Alrighty ladies and gents, I have a fun little Mini riddle for you: So I have a 08 Mini Cooper S (DOHC Turbo) which is having trouble starting when it has been left to sit for a while. However, once I get it fired up and running for less than a minute, the car runs absolutely flawlessly. If I turn it off it will fire right back up, no problem. But, when it has been sitting for a while (the longer the time, the worse it gets) it will have trouble starting and will display "Random Misfire Sensor" codes. There also seems to be a lot of black smoke coming out the rear when I try and start it after it has been sitting for while.

To me, I would think for some reason it is losing fuel pressure as it is sitting there. However, I mostly work on my Formula Ford and vintage mini, and these computer powered cars are a bit beyond me....

Does anyone have any ideas?

 

Random Misfires? Any specific cylinder misfires also present when you pulled that code? Sounds like its time for Carbon Cleaning service to vehicle (as well as a complete car encoding with new measures to help with Carbon Build Up on backside of intake valves and intake runners, valve overlap re-calibration). If your car runs rough on Cold Start and begins to run better as the vehicle warms up, as well as exhibits random misfire codes, then I'm almost certain that your car is in need of CC service. Possible that you are also seeing misfires in cyl 1 & 4 and possible super knock? Also the black smoke coming out the exhaust when reving it while still cold is a good indication that CC service is needed. I would also add to possibly have your Timing Chain Tensioner measured for deflection to ensure your vehicle isn't misfiring due to a stretched timing chain (08-09 MCS notorious for failures in this dept). Any loud noises coming from engine bay when cold cranking the vehicle for first time/drive of day?

You can have the fault for random misfire pulled @ your MINI dealership and ask for environment data that was present when fault occured. It will contain rail pressure @ time of fault. This will help from a diag stand point if its a possible failing HPFP, or if its just simple CC service, or possibly a failing Timing Chain Tensioner or worse all 3 @ same time (though highly unlikely).

Good Luck, and Let us know what you find out.

 

It does actually give additional codes for cylinders 1 and 4, why would that be? And if it is a carbon cleaning issue, why does it seam to get worse when it has been sitting for a while? (Please forgive the stupid questions)

 

These are common cylinders that seem to always show up when misfires occur due to needed CC Service. It has to do with direct injection as well as the original mapping of valve overlap (or the lack there of). Usually when the dealer performs CC service, they will also perform a complete (if necessary) car encoding of all modules (which will update the current DME encoding) which has improvements to valve overlap to help with carbon build up. CC build up is common for these vehicles due to DI. Bet if you inspected all 4 intake runners you would find an excessive build up in cyl 1 & 4 (probably level 4 or greater) and a descent amount even in cylinder 2 & 3). Either way, I would take your vehicle to an Authorized MINI dealer, and provide them the info you just provided me, and I can almost with certainty say they will inform you that your vehicle will need CC Cleaning as well as a firmware/module update to help.

 

Okay, makes sense. Next silly question: what exactly will they do to the car during the carbon cleaning?

 

they will remove the intake manifold to gain access to the intake runners as well as backsides of intake valves, blast walnut shells down the runners to break up the carbon build up, and more then likely add some lovely techron to your current fuel tank to help with some of the very minor stuff that the walnut shell blasting does not get (but if you get a good tech who does this on the reg, they will know exactly the best method to get 95% of the CC build up out). You will notice an immediate change in your vehicles behavior as well as manor and overall performance. I would also like to add, dont be afraid to run your car hard every now and then. You'd be amazed that doing so will shake the cobwebs out of your valve train as well as get the cylinders nice and hot and help with this issue (reoccurance). I'm not saying go out and run the **** out of your car all day everyday, but every now and then, punch it in 3rd and get the RPM's up there, your car will thank you.

It is also possible that they may measure your timing chain deflection, and based on their findings (weather it be in spec or outside spec) they may replace your Timing Chain Assembly/Kit or just the Tensioner with the updated tensioner (which honestly is just throwing a band aid on a wound that needs stitching). It will all depend on what the Tech decides as well as how he goes about diag the vehicle and what BMWNA/PUMA state the technician can or can not do (that is if it is warranty based work). How many miles on your vehicle? Extended Warranty?

