Keep the old cat in your possession, might still be good. Lean code on only one bank, spark plug electrodes on that same bank black, makes me think as most likely reason, there’s an exhaust leak allowing outside air to reach that bank’s o2 sensor. Suggest to double check for that.
Contrary to common-sense, outside air will indeed get sucked into the exhaust system as the engine runs if there’s an exhaust leak.
Make sure the oxygen sensors are in the correct location and plugged into the correct connectors, if they are reversed you will get one bank rich and one bank lean.
Just guessing and tossing parts at a problem is generally a losing proposition. Get a firm diagnosis then, buy the parts. Have you tried on a couple of the dedicated BMW forums? Have you tried a shop? (I hesitated to say this for fear of being accused of spamming, trolling and probably other things 1 specific moron can think of.) But that IMHO wasted converter money would have went a good way at a shop to actually find the problem.
Excellent advice. OP’s car has a quite complex engine design, twin-turbo, straight-6, direct injection as I recall. The culprit is probably going to be tough to figure out using typical diy’er tools. Suggest to take car to BMW specialist shop and ask them to provide a diagnosis. They’ll have level-2 scan tools and know how to interpret the O2 signals from each sensor. Once they tell OP what’s wrong OP can fix the problem themselves if they like.
Another diy’er poster here a few months ago had a similarly complex problem, had replaced several components already as a guess , but didn’t solve problem. No progress towards solution here, so he took car to shop. They diagnosed timing belt problem. OP replaced timing belt using a timing belt kit, car running smooth again.
I took the car today to bmw dealership to run tests on it and try to find the problem. They said should replace fuel injectors, coils, and spark plugs. Told me it’ll cost $9000. Told them I’ll think about it
Did you get a written itemized estimate? IMO it should cost far less for the work you described. I’d get a second opinion before having this shop do the work.
Are they saying they are certain (via testing) all three of those parts are faulty on your car? If not, and are thinking that one of the three is the problem but easier to just replace all three and be done w/it, maybe you could start with replacing the one that is the least expensive to replace, presumably that’s the spark plugs. If three spark plugs are easy to replace and three not so easy( i.e. expensive) , sometimes happens with a V6 configuration, replace the three easy ones. Might get lucky.
I’m sort of surprised they weren’t able to tell you exactly which parts are testing faulty.
This reminds me of when I couldn’t reach something on the top shelf of the frozen food section at the supermarket. The staff there had complained on a visit before when I took matters into my own hands for this problem, stood on something I shouldn’t to make the reach. So this time I asked for help. I was thinking they’d bring a step ladder. But no stepladder, instead the staff person stood on the same thing I had stood on … lol … I said “thanks for the help, but I could have done THAT myself!” …
I replaced all injectors, coils and spark plugs. Engine is still misfiring on cylinder 1. I replaced everything myself
Injector on cylinder 1 was replaced before. All others were originals
It’s been a while since last post so I don’t remember all the details (and not going to read again lol)…
Did you do a compression test??? Would have been much easier with the plugs already out…
Sorry you are having this frustrating problem, seems like you’ve been taking a pretty good approach to the problem. Replaced bank 1 cat, O2 sensors, coils, plugs, injectors. No joy. Damn! … lol … hmmm, so what to do?.. I didn’t read the entire thread again, but my sense from skimming through it, is the computer thinks the fuel/air mixture is correct, but it is actually running rich on 1-3 plugs. Are the tips of 1-3 plugs still black compared to 4-6? I can only make a couple of guesses
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bank 1 exhaust manifold has a crack or isn’t sealing to block, gasket damaged. Allows outside O2 to hit O2 sensor, computer reacts by injecting more gas.
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Compression problem on cylinder’s 1-3, with 1 being the worse
I forgot to mention the threads on some of the spark plugs had oil on them. Could it be bad valve cover gasket causing all this misfire problem?
Now all of the spark plug tips were black as well with number 1 and 6 the worst
Sometimes with a hard to diagnose engine problem, it a good idea to start with what you know needs doing. Since you know you need to replace the valve cover gaskets, suggest to start there. Something amiss might be unexpectedly discovered. Is there anything else you are certain needs doing w/the engine? If you haven’t already done it, a cylinder compression test and intake manifold vacuum test seem like a good idea.
BMW N54 Upgraded PCV Valve
VTT-VTTN54UPGRADEDPCVVALVE
Try this especially if your MEF sensor was fill of oil
When a cylinder misfires a bunch of unburned O2 hits the exhaust system O2 sensor. There should be very little O2 b/c the O2 should mostly all combine with the gasoline when the spark occurs. This extra O2 in the exhaust makes the computer think there’s not enough fuel being injected, so it injects more to compensate for what the O2 sensor is telling it, creating a positive fuel trim, black spark plugs tips, and other symptoms consistent w/overly rich operation. Suggest to focus on what is causing the misfire rather than the overly rich running.
Common misfire causes, shop has to go through them one by one
- faulty spark plug
- ignition system producing no or weak spark
- low cylinder compression
- exhaust system restriction
- fuel rail pressure incorrect
- faulty fuel injector
- fuel injector works ok, but isn’t being correctly pulsed by the engine computer