Rough idle with warm engine /tank ventilation valve | FerrariChat
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Rough idle with warm engine /tank ventilation valve

Discussion in 'Boxers/TR/M' started by plip, Jul 25, 2024.

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  1. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #1 plip, Jul 25, 2024
    Good day all


    1987 TR CH Version with KE-Jetronic.


    Had the engine out over the winter for major service and for replacing Diff carrier.


    Engine back in the car all fine but…. when engine is warm, if shut off and immediately re-start, idle is fine. If car sits say 20 and more min and re-start, idle is rough, like not firing on all 12 cylinders and stabilized after abt 20/30 seconds.


    Do have sparks on all leads (checked each single one with strobe light). Seems like car starves on fuel upon starting. No issue at all when engine is cold. Starts and idle perfectly.


    To be noted that since always had very high pressure in the fuel tank, and therefore the known noise on right side of the car when shut off, have replaced the tank ventilation valve but it did not cure the problem. Had then removed the valve for good. Car does not have charcoal canisters. Just the valve and a ‘silencer’ (??) after the valve.


    Could that be the reason for the rough idle when warm started ?

    Many Tks
    Gianni
     
  2. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,089
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #2 Rifledriver, Jul 25, 2024
    Classic leaking injectors symptom.
     
  3. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #3 plip, Jul 26, 2024
    Many Tks Brian. Will check. Actually all 12 injectors and all OR have been replaced abt 3000 km ago.
     
  4. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,089
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #4 Rifledriver, Jul 26, 2024
    If you think there is a tank venting problem take off the gas cap. If it changes you have a vent problem. If it doesn't you dont.
     
  5. Grease Donkey

    Grease Donkey Karting

    Jul 5, 2018
    120
    Zurich, Switzerland
    #5 Grease Donkey, Jul 26, 2024
    Fuel pumps replaced?

    Connectors on fuse board checked?
     
  6. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #6 plip, Jul 29, 2024
    Yeep no issues. Actually board modified many years ago. All high drawing current stuff not going via the white connectors any longer.
     
  7. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #7 plip, Jul 29, 2024
    Tks again Brian.
    Dunno think is a tank venting problem. Have re-installed the ventilation valve. After driving the car have the 'usual' noise at the right side of the car, meaning the valves is releasing the extra pressure. Same behavior with the valve, or after opening the gas cap and releasing all the pressure inside the tank. Stars rough for some 10/20 seconds and then stabilized. Idle revs slightly lower when rough, then rock solid a tad above 1000 rmp. No issue when driving. Car runs just fine.

    Am puzzled.

    Did not have this issue b4 taking the engine out. All done was cambelt service, replaced the diff carrier , and water thermostats.
     
  8. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,089
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #8 Rifledriver, Jul 29, 2024
    "Rock solid a tad above 1000 RPM"? Where is the idle set?

    "Did not have this issue b4 taking the engine out. All done was cambelt service, replaced the diff carrier , and water thermostats."

    Something was done incorrectly.
     
  9. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #9 plip, Jul 29, 2024
    Obviously. The question is what....but most of all why only when engine is warm. No issue when cold.
     
  10. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,779
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #10 Steve Magnusson, Jul 29, 2024
    One test you could try is unplugging the single wires of O2 sensors (label stuff clearly so they don't get mixed up) before doing the "warm restart after 20 minutes" to see if the problem is still there, or not -- might give a clue if this is the system having trouble running closed-loop in this condition (and it is a difficult condition because the coolant is still warm enough to put the KE system in the warm mode, but the O2 sensors will have cooled off quite a bit -- whereas, the O2 sensors are still "hot" for an immediate restart), or if it is something else.
     
  11. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #11 plip, Jul 31, 2024
    Good day Steve. Many tks. Will try and report back.
     
  12. plip

    plip Formula Junior

    Aug 25, 2003
    292
    Switzerland
    Full Name:
    Gianni Olivieri
    #12 plip, Aug 1, 2024
    Good afternoon Steve. Unfortunately no real improvement with O2 sensor disconnected. Idle still rough after warm engine sits for some time and then re-started. It stabilize and sound better after abt 20 seconds.
    Will keep on digging...

    Tks yrs help. Always appreciated.
     

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