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355 ‘97 355 misfire

Discussion in '348/355' started by MartinPO, Feb 11, 2024.

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  1. MartinPO

    MartinPO Rookie

    Aug 28, 2016
    31
    Port Orange FL
    Full Name:
    Martin Clark
    #1 MartinPO, Feb 11, 2024
    I wonder if anyone has experienced this please? 1997, 5.2 misfire on idle after the coldstart ends. It will miss for 40 or so seconds, fire on all cylinders for about five seconds then start missing again. Under load while driving, it runs and pulls fine with no miss.






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  2. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    13,573
    San Carlos, CA
    Full Name:
    Mitchell Le
    #2 yelcab, Feb 12, 2024
    This is what you should do, from easy to hard.

    1. Read the code to see if there is a specific cylinder misfiring. Change that plug.
    2. Perform compression test with warm engine, find the offending cylinder
    3. Check fuel pressure at the rails
    4. Perform smoke test for the intake
    5. Perform smoke test for the exhaust
    6. Read live data from O2 sensors
    7. Change all plugs
    8. Change ignition wires
    9. Change ignition coils
    10. Clean injectors

    Did any work just get done on this car? Like an engine out?
     
    19633500GT and Qavion like this.
  3. bobzdar

    bobzdar F1 Veteran

    Sep 22, 2008
    6,895
    Richmond
    Full Name:
    Pete
    #3 bobzdar, Feb 12, 2024
    Is it throwing a CEL or are you judging by ear?
     
    Qavion likes this.
  4. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    11,230
    CT
    Full Name:
    John Kreskovsky
    #4 johnk..., Feb 12, 2024
    Fuel delivery would be my guess.
     
  5. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,312
    Sydney
    Full Name:
    Ian Riddell
    #5 Qavion, Feb 12, 2024
    Would this suggest a problem with closed loop operation (i.e. a sensor or evap system issue) or is perhaps heat causing an issue? At wide open throttle some sensors are not used, so perhaps that’s why the car is ok under load.

    Can you identify which bank the misfire is on? Unfortunately, with a 5.2, you’re limited with respect to what you can swap between banks for diagnosis purposes. Do you have a scanner?

    Are your CEL and Slow Down lights working?
     
  6. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    504
    Chicago IL
    #6 Zamboniman308, Feb 12, 2024
    Grab your Long term fuel trims on each bank while plugged in.
     
  7. MartinPO

    MartinPO Rookie

    Aug 28, 2016
    31
    Port Orange FL
    Full Name:
    Martin Clark
    #7 MartinPO, Feb 13, 2024
    Thank you for your help! 7, 8, 10, all performed, I believe it's been misfiring since an engine out.
     
  8. MartinPO

    MartinPO Rookie

    Aug 28, 2016
    31
    Port Orange FL
    Full Name:
    Martin Clark
    #8 MartinPO, Feb 13, 2024
    Very possibly a sensor I feel, thank you. Both CEL and SDL lights work, but are not activated with this fault. Scanning will be next, thank you for your input!
     
  9. bobzdar

    bobzdar F1 Veteran

    Sep 22, 2008
    6,895
    Richmond
    Full Name:
    Pete
    #9 bobzdar, Feb 13, 2024
    If no CEL, it might be the ITB's out of sync and not a misfire. I'd use an IR thermometer and check the temp at each exhaust flange and see if you actually have a cylinder missing or if it's just a choppy idle.
     
    MartinPO likes this.
  10. squid

    squid Karting

    Oct 5, 2006
    153
    #10 squid, Feb 14, 2024
    Check for codes. On my 1995 cleaning the MAFs cured the cold weather studder.
     

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