 

Hahahaha, cheers mate. I am sure it will amazingly BMW expensive, but it sounds like it needs to be done. The part I don't understand is how it happens when the car has been sitting, but has no problem starting up when its been running a while? How can carbon build up do that?

 

Also, its a 85K mile car that had a engine replacement at 45k. No warranty.

 

Well carbon build up occurs due to the n14 being DI. With that stated DI vehicles directly spray fuel which has detergents in them to help keep the insides of your vehicle clean into the cylinder, where as port injection will spray atomized fuel on the backside of the intake valve which in turn helps keep the intake runners and backsides of the intake valves clean as they are being exposed to the detergents that were intended to clean. This muddled with the poor PCV system design and you have the issue you are experiencing (combo of no real cleaning of backside of intake valves, accumulation of oil and carbon build up, create this nice tar like substance that choke your engine in the combustion process). Once your engine starts to warm up or better @ operating temp it does begin to remove some of the carbon deposits due to cylinder temps burning off some of the carbon deposits. Only problem is, once you shut your engine off, the bit of fuel that would be left on the backside of the intake valves on a port injection vehicle is not present on a DI engine, and your in the debacle your currently in.

This is why the Lexus ISF does not exhibit these issues as it is both DI and PI.

As for the total mileage on your vehicle, sounds about right in terms of total mileage on new engine (roughly 40k on replacement engine). With it being a new engine though, I'm almost certain that BMWNA/PUMA Engineers are going to want to have a visual inspection of your timing chain, upper timing chain guide as well as timing chain tensioner deflection to ensure your new engine doesn't have a timing related issue due to a stretched timing chain. This may lengthen the process as well as down time of the vehicle. Though since its not in warranty they may not have to jump through these hoops and may just go to offering you the CC Cleaning service as a first solution to your current issue.

Good Luck, and let us know the outcome when you find out.

 

Sounds like a high pressure fuel pump or carbon build-up issue based on what a lot of other people have experienced. Carbon build-up is easy to see visually, but you need a BMW diagnostic tool to be able to see how the high pressure fuel pump is cooperating with respect to how the ECU is commanding it. Without the diagnostic tool you are just guessing whether or not the high pressure fuel pump is working correctly.

 

How could I visually check to see if there is carbon build up?

 

Remove the intake manifold and take a look at the intake ports and valves. If you can't see the smooth metal finish on the valves they need to be cleaned manually. I cleaned mine manually last year with carb cleaner and some gun cleaning brushes. If you see carbon buildup here, you'll likely have it in the combustion chamber too. The only way to try and reasonably tackle that is with some fuel system cleaner like Redline SL-1 and an Italian tune-up

 

Like stated by above poster, you can remove the intake manifold, which is not a difficult task (5 13mm nuts that hold the manifold on studs to cylinder head, there is a 10mm 1/4 inch length bolt that is used to attach the I-manifold to a bracket. You don't actually have to take the manifold out entirely, just rock it back off the cylinder head far enough that you can get some light down the intake runners and use a inspection mirror (recommend a small mirror) to visually view the build up. You will more then likely see this nice "tar like" substance that has accumulated around the backside of the valve and has covered the valve stem working its way up into the valve guide (one of the major flaws in the n14 cylinder head design...) as well as if you were able to see it slightly gathered on the seat which is causing the valve to not seat correctly as well as does not allow the intake runner to flow air properly into the chamber for proper combustion which is some of the reason(s) for your misfires.

Honestly if you want it done correctly, and cleanly I would recommend you just having an Authorized MINI Dealership, or a reputable MINI Shop perform this. Simply using carb cleaner and some fuel additive cleaner of your choice (I actually like Redline SL-1, it works ****!) will not do the job that a proper walnut blasting/Vac Job will do (i've seen the hack job attempts that some have done, and while they worked to an extent, eventually it all came back because their vehicle did not receive the dme module programming/update which is key in helping somewhat in preventing Carbon Build up from (re)occurring so quickly). Unfortunately though, like stated earlier, its a semi-downfall of DI, especially in the MINI.

Good Luck!