Driving home tonight in the 08 justa with 88000 miles and suddenly get misfire code cyl #1 and p137 o2 sensor code. Seemed to be running OK until we got home and then we could tell it was running rough. Will a bad o2 sensor cause the #1 misfire or is it the other way around? How much work is changing the spark plugs? I can't even see where they are! This is what I get for bragging up our 88k mile justa in the reliability thread the other day! Also is the bosch 15379 the right sensor for this car (after cat) ?

 

What was the EXACT misfire code?

* MINI DTC P0137 - O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)

With the fault code above, the post-cat O2 sensor is seeing a low voltage issue.
That could either mean a dying sensor or frayed / exposed wiring.
However, the post-cat O2 sensor does not affect fuel trim adjustments; the post-cat only checks sanity of the catalyst.
So to answer, NO, the O2 sensor is not creating a misfire; you have two different issues.

Very easy; remove the ignition coil cover (if a Justa), remove the ignition coil on the cylinder and insert a spark plug socket into the hole.

You need to cross-reference with Bosch directly.

- Erik

 

its a cylinder #1 misfire p301 I believe. If the sensor didn't affect the spark could the lack of spark mess up the sensor?

 

* MINI DTC P0301 - Cylinder 1 Misfire Detected

No. If lack of combustion was making the catalyst overwork, you'd see a "Catalyst Efficiency Below Threshold" fault code.

- Erik

 

so do you think I need a new sensor considering the mileage. Also I have never changed plugs and I'm not sure if they were changed under the factory maintenance plan. So i'm assuming it could use them. Have never had any check engine lights before and these codes came in together, so what do you think?

 

O2 sensors do fail when they've been subjected to abuse or excessive air / fuel mixtures for long periods of time.
Some O2 sensors just randomly die out over time; I've had that happen to myself personally on a different vehicle.
But I wouldn't start with a replacement; clear the code and see if it independently returns.

I can almost guarantee they have not been changed as they are "suppose" to last some 100K miles on the Justa's; every 60K miles on the 'S'-models.

To verify it's NOT an ignition coil, swap the affected cylinder coil with another cylinder, clear codes and drive.
If the CEL returns and the fault code reports that now the swapped cylinder is now misfiring, it's the coil.
If the CEL returns and the fault code reports still cylinder #1, replace the plugs.

- Erik

 

Sounds like a plan, I have a code reader and did clear the code and started the car and it ran rough and the codes came right back. Tried this a couple of times with the same results. Thanks for your help it is really appreciated. I will try changing the coil packs and see if it follows it. Are they expensive?

 

They range from about $5x.xx each or so.

- Erik

 

Swapping them around is a lot cheaper than replacing them at random. Try changing them around as was suggested by Erik (Bluefox). Make sure that you've got a bad part before just throwing money at it.

 

Well I pulled plugs this am and the #1 plug had a gap big enough to walk through so I regapped all the plus and put them back in and still got the #1 misfire code. So I swapped plug 1 for plug 3 and still got the code on #1. Then I switched coil packs and the code followed the coil pack. So the local Advance has it in stock but finding new plugs for this thing is a most impossible I'm finding out. They look it up and bring out some standard plugs that aren't even close to those long skinny Berus! Mini wants $25 each for them and supposedly a Denso 3461 will work but can't find them either. Found the densos for $16 each on eBay though. Anybody else have trouble finding plugs?

 

Soooo...the coil pack Advance had was the wrong one just like the spark plugs (imagine that). It seems that according to ALL part store books and computers the the Justa takes standard $3 plugs and a 4 to 1 coil pack, even though that's not so. According to all of them it is the Cooper S that takes the fancy skinny plugs and individual coil packs. I spent half the day on the phone trying to track down the right plugs and a single coil pack (for an S) and NOBODY can get them except the Mini dealer. So I drove the hour to the dealer in Knoxville and bought the coil pack for $80 and I found the Denso 3461 plugs on eBay for $48 for four. The dealer wanted $26 each for the Beru plugs, I passed on them. The misfire code is now gone, I regapped the old plugs until eBay delivers and the car runs better than it has in awhile. Not sure why but the bad coil pack caused the gap on that plug to be huge, the electrode is basically gone. Sure is easy to change those plugs though, Thanks for the help.

 

The electrode wears out due to electrical arcing; it has nothing to do with the coil causing the spark to wear out.
But the large gap spark more than likely caused the coil to fail as it's required power to spark across a bigger gap significantly increases.
Glad you found out the issue.

You couldn't locate a Beru 12ZR6SP03 [NGK PLZKBR7AG (#5843)] locally for your Justa? I'm surprised.

- Erik

 

I live in very rural SE Tennessee, after all morning on the phone I finally found one guy that had ever heard of one of those plugs. An hour north or south gets you Knoxville or Chattanooga but here in McMinn County its a different planet! Hillbillies were invented here. These are my people......this is where I come from...on that red dirt road...and so on!