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  #1  
Old 02-29-2020, 01:58 PM
Looking-2-win Looking-2-win is offline
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Misfire monitor question?

My 2003 Z4 3.0 started to run rough & the Check Engine light came on. Code reader said #5 cylinder misfire detected. OK, I replaced both the spark plug & coil. Cleared the error code and started it up. Purred like a kitten (and the light was off).
Drove about 5-6 miles and the same thing. I still had the code reader with me so I pulled over & checked it. Same error detected. Knowing it wasn't the plug or coil I re-cleared the error and restarted the car...purred again. I did the test drive and it happened again & again but at different mileage times.
Any suggestion as to what might be causing these false alarms? Is there some misfire monitor part that might need replacing (but only blames cylinder 5) ?
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  #2  
Old 02-29-2020, 09:17 PM
Andyz4 Andyz4 is offline
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When you say "it happened again and again" do you mean it misfired or just the CEL lit again? Because at first you said it ran rough with CEL and later you called it a false alarm.
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Old 02-29-2020, 09:47 PM
Looking-2-win Looking-2-win is offline
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Sorry for the confusion... I drive for a while and then the engine starts to run rough and the check engine light comes on. I pull over, turn off the engine, connect the code reader & it says the 5th cylinder misfire has been detected. I clear it, start the car & all is great... for a while driving then it happens again. I spent a few hours driving around and it kept happening a few times always running great after I clear the error code.
It wouldn't run great if the spark plug or coil was the problem so it must be something else triggering the error monitor part. I guess... ??
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Old 03-01-2020, 06:20 AM
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GeorgeT GeorgeT is offline
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Fouled injector maybe?
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Old 03-01-2020, 09:47 AM
pokeybritches pokeybritches is offline
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Is it still running rough before the CEL illuminates? Is it always cylinder 5? What modifications have you done to the car? At what rpm and load is the misfire occurring? What did the old plug look like?

If its always cylinder 5, Id next look at a possible injector or wiring issue. If the misfire has changed cylinders, it could be the MAF sensor, an oxygen sensor, catalytic converter failure, intake or exhaust system leak, or something in the fuel system like a clogged filter or failing fuel pump.

Rough running is detected through the knock sensors IIRC.


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Old 03-01-2020, 10:52 AM
Looking-2-win Looking-2-win is offline
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The check engine light comes on as soon as it starts to run rough.
It is always cylinder 5.
Always runs great as soon as I clear the error code.
Runs great for different lengths of time between the code errors.
The old plug looked fine. (no oil-foul)
No recent modifications or changes done. (Last thing was a regular oil/filter change)
Have had no issues for a long time until this. (been lucky)
The electrical connector on the coil looks to be fine. (no damaged wire or connector)

Have never messed with injectors... how do I test to see if that's the problem?
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Old 03-01-2020, 06:34 PM
Andyz4 Andyz4 is offline
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If the engine runs smoothly for some time after you clear the code, logic says if a plug, coil or injector was bad the misfire would continue. It's really odd that clearing the code makes it run better, if temporarily. Makes me think the computer is putting the car into "limp home" mode until you clear the code.
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Old 03-02-2020, 12:17 PM
Looking-2-win Looking-2-win is offline
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Thanks for confirming my opinion that any mechanical part failure wouldn't be fixed by clearing the code. The more 'computer-issue' it is the less in my repair comfort zone.
Is there some diagnostic tests I can do to narrow down the problem area?
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Old 03-02-2020, 07:51 PM
darkslyde darkslyde is offline
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Without a proper BMW scan tool (OBD-II scanner that translates BMW specific codes) it's hard to really isolate the problem.

Things I can suggest:
Check that spark plug, if it has excess fuel, then your injector might be busted and pushing too much fuel. To test if its not pushing fuel out, you'll need to remove the injectors, and have it push fuel out, if one of the nozzles's not spraying, it might be just clogged and some additives/injector cleaner might fix it.
If you hear ticks, your valve lifter could be the issue. Try using some additives (i.e. liqui moly hydraulic lifter additive) to see if that will work, if not, that's a lot of work just to get to the lifter. (Bad oil/bad maint habits will cause carbon buildup overtime).
If you have a BMW scan tool and can control the DISA valve, you can manually turn it on or off, you'll know if that's the culprit. (Must be done under care).
Check under the intake manifold, if the vacuum hose is toast, then the leak can lead to misfires. Could be a breather hose issue too. (I think you get an evap code with that too).

Hope you can figure it out.
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Old 03-03-2020, 08:14 AM
Looking-2-win Looking-2-win is offline
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Thank you very much for the suggestions .
The first step will be getting to a proper BMW scanner. I can look for a possible vacuum tube leak in the mean time.
Thanks again !!
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Old 03-04-2020, 01:40 PM
Lyarasheski Lyarasheski is offline
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Double check the spark plug as others have said. If it's good then it may be a case of the knock sensor giving you the wrong cylinder number. I've had it happen a couple of times because they are closest to #2 and #5
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Old 03-04-2020, 03:16 PM
Gregory_tolson Gregory_tolson is offline
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Did you check to see if there is oil pooled up in the spark plug tube? Possible valve cover leak?
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Old 03-04-2020, 06:31 PM
darkslyde darkslyde is offline
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Quote:
Originally Posted by Looking-2-win View Post
Thank you very much for the suggestions .
The first step will be getting to a proper BMW scanner. I can look for a possible vacuum tube leak in the mean time.
Thanks again !!
Just borrow one if you can, cause those diagnostic tools can get quite expensive.
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Old 03-05-2020, 04:53 PM
Looking-2-win Looking-2-win is offline
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OK... Today was a perfect 70 degree cloudless ( top-down) day so,
I was driving all day long and not a single 'misfire-check engine light' problem (for hours of city & hwy driving) Until...
I stopped for dinner then headed home... a few miles from home it happened again.
I turned into an auto parts store for them to use their code reader. They looked up the code they got on their computer specifically for my car. Same thing, cylinder 5 misfire detected. They could only suggest having a BMW mechanic search for some electrical problem.
I cleared the error code and as usual it ran great back home. Very frustrating!
Not sure what "limp home" mode is but there has to be something that is tricking the ecm to think it's a #5 misfire to convert the system into that limp home thing.
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Old 03-05-2020, 04:59 PM
Looking-2-win Looking-2-win is offline
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And as far as the oil fouled plug suggestion, no the old plug was (& is) good. The new one would have fixed it if it was the problem. The spark plug 'well' was dry and clean.
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  #16  
Old 03-05-2020, 09:00 PM
Lyarasheski Lyarasheski is offline
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Move coils #4 and #6 to #1 and #2. It sounds like it is just flagging the wrong cylinder if you only did the one coil
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  #17  
Old 03-05-2020, 09:02 PM
Andyz4 Andyz4 is offline
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Suggest removing electrical connectors to both the coil and injector on #5 and give them a good shot of contact cleaner before reinstalling. If that doesn't fix it, try swapping #5 coil with another cylinder and see if problem moves to that cylinder. If not, try same trick with injectors..that should narrow it down.
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