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Thread: Confuse by Misfire, but Happy!!

  1. #1
    Join Date
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    2002 M3, 2008 Z4M Coupe

    Confused by Misfire, but Happy!!

    First post for a new user.

    Here is (was) the problem. 2002 M3 SMG, sitting at traffic light, car not warmed up, and engine starts misfiring, CE light goes on. Restart the car 4 times, no change. Limp, and I mean limp, the car home, barely would run. Did not like accelerating at all. Car has been in family hands entire life, always garage kept. 137k miles on clock, always maintained very well.

    Read codes, misfire #5, misfire #2, multiple misfire, camshaft position sensor - exhaust, cat convert inefficiency, and one other code for camshaft-crankshaft sensor out of phase, or something like that. Start my month long diagnosis, remove cabin filter housing, remove spark plug/coil cover. First off, replace CPS, and clear codes. Start car, after listening to misfire for a minute or so, CE light goes on. Misfire 2, misfire 5, multiple misfire, but no CPS code. 1 issue hopefully fixed. Next swap coil packs around, clear codes, restart. Still misfiring, CE light goes on. Misfire 2, misfire 5, multiple misfire. Next, swap spark plugs around, clear codes, start engine. Same result, CE light goes on, misfire 2,5, multiple misfire. Next step, and a big one, swap fuel injectors around, and once again, no change. All comes back to Cyl 2 and Cyl 5. Cylinder 2 misfire has always been less frequent that cyl 5 misfire, but it did show up at times. At this point, I believe I have ruled out spark plug, coil pack, or fuel injector issue. Visibly, all of those items looked good. Lets do a DME reset, IE leave battery ground disconnected overnight. Next day restart, no change. Worry now sets in. Valves haven't been done since 60k, so lets do a compression check. Worry, worry, worry.

    Compression check shows all good, whew. 167-174 psi in all cylinders. 167 on cylinder 1. Starting to think wiring or DME issue, but for kicks and it can't hurt, order up some new plugs and coil packs, wait a week. Meanwhile, remove DME and cover, look for any obvious sign of issue (smoke let go from chip, burnt component, burnt traces). Nothing. Now thinking wiring, or internal issue with DME. All connectors and terminals look good with no corrosion. Painfully check fuel injector and coil pack wiring with an continuity meter end to end, that is, from the component connector, back to the DME connector. Tedious indeed, but all wiring checked out good. Now i am really thinking DME issue. There are DME tester/rebuilders out there that aren't too expensive, but replacement is.

    Before driving down that road, lets look at throttle body linkage, long shot i know, but worth the relatively easy check. Remove intake plenum (not TB housing), and check that all TB flaps are moving. Funny thing, can't operate the fly-by-wire TB's without putting car in neutral (its an SMG car, save the comments). Reconnect the SMG controller, which is located next to the DME in the engine bay, put car in neutral, still no throttle body movement. Reconnect the DME, TB movement! All TB's moving as they should, no issue there. Really looking like DME issue now, right?

    Since everything is connected, lets give her a start. Refresher - new CPS, new plugs, new coil packs, fuel injectors checked, throttle bodies checked, wiring checked.....all good. Clear all codes, start car. NO MISFIRE!!! Let car warm up in gargage, NO MISFIRE, no CE, no codes. Go to bed on good note.

    Next day, drive car for 25 miles or so, NO MISFIRE, NO CE, NO CODES. Car is running like it should. So what gives? I need someone who knows the S54, and the Siemens Control System to explain.

    Please help me understand. Has anyone else had this experience?

    Possible causes:
    Resetting of all connectors cleaned, or reestablished good electrical connection.
    Siemens controller reset itself, which had previously shut down cylinder 5 fuel due to misfire and to protect cats. I read this on one of the forums that it can do that.
    New components combined solved the issue.
    Phase of the moon increased gravitational pull on my M3, solving all gremlins......

    Sorry for the length here, appreciate anyone that took the time to read, and respond of course.
    Last edited by KBBM&M; 06-25-2022 at 01:28 PM.

  2. #2
    dworthy's Avatar
    dworthy is offline Wagon meister :) BMW Tech Expert
    Join Date
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    16 220i 05 325it 05 M3
    So you cannot reset a modern BMW by pulling the battery anymore, basically any OBD-II car.

    As you like BMW's, and older ones at that, I would invest in a D-CAN cable and put INPA or ISTA on to a laptop so you can get the factory fault codes and not some generic government mandated ones.

    This will allow you to reset the adaptations, watch live data and really see what is going on. While I do like hand scanners for quick checks, for real diagnostic work, I only use INPA or ISTA which I have both and will depend on what car I am working on.

    As far as the issue just going away, you could have had a bad connector and all the fiddling around allowed it to fully seat, but in the firing order of 1, 5, 3, 6, 2, 4 you would have 2 cylinders firing then dropping 1 which can be very rough to drive. Once a misfire is detected, the DME will shut of fuel to keep it from washing the cylinder walls with fuel and putting raw fuel into the exhaust thus damaging the Cat's.

    Lastly I hope you cleared codes every time you moved a plug or coil around, otherwise the DME won't start fueling those cylinders.
    Darin
    Current:
    16 220i Active Tourer Platinsilver MET (C08)/Dakota Black (PDSW), P7ACA, P7LDA, P7LHA, P9BDA, 6sp Manual - Wife's new toy!
    05 325it Electric Red(438)/Gray(N6TT) ZCW, ZSP 5sp Manual Back set cover, trunk mat, Euro Infra-Rot front windshield, and mud flaps! Mr. Wagon My new Winter car.
    05 M3 Imolarot II(405)/Gray(N5TT) ZCW, ZPP 6sp Manual C.F. Lip, CSL diffuser, SSK, Euro Infra-Rot front windshield and a trunk liner! Mr. Go_Fast Stored for the Winter
    Past:
    95 318is Montreal Blue Met (297)/Beige(K1SN) RIP, killed by an Idiot.
    84 M535i gray market Burgandy Rot Met/Black Leather Lowered by Intrax on bilies, poly everywhere, B&B cat back system, K&N, and a hitch! Da Beast - Still running w/400k+!
    91 316i euro Tizianrot/Gray cloth - E-36 w/M-40 RIP, but great on gas! Best was 38 MPG
    82 528i euro Saphire Blue Met/Blue Leather RIP
    79 525 euro Green/Green RIP
    79 318 Silver/Black - The first one that got it all started
    M-Flight Member

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