Please forgive me if this is a frequently repeated question. I have extremely little time for the next week, and this freaking Mini is about to give me an infarction.

I replaced the battery, which resolved my intermittent rough non-start issue, on Sunday. Monday, on my drive home from work, I started getting an intermittent misfire under acceleration--specifically under boost. This is a hard cut that comes and goes in a fraction of a second. What are common problems causing misfires like this on the R56?

2012 Mini Cooper S coupe, 65k miles, stock, driven daily on a 100 mile round trip commute that is virtually all freeway with lots of acceleration. Original ignition consumables.

 

I should add that there is no CEL currently and that I have not scanned because I don't have a scanner.

 

How do you know it is misfire?

get it scanned by autozone or ppbys even if the light is off.

if you accelerate gradually, would you have the same issue?>

 

When a power stroke is lost, that is a misfire. A misfire can have one or more of numerous causes. I am missing the occasional power stroke under load.

Accelerate gradually? I can't accelerate instantly. Do you mean accelerate at a slower rate? If so, no, it seems to be tied to boost.

I should also note that I have not yet detected a misfire with a cold engine. I first noticed it last night at the end of my 50 mile return commute from work. I could not detect a misfire this morning until I had reached the freeway. I can't say for sure that engine temp has anything to do with the problem, but that is the correlation I have observed so far.

 

yes, by gradual i meant a slower rate pressing on the gas. not sudden or semi flooring.

if power stroke is missing, wouldn't be a fuel injector issue then?

 

Triangle of fire. Lacking fuel, spark, or compressed air will equally cause the loss of a power stroke.

 

I am more suspicious of ignition than I am fuel. I would expect a misfire from an injector to be more persistent and not as apparently temperature dependent as my problem is.

 

Full tank of gas
remove and check spark plugs
check wire connectors to top of ignition coils
check your diverter valve and make sure the rubber lip is ok
with scan tool - you can check fuel pressure output from the intake pump and the HPFP.

 

Which scan tool should I buy? Carly?

If anybody in Columbus, Ohio has a little spare time to use a scan tool, that would be super. I'm surprised that this misfire hasn't thrown an engine light.

 

You said "original ignition consumables." Do you mean you're at 65K on the original plugs? They're due for replacement and could be the cause of your problems.

 

Correct. I don't mind replacing the plugs, but my second general rule of engine diagnostics is "its' not the plugs." That's right behind "it's not the thermostat." YMMV, but I have seen some pretty heinous looking spark plugs in my life on cars whose behavior didn't change even a little after replacement.

 

My neighbors camry has 130,000 on plugs and still runs great. My mini has a jcw sticker on the valve cover that says to replace spark plugs every 2nd oil change! But they also said the car only needed oil changes every 15k!

I stick to oil changes 4,000 miles and plugs every summer. The coils I did at 25k and again at 60k. A fresh battery every few years and the above and the car is reliable and much better to drive. Milage may vary, I average 29 mpg according to gauge and I drive it. Little trips, errands and long trips.

 

Damn. Replacing plugs every 20-30k miles was supposed to go out with points ignition and carburetors. This German car acts a little too British for my taste.

 

German owned made in Oxford.
Plugs are easy.
Swap them every 50k you should be fine....

 

Do you like the Brisk plugs or just OEM?

 

My 2011 MCS is doing what seems to be the same thing, I am at almost 80k miles. A big "jolt" of no power for a split second, then back to normal. Usually happens between 2500 and 3500 RPM's or so, and 80-100% throttle. Very intermittent! I change my plugs every 20k and use NGK Iridiums. These have maybe 10k on them. No CEL, no codes. I used this same scan tool to pull codes when I had a CEL and misfires previously when the HPFP was going out. This scan tool read all the misfire codes, as well as the fuel pressure codes at that time. Very interested to find out what the issue is with your ride, Longitudinal. Keep us/me posted, please!

 

Of course plugs are easy. 20k is absurd. That's my point.

 

What scan tool are you referring to?

My misfire has become significantly less intermittent in the last week. It now regularly stutters at anything more than half throttle and anything above let
s say 2000 RPM.

 

My German car experience tells me to start with the most expensive solution and work backward toward the cheapest. So I will start with the apparently trash ignition coils and add plugs. What brands of coil and plug should I seek out/avoid?

**EDIT** Oops, the most expensive appears to be the fuel pump. It's on back order at Autohaus. What is the best source for the fuel pump?

 

What is the preferred brand and source for coils and fuel pumps?

 

Is your neighbors Camry a TURBO !?

 

N O !!!!

By no means ever use them. Their ring seal does not compress at nm torque specs for the MINI and back out....Whatever the metallurgy they are made from is not proper for MINI.

Every person I have seen at the shop needing a helicoil and many in this forum has had them back out.....

Use OEM.

 

You asked for our help and those here have already explained your MINI is overdue for plugs and yet insist on spending $ on coils....

 

Plugs would be replaced with coils (invisible: "of course.") If I am reading correctly, plugs and coils have about the same life expectancy. It's inexcusable, but it appears to be the reality.

I'll ask again for the better choice in plug and coil.

 

Nobody gets a pass for a 25K plug change (let alone coils,) turbocharged, supercharged, or twin charged.