5-Series (E12,E28, E34, E39, E60)Chat relating to the BMW 5-Series of all generations. Specific models include: BMW 518, BMW 520, BMW 520i, BMW 530i, BMW 528i, BMW 530i, BMW 518i, BMW 524d, BMW 525i, BMW 525e, BMW 528e, BMW 540i, BMW 535i, BMW 520d, BMW 525td, BMW 525d, BMW 530d, BMW 525i/xi, BMW 530i/xi. (BMW 5-Series Forum)
I need some help with this. I have been chasing a Misfire that's driving me insane on my 60,000 Km 523i E39 for 18 months now.
The problem starts as as intermitent misfire but the OBCDII won't register anything. Then it progressively (days and weeks) gets worst until it gets so bad that it goes into "cylinder cutout". When that happens the OBCDII will register a misfire failure on Cylinder 5.
My mechanic has changed the O2 Sensor, All Coils, All Plugs, had my injectors professionaly cleaned. All this helped for a couple of days, but now I am starting to get a little misfire again, and the computer doesn't register anything yet. What else can it be? What can cause a misfire besides all of what I have changed and why wouldn't it be caught by the computer until it cuts off the cylinder.
Thanks for any help pointing me in the right direction.
First of all cleaning the injectors is not a guaranteed fix for a faulty injector.
I recommend swapping the injector on cyl #5 with another cylinder (cyl 2 would be a good 1) and see if the fault follows the move, meaning clear the fault, drive it and when the fault reoccurs see if it is now storing a misfire code for cyl #2. If so then you know the injector is faulty.
Other causes besides what your mechanic has checked or replaced would be of course internal engine problems, most commonly being a sticking lifter on cyl#5 or even possibly a valve failure like a burnt valve or even piston or cylinder wall damage. Has the mechanic performed a leakdown and compression test? If not then he should.
Another possible cause would be a vacuum leak on the cyl#5 intake runner. Lastly but not as likely with the misfire fault being in only 1 cylinder would be a vacuum leak from something like the cyclone separator or even possibly a damaged/plugged catalyst.
Also you asked why does the the system not set a fault when the engine misfires until cylinder cutout is present and the answer is it DOES set a fault. It may not however turn the check engine lamp on until the control module has seen the fault for a long enough period of time to initialize cylinder cutout. Anytime there is a fault stored for "misfire with cylinder cutout" stored there is always an additional fault which was stored 1st for "misfire Cyl # __) it may be that your mechanic does not have a code scanner sophisticated enough to pick up these sort of faults, but I assure you that they are there.
My mechanic uses the same software and reader as in the dealer, but you were right on the storing of the messages before cutting off the cylinder. Eventhough It hasn't cutout the cylinder I took it to the shop yesterday and there were two messages on the memory. Once again the misfire on Cylinder 5 and a coolant return temp sensor out of range or something like that.
The strange thing on the error messages is that we cleared the memory, drove it the whole day with the ocassional misfire, then we checked again today and No messages. So, it seems like it depends on the severity of the misfire in order to First register it on memory and after it gets really bad initiate cylinder cutout.
My car is in again for more testing, and I will sugest to my mechanic the tests you mentioned. He doesn't think is an internal engine problem, since the engine looks fairly new, low mileage and has never overheated...
One last question, can it be fuel delivery related? When all this started (18 months ago) was about the same time my fuel pump died and got replaced. But it does not sound to me related, does it?
I really do not think fuel delivery would cause this issue. IF the fuel pressure was low or erratic you would have misfires in multiple cylinders, not just 1. As I mentioned in my last post if I had to guess I would say you have either a faulty injector or a sticking lifter on cyl # 5. This is assuming that your mechanic as you mentioned has replaced the spark plugs and the coils with True BMW factory parts. Also makes sure that he used Bosch coils and not BREMI, the BREMIS are known for problems. Beyond that and all of the things that I mentioned in my last post, 1 more possible cause could be a faulty Engine module (DME) or the wiring going from it to the injector or the supply to the ignition coil.
Im sure your mechanic knows all of this as well. Best of luck to him and you in getting this straightened out.
For sanity's sake, we decided to clear the memory, test the car for a few more days and see if the error codes were the same. I drove the car for a couple more days where the misfire was making a mess out of driving, came back and guess... No error codes! This got us very suspicious...
I also noted that when I turn on the key, all the service lights initially light, EXCEPT the Service Engine light... which never shows…
We recreated the problem in the shop, Powerbraking the car, putting it in Drive and accelerating between 1.500 and 2.000 RPM. You could feel constant misfire, and we could recreate it at will... Then after an hour or so, with the scanner connected, an ignition fault to cylinder 3 was detected and it shut it down. Hmm, now a different cylinder. Also, we noted the misfire was worst at this RPM under electrical load (e.g. A/C on, lights on).
We cleared the memory with the car running instead than just with the switch on, and like magic the misfire went away, and we haven't been able to reproduce it since yesterday...
I personally now believe we could be facing a faulty ECM or a faulty ECM main relay at best. I assume that would explain why the Service light doesn’t turn on, why the error codes are not always present, and the crazy misfires under load and low RPM. At least it sounds like it is electrical – related…
My mechanic is now trying to get me an ECM and relay from other E39 so we can test it once the problem appears again...
Couldn't help but reply with more questions.
My 1997 523i has just started this week to misfire under first acceleration through 2nd, 3rd and 4th gears at between 1200 and 2000 rpm. IE: taking off gently without redlining it ... is this similiar to your problems and what might be the general outcome. I have to say that my 523 smokes for a few seconds on start up from cold overnight and has the first plug a bit sutty. Valve stem seals I suspect. I've recently replaced the crankshaft sensor which cured a really low power problem when I first bought the car. Oohh, 114k on the clock. Worth noting, the rocker cover has been off my engine before .. gasket maker visible on edges ..
Thanks for any info ... having been a Nissan 200 guy before this, taking out an engine isn't new but preferably avoidable ....
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