I have a 2003 BMW 318i and had issue saying misfire on cylinder 4 only. Replaced spark plugs, coil packs, injectors tested and also compression tests done on cyclinders 1 and 4 and all came back fine. Swapped coil packs as well and issue stays on cylinder 4. Been told it could be caused by timing chain issue possibly being stretched. Is this likely to be causing only an issue with 1 cylinder rather than all of them. Any help appreciated. Thanks

  • What is the actual on board diagnostic (OBD) code? I’m curious to know how this “misfire” issue is detected. E.g. is this a signal coming from the knock sensor? Timing chain length issue? I’m not so sure. Possible as that sets up cam timing hall effect sensor as well as valve timing. But personally I’m thinking heavy carbon deposits in one cylinder causing pre-ignition knock. Have you looked inside of each cylinder with endoscope?
    – zipzit
    Jun 9 '21 at 18:34
  • @zipzit - Knock/pre-ignition is going to register different in the computer from a misfire. A misfire means there's no ignition happening in the cylinder (at some point and time). Jun 10 '21 at 0:16
  • Welcome to Motor Vehicle Maintenance & Repair! I'm going to assume you've cleared the codes? Jun 10 '21 at 0:17
  • @Paulster2 Er, not. 2003 model year, not many vehicles could ever determine if spark was actually occurring. Think about the sensors in use in that period. Hall effect, delta voltage, pressure transducers. Spark? not so much. You can read the input control signals easily for spark, but high voltage output from ignition module, no go (in 2003) I really want to know the original OBD code displayed here. In general terms OBD circa 2003 feedback is great for fuel related issues, not so valuable for spark or airflow (plugged filter) issues. But I'm talking generic terms, not BMW specific..
    – zipzit
    Jun 10 '21 at 14:31
  • Is this question a duplicate?
    – zipzit
    Jun 10 '21 at 14:34

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