Intermittent Misfire - looking for a second opinion

Ryan Mechanic New York Posted   Latest   Edited  
Unsolved
Driveability
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. 

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Mario Diagnostician
Florida
Mario
 

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
New York
Ryan
 

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
Washington
Steven
 

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
South Carolina
Tanner
 

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
California
Justin
   

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
Florida
Felix
   

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

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Ryan Mechanic
New York
Ryan
   

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
California
Louis
 

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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