Intermittent Misfire - looking for a second opinion

Ryan Mechanic Middle Village, New York Posted   Latest   Edited  
2005 Mini Cooper S 1.6L (W11B16A) 6-spd (GA6F21WA)
P0304 - Cylinder 4 Misfire Detected
Cold Engine

Hello everyone, 

I'm hunting an intermittent missfire on this vehicle. We've been chasing this issue for quite some time. A while back we performed an induction service on the vehicle and the symptom failed to appear for a while but now it's back. Looking at the ignition pattern, this one stood out and I thought this scope pattern looked rich. Anyone have any thoughts?

Fuel trims look normal. 

Mario Diagnostician
Weston, Florida
Mario Default

So this is a waveform of the misfire? Would you happen to have a baseline waveform to compare it to. That waveform does not have a downward sloping burn line that usually accompanies a rich condition.

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Ryan Mechanic
Middle Village, New York
Ryan Default

I never actually feel a misfire, the client just started when cold, the light comes on. The car is very well maintained. I'vetried swapping parts around with no change. I was think either leaking injectors or some kind of carbon issue.

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Steven Mechanic
Spokane, Washington
Steven Default

The most common thing we find on these first generation Mini Coopers is the exhaust valves leak just slightly, so you get the intermittent misfire. A lot of times they don't misfire enough to set a code, but you can feel it run a little rough. You may be able to find it with a simple compression test. One or two cylinders will be low on compression.

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Tanner Instructor
Wellford, South Carolina
Tanner Default

Does the misfire only occur cold and go away when hot? Also what type of induction service was performed?

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Justin Technical Support Specialist
Fresno, California
Justin Default

Could you do a longer time base to create a parade pattern on the affected cylinder, or give multiple captures? I may have an idea with a few more complete captures.

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Felix Diagnostician
Miami, Florida
Felix Default

Check this out , is about the same problem , cold misfire

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Ryan Mechanic
Middle Village, New York
Ryan Default

It's port injection, however I did find Arab on carbon build up on the pistons. We did a basic chemical induction cleaning (through a vacuum port) and it seemed to help for approximately 6 months.

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Louis Diagnostician
Claremont, California
Louis Default

Hey Ryan. Keep in mind that some Mini Coopers will report the wrong cylinders misfiring. Your P0304, may actually be a P0301. I've chased a few misfires on the early models before I learned about this.

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