lean afr

Discussion in 'Technical' started by shineyzx, Dec 8, 2014.

  1. shineyzx

    shineyzx Member

    Hey, im doing some work on a lady's 300. It had a miss which was fixed by replacing the ptu and a coilpack. Once that was done i pluged ecutalk in and its showing a constant lean mixture.
    after a quick read on here would replacing the pressure reg be a good start?
    Faults are temp and i got 1 knock fault after a fair few starts and revs.

    Thanks
    ben
     
  2. East Coast Z

    East Coast Z Well-Known Member

    What was the cause of the misfire?
    The PTU?
    Or the coil pack?
    Is this a "swap out parts until the problem is fixed" diagnosis?
    If you suspect the lean condition is related to a fuel pressure regulator problem, wouldn't a fuel pressure test be warranted?
    What makes you suspect it's a fuel pressure regulator problem?
     
  3. zx299

    zx299 Well-Known Member

    Clear the fault codes.......

    Fix all the sensor problems before you start worrying about mixture, otherwise you'll just be 'chasing your tail' :eek:

    If it still runs lean, start investigating O2's, injectors, vacumn leak.
     
  4. QLDZDR

    QLDZDR ID=David

    Has the battery been disconnected (while you have a beer) after you swapped out those parts to give the ECU a chance to reset?
    [​IMG]
     
  5. shineyzx

    shineyzx Member

    The ptu failed when i was diganisong the miss workig, when replaced there was weak spark on a coil, swaped with one of my owb and the miss was fixed. Then checked for faults the next day (waiting for the cable) .
    Never disconected the battery but car was turned off.
    replacing the coolent sender today.
     
  6. Fists

    Fists Well-Known Member

    The Z ecu learns (slowly) based on feedback from O2 sensors and knock sensor, if the miss had been there for a while it would have leaned out the mixture due to unburnt fuel, unplug the battery for 10 minutes and it will forget its correction map giving you a clean slate.
     
  7. lakerzx

    lakerzx New Member

    actually the opposite happens. if there is a missfire the o2 will read lean which will cause the ecu to add fuel to try and compensate. id start by checking for vacuum leaks, restrictions in the fuel system or a faulty o2 sensor
     
  8. WhiteNight

    WhiteNight Littering and...

    It should be lean unless your on the throttle.
     
  9. NewKleer

    NewKleer Active Member

    the lean is a lean/rich interpretation of the narrowband o2 sensor. best way to work out if its leaning out is to get a wideband (and/or dyno session with wideband). the narrowband cant really be used to determine that and it will commonly be 'lean' when not under power anyway
     
  10. ProckyZ89

    ProckyZ89 Senior Member

    How did ecu talk display a "lean" environment.
     
  11. NewKleer

    NewKleer Active Member

    lean/rich comes from a 'register' in the ECU - ecutalk doesnt determine it. Usually if you compare O2 sensor voltage with lean/rich, you will see lean is usually O2 sensor 0v->0.5v and rich is 0.5v+, but occasionally this isnt the case.

    I think it may actually be an indication of what the ECU is doing in terms of controlling fuel trims. e.g. if it says lean then it might be slowly increasing (making richer) the fuel mixture.

    best to log both of them with ecutalk software and graph the results and see if it is just an interpretation of the O2 sensor voltage.
     
  12. A-Bris-Z

    A-Bris-Z Carcraze

    What about a vacuum leak Ben. Could be sucking some unmetered air from somewhere which would cause a misfire if it was bad enough. You wouldn't see the problem at boost as would reverse it to a rich state.
     

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