Before I list the details:
Could a clogged cat cause misfires and fouled plugs?

I have a rough idle and after clearing those codes and restarting, I'll get the P0300 Random Misfire and assorted cylinder misfires.

Swapping plugs & coils didn't change that.
Clean plugs made the misfiring etc, more pronounced.

The top o2 sensor was black, I read the live data while it's idling and it's reading fine, though I had a spare and replaced it, to no Avail...
Second o2 was okay, till recently, I used a simulator to bypass it (cleared codes as well) though the misfires have continued.
So I'm thinking it may be a clogged cat leading to too much backpressure?

Fuses are Good Relays Check out.

I'm getting that unburnt gas smell and the cat may be fouled, could it being fouled or clogged, cause the misfiring?

I'm about to try a catless down pipe but I'd like to know of anyone else's experiences, dealer fixes, diy advice etc!

I've read about 50 threads from multiple forums and tried everything, extensively, electrical, mechanical, but plugs are still being fouled... But please leave any positive advice or experience I'll try it and report back. I could make a video & most likely will, anything to
Help You Help Me A

 

Do you have a boost gauge installed in the vehicle, or the ability to get your hands on a mechanical boost gauge that you can t into a vac source to monitor how much boost your car is making? Usually if your cat is clogged weather it be partially or fully causing back pressure, your vehicle will have trouble making boost (proper amounts or set amount). Your car would also exhibit a very sluggish feeling @ WOT, like the car is very underpowered.

From what you've stated (symptoms wise), have you looked @ your intake runners recently for possible Carbon Deposits on the backs side of your intake valves? It may be that your car has a heavy build up of Carbon Deposits on your Intake Valves causing your rough Idle, as well as misfires. I would start there, and if you see an excessive amount of build up on the valve stem and guides as well as seats of your intake valves I would def. perform Carbon Cleaning. The rich smell you are smelling may be caused from this issue as well. Try with the vehicle in neutral and semi cold, rev it hard on and off and have someone view the exhaust. If you get a good amount of black soot, it could def. be carbon build up.

Make a video, as it would help me better see, as well as hear what your engine as well as how your idle seems to appear.

Oh I wanted to ask, who pulled your codes for misfires? Were there any faults for knock, or super knock? As for my experience, I work for and on MINI's all day, everyday.

 

Thanks, that really helped confirm my suspicions
I have a boost gauge and I'm
Low on boost + wot sounds almost rev limited/governed! It can barely rev out, unless it's feathered slowly, sometimes it just hangs at 5000, which I believe is caused by the code.

I'll Definetely recheck the valves, though I did a seafoam treament recently, since it's been pushed on, also it's been driven on this rich condition for some time. It's just rolled over 10k km.
The seafoam cleaned out some carbon, as it blew it through the exhaust (on to a towel)

Recently, after idle, while running rich, it's been spitting out lil black specks as well, much like after the seafoam treatment. It's definitely sludge and fuel.

I pulled the codes with an autologic scan tool as well as with my dealer level bmw tool (I have quite a few bmws, so I've stayed on top of the tools+diagnostic equipment I'd need)
No knock, though with the rough idle, once the revs were really low, before it stalled, it made a literal knocking sound from the valve/cylinder head area, which was.

There are only misfire codes, at the moment, though Ill post any sporadic codes that may arise.

Thank You

 

I hate to tell you this, but i bet when you performed your CC cleaning (via use of seafoam) you got allot of the Carbon (which ended up becoming fuel soaked) Deposits caught up in your cat which is causing your back pressure issue as exhaust is unable to flow properly through the cat. MINI & BMWNA perform a Walnut shell blasting technique to remove Carbon Build up from your intake runners, and in this process they vacuum the walnut shells as well as the carbon that is being blasted off VS. allowing the broken off carbon/oil/fuel to pass through the exhaust system which can cause issues like you are seeing. You stated your still seeing small amounts of it burning off even now. There is no real way to clean your cat, but I could recommend that if you could get your hands on a test pipe and aftermarket down pipe that are catless (basicly eliminate the cats) you would def know if your cats are the cause of your issues.

 

No. If you're seeing a misfire, that's typically cause from failed electrical (plugs / ignition coils) components.
That's especially true when the CEL is flashing; that means the ECU has detected a serious electrical misfire.

What plugs were used? Did you set the proper electrode gap?

No, clogged catalysts occur, but that occurs in extreme conditions.
If you just started having issues with a misfire, the catalyst isn't "clogged"...
You've got an engine issues, not a clogged exhaust problem.

