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Stumbling Around 3,000 RPM

Discussion in '348/355' started by Rorie, Jun 14, 2014.

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  1. Rorie

    Rorie Formula Junior

    Oct 2, 2007
    459
    Toronto, Canada
    #1 Rorie, Jun 14, 2014
    Noticed that between 2,750 and say 3,500 RPM car seems to struggle under load. Happens at the same RPM range no matter what gear I am in. After a few seconds Check Engine 1 to 4 light cones on. If I drive outside that range car acts as normal and Check Engine light will go off.

    Sounds like back pressure as you can hear car sputtering. Wonder if it can be related to fact I removed the bypass valve.


    Mechanic has liked at it and us stumped.

    Can anyone make suggestions as to wgat else it could be?

    Car us a 1995 F356 Spider. Has Gruppe M Airbox on it. Euro chipped from Ferrari. All these things were on the car a year or so before the car started to do this.

    Thanks
     
  2. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    499
    New Jersey
    #2 ready321now, Jun 16, 2014
    mine was misfiring 2 days prior to my discovering a left side cracked manifold. I had recently washed it and bit of water dripped into the engine bay I thought perhaps it was interfering with the electronics but it has not happened again since I got the manifolds replaced. I am wondering about that chip and the effect it has on the motor. those are just a few things to consider I hope you work this out easily. though I should add that my misfire was happening more in the four to five thousand rpm range
     
  3. cuneo

    cuneo Formula 3
    Silver Subscribed

    Nov 20, 2006
    2,484
    #3 cuneo, Jun 16, 2014
    Are you running factory cats? Might be a big loose chunk in there.
     
  4. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    6,059
    Indio Ca/ Alberta
    Full Name:
    Grant
    #4 taz355, Jun 17, 2014
    I would like to know more about the chip. Did some research on a few and they did not seem worth it. What are the properties or is it just a challenge style fuel map.
     
  5. Evan.Fiorentino

    Evan.Fiorentino F1 Rookie

    Aug 23, 2005
    2,854
    South East Florida
    Full Name:
    Evan
    #5 Evan.Fiorentino, Jun 18, 2014
    Last edited: Jun 18, 2014
    In my experience with removing the bypass valve, I saw a SIGNIFICANT reduction in low end power however the running of the car was otherwise not altered. I would do a smoke test on the headers to see if any additional air is getting in before the 1st O2 sensor, though even then that should only richen the AF/R. Did you pull any pending codes that the computer has?

    Edit : I see she is an OBD1, is it flashing anything at you?
     
  6. Rorie

    Rorie Formula Junior

    Oct 2, 2007
    459
    Toronto, Canada
    #6 Rorie, Jun 23, 2014
    Thanks Evan. I take the car to Alex at Daytona. We installed Fabspeed Headers and Y Pipe, Catbypasses all from you guys. I am starting to wonder if it is a fuel delivery issue. They are going to look at it next week and see if they can come up with an answer. Car is having issues starting on the first two attempts. Third attempt is starts and stalls, Fourth attempt it starts up fine. The range at which the car is running rough is around the range where I am kind of on the gas only slightly. Where as if I am at 2.500 RPM and accelerate hard I can go through the crappy range and hit 4,000 without issue. But in traffic if I find I am between almost 2.750 and 3.250 it takes more effort to pull the car out of the sputter zone!
     
  7. Markphd

    Markphd Formula Junior

    Mar 10, 2012
    713
    #7 Markphd, Jun 24, 2014
    This needs some old fashion troubleshooting.

    It sounds like a closed loop fuel issue to be honest, does it clean up above 4,000 rpm?

    If so, reset the computer, drive it and see how it runs before it starts learning. If this cleans up the problem, then it is likely the ECU learning the wrong information and adjusting the fuel one way or the other way too far.

    Possible culprits include O2 sensors, MAF sensor, temp sensors, etc. All of which can affect the closed loop operation of the ECU (below 4,000 RPM and other conditions typically need to be met that occur with normal cruise operation).

    I am betting that this is what you are experiencing... It could be caused by reversion in the exhaust system drawing fresh air across the O2 sensors as well. My bet is that the ECU is getting bad information and adjusting poorly.

    Mark
     
  8. ShineKen

    ShineKen Two Time F1 World Champ
    Silver Subscribed

    Aug 3, 2007
    20,032
    Southern California
    Full Name:
    Nostradamus
    #8 ShineKen, Aug 15, 2014
    Is this the infamous tune by the guys in Italy who supposedly developed the ecu for Ferrari?

    Any updates?

    How did the car feel aside from the initial sputtering? Vast improvement?
     

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