Car is dieseling

Discussion in 'Technical' started by AAU54U, Mar 4, 2013.

  1. AAU54U

    AAU54U Member

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    My car is going well, great power etc but this last week it has decided to start dieseling.

    http://youtu.be/hq3_CUTK3Rc

    I dont know if this is related to the fact I accidently put 91 octane (with 10% ethanol) in the car last week. When I realised my mistake I drove home gently then got a mate to come over and syphon the petrol out into his car, fortunately his commodore was nearly empty and could take all the fuel (couldnt syphon from the fuel cap for some reason but had to go in via the cover on the tank).

    There was about an eighth of a tank left when we finished syphoning (I needed to leave some in to get back to the station). I filled up again with my usual 98 octane Shell V max. I also put in two bottles of Nulon Total fuel system cleaner because that has been proven to raise octane significantly.
    I'm also trying to avoid going into boost until I've burnt up the current tank and refilled again to further dilute.

    The idle is high because it needs to be (car will stall when dropping from high rpm otherwise - UAS have done the best job they can to fix but there is a problem with my computer or something - at least it doesn't flood on start up anymore). AFR is around 11.5, recently had Nistune tuned at UAS (Boost is 15 psi).
     
  2. East Coast Z

    East Coast Z Well-Known Member

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    So, if you change the ECU your problem should disappear?
     
  3. AAU54U

    AAU54U Member

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    Presumably. I've even got a spare TT ECU. Just a hassle swaping Nitune over to the new ECU. I wouldn't do it myself either I'd get UAS to do it, and that costs money (of which I have spent a ton on the car in the last year - and just recently to get my idle fixed and Nistune tuned - so not in hurry to spend more just right now). I can live with the high idle anyway. I can live with the dieseling too (probaly disspear when my fuel is fully back to normal 100% VPower)
     
  4. East Coast Z

    East Coast Z Well-Known Member

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    No, just swap the ECU over to see what happens.
    The idea of Nistune is to be able to adjust the ECU to suit your engine.
     
  5. AAU54U

    AAU54U Member

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    Well I guess that would be the quick way to tell if it is the ECU or not.
    But if it does turn out to be the ECU I've still got to transfer the Nistune board into the correctly working ECU (if I want my idle fixed and a properly tuned ECU).

    Which rasing the question of: if you swap Nistune into a new ECU but the same engine does it need to be retuned?
     
  6. East Coast Z

    East Coast Z Well-Known Member

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    How good a tune do you think you got, if the tuner suspected the ECU of being faulty?
     
  7. AAU54U

    AAU54U Member

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    The butt dyno (which is what really matters to me) says power is good. I am really, really happy with how it drives and accelerates. Couldn't be happier.

    At present the cars limitation is how much acceleration its driver can handle not how much the car can deliver (which is the way it should be so I am quite happy).

    Below are the results from the tune.

    [​IMG]

    [​IMG]
     
  8. Sanouske

    Sanouske Retired Moderator

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    That is very freaking odd. Silly question I have for you, but you don't have a turbo timer wired into your zed do you?

    I'd never come across an efi engine that wil "diesel" on after key ignition cut off. Just doesnt make sense. Something's having to have been tampered with for this to happen.

    Was it doing this prior to nistune editing?

    I would put in the other ecu and test what's happening. Regardless of your tune and idle adjustments etc, would be keen to see if when power is cut. That the ecu isn't still functioning to keep the engine running.

    To be honest, I wouldn't be surprised if the only reason why its stopping is that the fuel pump has stopped supplying fuel and the engines running on from residual line pressure. Does it take a bit to prime in the morning. Or next start up phase.

    I'm surprised uas didn't look into this further...
     
  9. grub

    grub New Member

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    just a thought have you checked the ignition relay
     
  10. Wasgood

    Wasgood New Member

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    Two bottles is too many.
     
  11. Kieren

    Kieren Active Member

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    Mine did this before I purchased it. The compliance guys had managed to fry every computer on the car when they were welding in the intrusion bars and as a result the car would still run with the key off and removed.

    The importer ended up replacing at least the ECU, ATCU and FPCU.

    I guess I'm saying it could be the FPCU and/or ECU that's faulty and causing the problem as they would have been the cause in my case.
     
  12. AAU54U

    AAU54U Member

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    It wasn't doing this when UAS had the car. Its only started last week after my funny fuel mix of 91 octane + 98 octane plus lots of fuel cleaner. I'm optimisitc it will resolve itself once the current tank is empty and I refill with the proper fuel.

    Yeah it is behaving like it has a turbo timer in it, except it doesn't.

    Yes it is odd that it can idle that long and that smoothly presumably without a spark. I've had dieseling before whe I had a 260Z but it was nothing like that smooth or long running.

    The start in the morning is instantaneous. Either hot or cold that start is instant.

    I have had trouble starting in the past but. Before taking it to UAS while it would start instantly when cold, if I tried to restrart within say 2 hrs of stopping the motor would only go up to about 300 rpm then die, unless I gave the throttle a quick blip then it wouldnt die and all would be well. But if you didnt catch it on the hot start and let it die then on the next restart the motor would be flooded and I would have to remove the fuel pump fuse and burn off the fuel then it would start OK (that didnt happen too often). I had the Idle control valve (whatever you call it) replaced but it didnt solve hte problem. On my last trip to UAS they found a lot of wiring problems they fixed including a wire with a melted sheeth.

    When I got the car back from UAS I found the boost gauge wasn't working and the battery charge light was coming on faintly. I found an engine ignition fuse or something was burned and so replaced and the the gauge was then working and battery light went away.

    It only diesels if the motor has been running a while before you turn it off. Dieseled for about 30 sec when I got to work this morngin but when I got home tonight it only dieseled for a few sec before.
     
  13. AAU54U

    AAU54U Member

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    yes thats a good idea. I'll do that if this continues much longer.
     
  14. grub

    grub New Member

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    mmm now im thinking that your "fuel cleaner" may have dislodged a load of crap from your fuel filter and jammed the injectors open
    maybe change the filter and put a few tanks of fuel it might go away
    a way to check for electrical probs hook up a timing light and see if it stops when you switch off the ignition
     
  15. AAU54U

    AAU54U Member

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    You might be on to something. Will change the filter just in case. The dieseling has improived a lot, now only lasts a second or two after switch off.
     

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