How quickly are they fouling out? Have you completed any data-logs with an approved scanner?

- Erik

 

Okay, I'm now thinking the problem may be:
Electrical cause by Coil failure, they receiving the proper signal and the plugs spark when the motor is turned over.
with further hinderance
Mechanically from the coated/clogged cat, which I'll check tomorrow morning.

Tomm I'll put on one of my catless downpipes.
The plugs were gapped, but I'm gonna pickup some stock plugs from the dealer just to be sure it's as close to where it should be as possible.
(I have a few sets of the Denso equivalent as well as the next range up and down.)

The CEL once cleared, always reappears shortly after starting, along with a steady misfire that causes a stumble when you try to rev up.
It wont appear right away if you keep the idle slightly higher (so the ecu isn't "idling") though the misfire is evident from the sound emitted.
As soon as the car is allowed to idle on its own, it builds up a rough tone that sets the CEL.

@Boost_Spike: I knew the Seafoam could cause that, but I tried it first as one of the "last resort" measures. I really couldn't pull the head off!
I have a few catless downpipes from a previous build that'll allow me an alternative in case it is the cat.

If I put clear & clean plugs in, start and rev the car for about 30s-1min, then pull the plugs, they will be coated/black.
I didn't specifically set out to test that, but I had pulled the new plugs out right after putting them in and thats what I found. I'll test that properly, tomorrow.

From the datalogs and observation of data, the coils are being controlled and signalled correctly, therefore this missing could be from them, so I will get new coils as well.

This has been going on for a while, so when I pull the downpipe, I'm pretty sure it'll be heavily coated. I'll take photos for sure! I have some photos of the plugs, which I'll upload as well.

@BlueFox280: I remember your Photography from a while ago, I'm a photographer as well

Thank You Again, Let me know what you think!
You've been of Great Help

 

What was your outcome here?

 

Bumping this thread and PM'ing the OP as I'm having the EXACT same issue and no one seems to have any ideas what could be the issue.... HPFP checks out (per fuel rail pressure), injectors are cleaned, I can't imagine it being 1 plug or coil as it's a consistent all-four cylinder misfire issue, compression check checked out good, and it was a SUDDEN issue. Was driving along when all of the sudden it started doing exactly what the OP has described here.

Would LOVE to know what his outcome was.

 

Has anyone else had these issues????? I'm having the exact same issues as the OP and have no help. These things have been out since 2007 and this is a forum full of enthusiasts and I have never had a harder time finding help with an issue on a car. Forums are usually my first stop when I can't figure an issue and it's usually quick and easy to find multiple people with answer but this issue is kicking my ***.

My codes are all the same. Each time I reset the codes with Torque and fire the car up again and read new codes.
-P0301,02,03,04 (misfire on cylinder's 1 through 4)
-P0300 (Random Multiple Misfire)
-B2AAA (I've all but given up on this one. No one on all of the internet seem to have a single ****ing answer to what the hell this mystery code is).

-Clean valves did nothing.
-Removed, disassembled and inspected every inch of the intake manifold and throttle body. Even cleaned the oily crud out of them.
-New plugs did nothing
-Fuel rail pressure on my torque app SEEMS to tell me the HPFP is fine. Dealer refuses to diagnose it until I pay them $1100+ For a walnut blast and intake manifold replacement.
-After driving the car around the block with the misfire issue, plugs were black which in my car diagnostic history tells me it's running rich so fuel wouldn't be the issue anyway.

This was a SUDDEN issue. Happened out of nowhere while driving along. Has consistently had the same misfire/rough running/lack of power issue since.

This has got to be a spark issue. But I just can't think of what. The odds that all my coils suddenly went bad at once seems very very very unlikely. What else is there? I would imagine if it was the crank position sensor, it would give me a code specific for that?

 

I'm not a mechanic, but will throw a wild guess out there. Is there anyway to check the timing on these cars? Mis-fire on all four sure sounds like the timing is not advancing at the correct time. Is there a crank position sensor?

 

Don't know for sure, but could it be a problem with the harness going to the coil packs?

 

I am having the same problem here. I have had a loud knock coming from the exhaust manifold for about 5 months and never got the time to fully inspect what was going on.

Have had code p0420 for that amount of time and have replaced both o2 sensors and reset the CEL to clear the code. But would come back on in a day or two.

I just had it at the repair shop and the mechanic there said it was a clogged cat and that it was caused by a misfire. I seafoamed it and thats what I think got all clogged in the cat.

Here is a video shot from my phone of the knocking sound.

