TR 1991 Car Judders / Hunts when driving with accelerator pedal pressed at 5% of travel | FerrariChat
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TR 1991 Car Judders / Hunts when driving with accelerator pedal pressed at 5% of travel

Discussion in 'Boxers/TR/M' started by samsung, Sep 1, 2024.

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  1. samsung

    samsung Rookie

    Mar 8, 2011
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    Steve Roberts
    #1 samsung, Sep 1, 2024
    My 1991 Testarossa Judders / Hunts when driving with accelerator pedal slightly pressed in position at about 5% of travel.

    So for example if travelling at 70mph (UK speed limit on motorway) in 5th gear and I press and hold the accelerator pedal in the position of only 5% of the full travel the car is hunting / juddering.
    It drives as if i am stabbing the throttle.

    If i change down to a lower gear for example 4th and I hold the accelerator pedal in the same position at 5% of travel it will do the same.

    When this happens and i press harder and move the pedal past that zone and its fine.

    It does the same when in first when slowly driving away and judders with slight throttle...

    So its an issue relating the the accelerator pedal position

    Any ideas?
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    #2 Steve Magnusson, Sep 1, 2024
    Can you better describe what TR you have (it got pretty weird at the end of TR production in Europe). Engine family F113A (K-Jet) with no cats and no O2 sensors, F113B (KE-Jet) with no cats and no O2 sensors, a CAT version with cats and O2 sensors (KE-Jet with Lambda), etc.?

    About the only thing directly related to the acc. pedal position is the throttle microswitch. One test you could do is just unplug the throttle microswitch and see if it makes any difference in the behavior -- the idle speed will increase, but it shouldn't hurt anything for a brief test.
     
  3. Veedub00

    Veedub00 F1 Veteran
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    #3 Veedub00, Sep 1, 2024
    Mine did that because the timing was off and when the vacuum on both sides wasn’t balanced
     
  4. turbo-joe

    turbo-joe F1 Veteran

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    #4 turbo-joe, Sep 2, 2024
    this would be the easiest and fastest way to find out.
    as I see it the engine is running to lean with this little pedal push of 5 % . you also have this problem when the engine is cold or only when warm?
     
  5. TestaDDS

    TestaDDS Karting

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    #5 TestaDDS, Sep 2, 2024
    Your topic is interesting. Mine (F113B KE-Jet with no cats and no O2 sensors) experiences the same issue between ~1500 RPM and ~2000 RPM. A Ferrari specialist suggested a possible air intake leak (which I haven't found), and a KE-Jet specialist pointed to SP98 fuel not being ideal for 1980s engines at low RPMs.
     
  6. samsung

    samsung Rookie

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    #6 samsung, Sep 2, 2024
    Last edited: Sep 2, 2024


    My Car is a 1991 Engine F113 B (Serial Number 26867) KE Jetronic with no cats and no Lambda sensors. (Tubi Exhaust Fitted by previous owner).

    1. The issue occurs when the car is cold or hot it has the same issue at cold or when warm..
    2. The fault is 100% consistent (at 5% throttle) The issue never not happens when driving and i think its getting slightly worse (The on off judders are harder)
    3. After 5 years of ownership the issue started about a year ago and is getting worse

    What I have noticed is if I reach into the engine and activate the throttle from on top of the engine as I open the throttle I hear one microswitch click followed by the second one (Not quite at the same time)

    Regarding your test if i disconnect the throttle microswitch can i drive the car to actually do the test?

    Thanks
    Steve
     
  7. samsung

    samsung Rookie

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    #7 samsung, Sep 2, 2024

    Interesting.
    Ive purchased a KE Jetronic book from amazon today.

    Do you know how to balance the Vacuum?
     
  8. samsung

    samsung Rookie

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    #8 samsung, Sep 2, 2024
    I alway

    I always use Shell super unleaded (E5) fuel which i the best i can purchase. It has been happening for a good 12 months now and is slowly getting worse.
    I will check the Vacuum pipes
     
  9. samsung

    samsung Rookie

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    #9 samsung, Sep 2, 2024

    Issue occurs cold or warm it doesn't matter.
    On over run the exhaust pops and bangs a lot as if there is too much fuel.
    People following me do say it smells rich of fuel so I'm wondering if its been set up to run rich to over compensate for another issue.


    Thanks
    Steve
     
  10. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #10 Steve Magnusson, Sep 2, 2024
    This is fairly normal. The idle throttle microswitch should audibly "click" as soon as the throttle plates are opened just slightly, and that switch opening causes a relay in the black trapezoidal box over the RR wheel well to unactuate ("click") to enable the cold start injectors to squirt during cold-running if the throttle is quickly blipped. I'd say that the probability that your issue is related to the car just not been tweaked up properly is far more likely as the others have suggested, but this is an easy quicky test. In fact, if your warm idle 1000 RPM does not increase when you unplug the throttle microswitch at warm idle = that would confirm that your car can't be properly tweaked up as the warm idle adjustments need to be made with the throttle idle microswitch closed (which "tells" the Microplex ignition ECU to retard the ignition timing and the KE-Jet ECUs to limit the swings in the EHA currents applied).

    Yes, it shouldn't hurt anything (other than increase your warm idle RPM).
     
  11. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Steve Magnusson
    #11 Steve Magnusson, Sep 2, 2024
    More signs that it just isn't tweaked-up properly as those are certainly not typical TR running behavior (but could be caused by other more bizarre Gremlins ;)).
     
  12. TestaDDS

    TestaDDS Karting

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    #12 TestaDDS, Sep 2, 2024
    WSM KE Jet
     

    Attached Files:

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  13. TestaDDS

    TestaDDS Karting

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    #13 TestaDDS, Sep 2, 2024
    If this helps
     
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  14. samsung

    samsung Rookie

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    #14 samsung, Sep 3, 2024
    Thanks will have a look.
     

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