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Really need help and advise on the strange in 355 (5.2)

Discussion in 'Technical Q&A' started by bigbird, Jan 22, 2009.

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  1. bigbird

    bigbird Rookie

    Apr 19, 2008
    18
    #1 bigbird, Jan 22, 2009
    Need some advise and any experience about my problem in my car F355(5.2)

    The cold start run smoothly till it warms. My engine start to be rough but very strange thing is that when I switch on my A/C, the com kicks on my engine back to be smooth again but when the A/C kick off my car back to be rough again. I tried to figure it out and search in this forum but couldn't find the answer. So if anyone could advise and suggest me how it could happen will be appreciated.

    Thanks in advance.
     
  2. tbakowsky

    tbakowsky F1 World Champ
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    #2 tbakowsky, Jan 22, 2009
    check your o2 sensors
     
  3. No Doubt

    No Doubt Seven Time F1 World Champ

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    #3 No Doubt, Jan 22, 2009
    At what rpm level is your idle when A/C is off?

    At what rpm level is your idle when A/C is on?
     
  4. bigbird

    bigbird Rookie

    Apr 19, 2008
    18
    #4 bigbird, Jan 22, 2009
    I have already changed my O2.
    The cold start my rpm will be around 1000 up,
    But till it get warm
    when my A/C is off it will be around 900.
    when my A/C is on it will be around 1000 up( it seems to have vacumm to increase RPM)

    Thanks.
     
  5. DrStranglove

    DrStranglove FChat Assassin
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    #5 DrStranglove, Jan 23, 2009
    Probably carbon on the values.
     
  6. No Doubt

    No Doubt Seven Time F1 World Champ

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    #6 No Doubt, Jan 23, 2009
    The first thing that comes to mind is that you are running rich (idle air valve opens more when A/C is on, leaning mixture to increase idle speed RPMs), which is fine when your engine is cold, but a bit too much when warm.

    If you had the M2.7 355 I'd suggest resetting the engine ECUs, but I don't know the process for doing that to a 5.2 car. I'd want to try that ECU reset prior to testing (or simply replacing) your multiple engine coolant temperature sensors (a cold signal from a failed temp sensor will cause you to run too rich, for instance).

    Then you'll want to test your fuel pressure regulators.

    If none of the above works, then I'd suggest pulling all 8 spark plugs for review per the link in my signature below. You could also try the "pretend to drive forward against the emergency brake" trick to see if you detect any knocking/thumping/missing or major engine vibrations...but I'd save that sort of test for much later in the diagnostic process (i.e. right before an engine pull).


    Your O2 sensors should be ignored at idle, cold engine, and wide open throttle, by the way.
     
  7. rustybits

    rustybits F1 Rookie
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    #7 rustybits, Jan 23, 2009
    Check the idle speed control valve hasn't popped out of the rubber hose, it causes symptoms as you describe.
     
  8. bigbird

    bigbird Rookie

    Apr 19, 2008
    18
    #8 bigbird, Jan 24, 2009
    I have already changed the idle speed and check all the wiring. It seems to be fine. Anyone know how to reset engine ECU. Is it the one that switch off battery and restart again? If that, I have already dine but not have any changed. Now checking the spark wire but my mechanic said it still looking good. And he also suggest that if problem with spark wire it will rough both cold and hot. Btw I have some misfire also. My car change muffer and test pipe to TUBI. Help!!!
     
  9. saw1998

    saw1998 F1 Veteran

    Jun 8, 2008
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    #9 saw1998, Jan 24, 2009
    The procedure to reset the Motronic 5.2 ECU, is the same as the 2.7. First, turn the battery disconnect off for at least 1 min. Start the car with EVERTHING electrical off (e.g., radio, AC, interior light, etc.). Let the car run for approximately 15 min. at idle.
     
  10. No Doubt

    No Doubt Seven Time F1 World Champ

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    #10 No Doubt, Jan 24, 2009
    Last edited: Jan 24, 2009
    No, the M5.2 computer uses non-volatile flash memory like a thumb-disk drive or iPod uses. You won't erase everything inside it by turning off the battery like you can with resetting the M2.7 ecus by disconnecting power to them.

    The process that you describe above will work for M2.7, but at most on a 5.2 will merely cause the computer to go into adaptive mode. However, eventually adaptive mode will do the equivilent of a reset (could take 50 miles of driving, though).
     
  11. ferrari.ace

    ferrari.ace Karting

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    #11 ferrari.ace, Jan 24, 2009

    The above works for 2.7 Motronic. You can baseline the 5.2 with a Ferrari SD-1 or SD-2
     

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