 

Sorry double post

 

I believe that is a body code. I got one when I had a misfire its basically a symptom of the misfire, when it happens you get a suddenly loss then regaining of power sending a "shock wave" through the drive train you know that harsh jerking you get through the car when you loss power a then it suddenly comes back-not nice!. I thought I could clear my misfire by flooring it the car backfired and jerked like crazy giving me that code.

 

I had that "shockwave" happen to me on the highway a couple times. Now I know

 

Here are the codes I just got back:

P0693 - Electric Fan Relay 2 Input low

P0420 - Catalyst Efficiency Low (Bank 1)

P1106 - Intake Manifold Sensor Input Low W/Engine Off

P1688 - Electronic Throttle Valve Control 2/3, Air mass Circulation

P0107 - Manifold Absolute Pressure/Barometric Circuit Valve Low

Basically I am not getting a full circulation of air through the car. When driving it home from the shop, every time I would let off the accelerator the rpms dropped to Zero and would stall the vehicle.

The mechanic suggested that I contact a guy in town that works on BMWs and Mercedes to see what he thinks. I will call him tomorrow if I get a chance.

 

Since you sound desperate I'm going to take a stab in the dark

Have you checked your map sensor on the manifold under the airbox could be coated with oil(if so give it a gentle clean with a cue tip), failing or maybe was damaged when you seafoamed the car. If the map sensor is sending the wrong information to the ECU its going to mess up you AFR. You can pick up a new one on eBay for about $70.

This is all just guessing.

 

I had sudden stalling and misfire codes (read with AccessPort) on my 2009 Clubman S around 55,000 miles. Initially it was cylinder 3, then 1, then all cylinders. Stalling occured only on cold starts or after sitting for 30 minutes or more, slowly getting worse over a couple months. CEL would come on when engine stalled/stumbled.

Had my local Mini shop do the intake valve walnut shell blasting for $440. Did not help, but did improve power and throttle response a lot (recommend). Dealership wanted to charge me a lot more to redo the blasting as part of their diagnosis steps, but didn't (they took pity on me and bypassed this step since it was already done). Dealer's diagnosis showed that the HPFP was not the issue (no specific fuel pressure codes, and good pressure I suppose) but they replaced it anyway. This completely fixed the problem!

Bring the car in with the CEL light on and bring photos or evidence of your misfire codes. Tell them my story. Maybe you'll get lucky. HPFP warranty is 10 years or 120,000 miles if I am not mistaken.

These were my codes:
P0304 Cylinder 4 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P2781 Misfire Mult Cyl Max
P2779 Misfire Cyl 4 Max
P277D Misfire Cyl 2 Max
P2783 Misfire Mult Cyl Error
P277B Misfire Cyl 4 Error
P277F Misfire Cyl 2 Error
P2773 Misfire Cyl 1 Error

One more thing... When the car eventually stumbled under hard acceleration and set the CEL, that's when I took it I to the dealership. Prior to that it only stumbled and stalled during cold starts or after sitting. It would set the CEL then too most of the time but it would run fine after 30 seconds or so after the stumbling went away.

 

I have not, I will check it tomorrow and see what happens.

 

When I watch this video I don't hear anything but a very bad exhaust leak.. My guess here would be your exhaust manifold is leaking real bad. If that's leaking real bad that will throw a CEL. If you have a bad manifold leak idk how your mechanic could say its your cat that is plugged! The only way to test a cat on the car is testing the pressure before and after the cat. With a bad manifold leak your test wouldn't be accurate.. good luck!

 

So I took it to a localGerman import shop and the mechanic there said that it was the MAP sensor as well as the exhaust flange I'm letting him take care of those. He also said the thermostat housing needed to be replaced but I told him to hold off on that.

 

Hope you don't get too ripped on the map sensor easy to replace Max 10 minute job. Good luck!

 

He said $300 for every thing.

 

Exhaust flange, maybe he's talking about the gasket between the turbo to the downpipe or between downpipe and cat back exhaust. If so all those parts including map sensor will cost $100 shipped the your door so your paying $200 for labour. If its the gaskets between the turbo and downpipe that will require removing a heatsheild and moving the downpipe, its a pain in the *** so if your not confident to do you self its money well spent especially if it solves your problem. However if its the gasket to the cat back not so difficult, another 10 minute job. Were you smelling any exhaust fumes while driving, if you had a leak you should have.

 

Well I had gotten my tool set stolen over christmas so it really put me back on what all I can take on myself. And yeah I could smell unburnt gas.