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Thread: Misfire driving me spare

  1. #1
    Join Date
    Jul 2014
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    Adelaide
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    41

    Misfire driving me spare

    Help folks.

    Still the same car here- 2005 V6 petrol D3.
    Some time last year I replaced the engine for a major timing chain mishap and it was cheaper to replace than repair. Sourced a lowish km motor from a forum member in NSW.

    Now I have a new misfire problem. At idle and with throttle. From cold and hot. It is driveable and intermittent misfiring but I don't like to tempt fate here and not pushing it. Under load it is much more prominrnt

    OBD code only for cylinder 5 misfire and occasionally 'misfire in first 1000 revolutions'.

    I have changed all plugs and leads, cleaned and checked connections, swapped coils around, and even spent good money on injector cleaning and testing (all 6).
    Still the misfire persists.

    I am operating on an assumption which I just realised, that the 5th cylinder is at driver side firewall. Can someone confirm this is the correct cylinder?

    Alternator is a bit noisy and putting out 30V AC at idle but de-energising this before starting changes nothing and the misfire persists.

    I am lost here. I am thinking one of:
    - a higher level electrical issue, such as the AC ripple damaging the ECU/PCM
    - spark issue with wiring
    - incorrect cylinder getting my attention as I have not changed all the coils- need confirmation re layout of cylinders as above
    - sticking valve (based on the intermittent misfire) but you'd think this would change as it warmed up
    - another mechanical issue, but it runs very quiet

    Any help here would be very gratefully received. I have made this a really nice car and it has been treated nicely in my hands and this is making me crazy.

    Julian

  2. #2
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    What about crank angle sensor and or cam sensor if fitted ?
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  3. #3
    Join Date
    Jul 2014
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    Would that throw just a single cylinder off?
    Is it a matter of changing for spares and seeing?

  4. #4
    Join Date
    Aug 2006
    Location
    Kingston, Tassie, OZ.
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    Alternator needs to be changed out first if noisy, can't believe that wasn't the first thing done, may have saved some money and time...
    These crank and cam sensors are VERY sensitive to electrical noise, not saying it's a 100% fix in this case but electrical noises are first port of call.
    The Isuzu 110. Solid and as dependable as a rock, coming soon with auto box😊
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  5. #5
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    Isolating the alternator (as in functionally removing it) lead to exactly the same misfire so it seems as a cause it is not likely. A new alternator is $6-700 for a Denso unit .

  6. #6
    Join Date
    Jun 2013
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    Aberglasslyn NSW Australia
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    193
    Quote Originally Posted by Julian B View Post
    Isolating the alternator (as in functionally removing it) lead to exactly the same misfire so it seems as a cause it is not likely. A new alternator is $6-700 for a Denso unit .
    Functional removal? Belt off? Reg unplugged, battery cable unplugged? My alternator was noisy, but not for long before it died. It's always cheaper and easier to completely rule out known problems when diagnosing. they won't always cause the issue to resolve but they will stop other problems during the search.
    Mechanical faults such as a valve are unlikely for a misfire. Can be easily and cheaply tested with a compression test.
    Test the ohms of each injector. You can also check the ohms of the coil but I think it'll only show the primary winding from memory.
    With it running go through and shake the wiring "tug test" lightly pull the wires .
    Have you confirmed that it is number five? Disconnect either the plug or injector on that cylinder, if the engine doesn't change note. Then it's the culprit. If does then move on to the next cylinder. When you get to the cylinder that doesn't respond to the injector or plug being disconnected. Swap one component at a time till the cylinder next to it becomes the problem. If nothing makes the cylinder number change. You need to test wiring using a multimeter and diagram for continuity. Unlikely though. Will usually through an open circuit code.
    Coil over plug type coils don't live forever.
    If at first you do not succeed, maybe your just no good and should quit!

  7. #7
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    Just replace the alternator, regardless....🙄
    The Isuzu 110. Solid and as dependable as a rock, coming soon with auto box😊
    The Range Rover L322 4.4.TTDV8 ....probably won't bother with the remap..😈

  8. #8
    Join Date
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    Adelaide
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    Quote Originally Posted by justinc View Post
    Just replace the alternator, regardless....🙄
    I intend on doing so. I need to defer the cost for a week at this point.


    Quote Originally Posted by josh.huber View Post
    Functional removal? Belt off? Reg unplugged, battery cable unplugged? My alternator was noisy, but not for long before it died. It's always cheaper and easier to completely rule out known problems when diagnosing. they won't always cause the issue to resolve but they will stop other problems during the search.
    Mechanical faults such as a valve are unlikely for a misfire. Can be easily and cheaply tested with a compression test.
    Test the ohms of each injector. You can also check the ohms of the coil but I think it'll only show the primary winding from memory.
    With it running go through and shake the wiring "tug test" lightly pull the wires .
    Have you confirmed that it is number five? Disconnect either the plug or injector on that cylinder, if the engine doesn't change note. Then it's the culprit. If does then move on to the next cylinder. When you get to the cylinder that doesn't respond to the injector or plug being disconnected. Swap one component at a time till the cylinder next to it becomes the problem. If nothing makes the cylinder number change. You need to test wiring using a multimeter and diagram for continuity. Unlikely though. Will usually through an open circuit code.
    Coil over plug type coils don't live forever.
    Josh, yes I pulled the regulator cable so windings couldn't energise, and got a suitably grumpy chime and warning re no charging state and the AC voltage disappeared.

    I agree that it seems unlikely mechanical.

    Injectors were a completely different set professionally cleaned and flow tested accurately, all very close resistance. Fault remained following change. Manifold gaskets renewed with genuine at the time.

    Coils each have 4 wires so not sure what values across what pins I am searching for. Also I swapped around coils and fault persisted.

    Your check re isolating misfire by pulling components from cylinders sequentially is a familiar routine before I had vehicles with computers. Can I not trust the computer to tell me it is this cylinder?

    Given that the misfire is not continuous, pulling spark to locate which one may not yield certain results as this is subtle at idle and making one cylinder dead will make it buck like a horse irrespective of the cylinder.

    Any ideas about cause from someone who can read my process so far and advise next step. I am aware that the alternator is in need of replacement, as I listed the AC ripple voltage for this reason, but when this stray AC voltage is removed the problem is unchanged. Any further ideas from an electronics expert on these motors?

  9. #9
    Join Date
    Apr 2015
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    What type of scan tool are you using?

    If it is a decent one you should be able to access the generic OBDII modes. You'll find misfire data in Mode$06. Have the unit plugged in and monitor it while you drive. Also check your long and short fuel trims and 02 sensor performance.

    It could just be a vacuum leak. I've seen quite a few misfires caused by a dodgy hose or PCV.
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  10. #10
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    I'm not family with these engines, you mentioned leads earlier ? An Auto electrician with an oscilloscope should be able to look at the current in each one and tell you about spark condition. I've done it to a Falcon a long long time ago. Pull number 5 plug again and look at it. Compare to another. Component change on cars with computers is the same as before. Move the part. Move the problem. Yes you generally can rely on them to be right with which cylinder. But. There is always external variables that add to the misery
    If at first you do not succeed, maybe your just no good and should quit!

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