Hunting a potential vac leak - Non return valves | FerrariChat
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Hunting a potential vac leak - Non return valves

Discussion in '348/355' started by Surfinrich, Jul 19, 2016.

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  1. Surfinrich

    Surfinrich Rookie

    Aug 17, 2015
    16
    UK West Yorkshire
    #1 Surfinrich, Jul 19, 2016
    Hello All,

    I have the dreaded rough idle. It's intermittent and also much less evident when the air pump is running on cold start.
    The pump wasn't actually working, due to the common blown fuse. It's now replaced with a 20a fuse.
    I've read some really informative posts on here regarding tracking down a vac leak.

    My question is regarding the two small check valves, immediately before the rear suction manifold.
    Can they be "isolated" or turned off? The markings on the case seem to imply it can be twisted/turned maybe to close off.

    If this makes a difference, then the vac leak is between the pump and this point.

    Thanks in advance,
     
  2. JoshH

    JoshH Karting
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    May 16, 2016
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    Austin
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    Joshua Hill
    #2 JoshH, Jul 19, 2016
    Last edited: Jul 19, 2016
    You will break the check valves if you try to twist them. Just clamp the soft rubber hoses off with needle nose pliers or vise grips. I doubt you're experiencing a vacuum leak though, they aren't intermittent problems and not heat sensitive.

    You likely have an ignition issue, like aged out spark plugs or ignition wires with excessive resistance, a fuel supply issue like dirty injectors, dirty mass air flow sensor or aged out primary oxygen sensors, or leaking exhaust manifolds.

    The engine management runs a forced and overly rich w/fuel mixture during cold starts, to get the engine started up and stable, as combustion is less efficient in a cold engine. Once it comes up to temp, the primary oxygen sensors enter "closed loop" mode, which means the ECU is now adjusting fueling based off the primary oxygen sensor's air/fuel ratio feedback.
     
  3. Surfinrich

    Surfinrich Rookie

    Aug 17, 2015
    16
    UK West Yorkshire
    #3 Surfinrich, Jul 19, 2016
    Cheers for the reply Josh,
    I have fitted new cats, new ignition leads, new O2 sensors pre and post cat, new thermocouples and also just fitted new Tubi headers, so all those can be ruled out.
    The plugs look in good condition although I can't vouch for how old they are. At the last service they said they didn't need changing, although I've lost some faith in that particular Indy.
    As you can see, the list is quite long!
    This is why I have been chasing a potential vac leak
    Not checked the MAF, or the injectors yet. I will check the MAF with the multimeter at the weekend.
     
  4. JoshH

    JoshH Karting
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    #4 JoshH, Jul 19, 2016
    If the plugs were recently inspected, mileage wise, they should be fine. Have you had an engine compression and leakeage test performed recently? Have the throttles been synched and balanced bank to bank?

    If you have access to a 5gas analyzer, check the HC and CO content bank to bank, that will help you in determining a diagnostic target also, telling you if there is a lean condition or something else.
     
  5. Surfinrich

    Surfinrich Rookie

    Aug 17, 2015
    16
    UK West Yorkshire
    #5 Surfinrich, Jul 19, 2016
    Prior to fitting new cats and sensors, it failed on all gas levels, CO, HC and lambda.
    After the bits were fitted, it only failed on HC levels, the rest were perfect.
    This high HC again pointed me to a vac leak.

    Not carried out compression or leak test.
    If there was a cylinder/valve issue, would it still present intermittent symptoms, wouldn't it just be bad all the time?
     
  6. JoshH

    JoshH Karting
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    #6 JoshH, Jul 19, 2016
    If by intermittently you mean not every time the car is drievn as opposed to intermittently while the car is warm and running, but every time, then I have to answer "no".

    Have you performed other fuel supply checks? Weak delivery will cause high HC. The pump may be getting weak, making enough pressure but not sufficient flow while under pressure. Also, the rubber bits around the fuel pump might have deteriorated and clogged the fuel filter? I've seen these fuel system troubles several times with ferraris that run excessive HC.
     
  7. yelcab

    yelcab F1 World Champ
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    #7 yelcab, Jul 19, 2016
    Have you done a smoke test?
     
  8. SoCal1

    SoCal1 F1 Veteran
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    Jun 14, 2011
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    Tim Dee
    #8 SoCal1, Jul 19, 2016
    The intake on 355's seem to leak all over. All the hoses that go to it and the plenums itself

    Same thing I found on last 2 I tested


    [ame]http://www.youtube.com/watch?v=94Q-rs9bDO4[/ame]
     
  9. Surfinrich

    Surfinrich Rookie

    Aug 17, 2015
    16
    UK West Yorkshire
    #9 Surfinrich, Jul 19, 2016
    I haven't checked the fuel supply components at all. Will check fuel pressure and also FPR's to see if they are dry on the vac side.
    I assume its checking for holding pressure once the pump has primed, with the ignition on and also constant pressure, engine running, at a steady rpm?

    Regarding smoke test, I've only done a really crude one, via smoke machine, blowing into engine bay to see if there's obvious leaking from exhaust components etc.

    Probably a daft question but, do you need to pipe the smoke direct into the vac system?
    If so, where's the best point to start?
     
  10. yelcab

    yelcab F1 World Champ
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    #10 yelcab, Jul 19, 2016
    Pipe the smoke into the intake air plenum.
     

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