2 sensor is essentially checking the health of the cat, which isn't there!

I am curious - was MINI willing to work on the car like that? They usually insist on putting it back to stock.

Is it still running rough or is it just an error code problem now?

 

Seriously, check your fuel filter man.

 

They never mentioned anything about my Catless exhaust, I was surprised myself. Didn't get around to the mini with this 36 inches of snow but will try some stuff today.