• Welcome to SVTPerformance!

A/F issue

Discussion in 'SVT Shelby GT500' started by Uae2dec, Jan 11, 2019.

  1. Uae2dec

    Uae2dec New Member

    Messages:
    5
    Joined:
    Jan 11, 2019
    Location:
    UAE
    Good afternoon,

    I have 07 gt500 moded as last 2days the A/F ration dip to between ~ 11.3 to 12 and suddenly to 16 while idling but While I driving the range is fine and also with full throttle.

    anyone face the same


    With regards.
    Abdulla from UAE
     
  2. SCGallo2

    SCGallo2 Balanced performance Premium Member Established Member

    Messages:
    851
    Joined:
    Mar 4, 2014
    Location:
    California, MD
    I have seen a similar AFR indication from an engine cold start while in open loop fueling. A momentary spike to 16 would not concern me in this situation at idle and not under load. Does your engine stumble when AFR indicates 16? Your tuner can adjust open loop fueling tables if it is causing driveability issues until your engine gets up to normal operating temperature and transitions to closed loop fueling. You would need to capture the event in a datalog and forward it to your tuner, or allow your tuner to "drive" tune your car, if possible. It sounds like your normal closed loop fueling and open loop fueling at wide open throttle are where they should be.

    Edit: I am assuming you are running an unleaded gasoline fuel equivalent to 91-100 octane.
     
    Last edited: Jan 11, 2019
  3. Uae2dec

    Uae2dec New Member

    Messages:
    5
    Joined:
    Jan 11, 2019
    Location:
    UAE


    As you said it's stumble when AFR indicates16 and cousing the drivableity issue. But this issue show up after 30 min and forward. If it's only when the engine is cold it will go after minutes. But actually the issue after the driving the car.

    Moreover, I will double check with the tuner.

    Appreciate ur respond
     
  4. 69b302

    69b302 Member Established Member

    Messages:
    398
    Joined:
    Feb 26, 2007
    Location:
    NY
    Check for vacuum leaks. They show up more at idle, when air flow is low.

    my 0.02
     
  5. Uae2dec

    Uae2dec New Member

    Messages:
    5
    Joined:
    Jan 11, 2019
    Location:
    UAE
    I checked this point and nothing show.

    Thanks
     
  6. SCGallo2

    SCGallo2 Balanced performance Premium Member Established Member

    Messages:
    851
    Joined:
    Mar 4, 2014
    Location:
    California, MD
    If your engine is stumbling, then it is actually running lean in that situation which isn't good. And if your main concern is after your engine should have transitioned to closed loop fueling, something is not right. Are you running a large mono-blade throttle body?

    Cold start engine stumbling during open loop fueling is not uncommon with cars running 1000cc injectors or larger. Tuners can adjust fueling tables to achieve acceptable if not perfect driveability, depending on how much focus they put into this area of the calibration (some more than others), because your engine usually transitions to closed loop fueling within a few minutes of operation, where driveability should be perfect... no stumbling and AFR should remain within acceptable limits at all times.
     
  7. Uae2dec

    Uae2dec New Member

    Messages:
    5
    Joined:
    Jan 11, 2019
    Location:
    UAE


    Thank u for this detailes and within coming days the tuner will come to see where is the issue and I will post the outcome from his visit

    It was large mono-blade throttle body but I returned back to 65 mm CJ.

    WHO IS the best online tuniner for the large mono-blade throttle body
     
  8. SCGallo2

    SCGallo2 Balanced performance Premium Member Established Member

    Messages:
    851
    Joined:
    Mar 4, 2014
    Location:
    California, MD
    Mono-blade throttle bodies can be problematic in terms of street driveability which is why most go with a Cobra Jet twin 65mm, VMP twin 67mm, or Whipple twin 68mm for a good compromise between power and driveability. VMP Performance, Lund Racing, and JDM Engineering, to name a few, should all be able to remote tune a "known good" Ford Racing Super Cobra Jet mono-blade throttle body. Lund Racing seems to have the Kenne Bell 168 mono-blade figured out, and if you need that big of a throttle body, that's the route I would take. I am perfectly content with my CJ twin 65mm for high performance street/road course applications. Personally, I would only install a mono-blade for max effort drag strip action.
     
    Uae2dec, HillbillyHotRod and moncho like this.
  9. moncho

    moncho Active Member Established Member

    Messages:
    401
    Joined:
    Oct 12, 2011
    Location:
    Out West
    Great advice Steve!
     
  10. Uae2dec

    Uae2dec New Member

    Messages:
    5
    Joined:
    Jan 11, 2019
    Location:
    UAE


    Great advice
     

Share This Page