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308 QV Hot Start Idle

Discussion in 'Technical Q&A' started by Dopplemax, May 13, 2004.

  1. Dopplemax

    Dopplemax Formula 3

    My 84 308 QV has begun an annoying habit. She starts and runs great when cold, however, once we've run any distance and go to restart it sounds like a cylider or two aren't firing. If I start her with the throttle one-quarter depressed, I can hear it jump past the miss and then run fine. Thoughts?
     
  2. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    Could be many things. Does it take a while to start when hot? If so then it could be fuel leak down or vapor lock. If it is this then it could be your accumulator, check valve, leaky injectors, WUR also could cause this. It is most likely in the check valve or accumulator. The best way to diagnose it is to hook up a CIS pressure testing gauge set. You can shut the valve off to the WUR to isolate the issue and see if it is in the check valve or accum.
     
  3. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
    10,675
    Worldwide
    Full Name:
    Steven
    i have an extra NEW check valve here for a late model 308. lemme know if you need it.
     
  4. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    1,527
    UK
    Full Name:
    Malcolm W
    Agree it's more than likely a fuel pressure problem, here's some data for when you connect the pressure guage:-

    Leakdown test - connect guage, bridge saftey circuit, turn on ignition, and wait until "warm" control pressure is reached (3.4 - 3.8 bar) then turn ignition off. Observe the drop in pressure - minimum pressure after 10 minutes = 1.7 bar and after 20 minutes = 1.5 bar. If the pressure drops off quickly it's more than likely the check valve in the pump, if it's a slow drop in pressure it still could be the check valve and / or the accumulator.


    MW
     
  5. abarthracer

    abarthracer Formula Junior

    Dec 6, 2003
    373
    Falmouth, Cape Cod
    Full Name:
    david S.
    Hello Malcom,
    Could you be kind enough to provide the specs for for a cold start? I have printed out your directions above and will be checking my car this weekend. Thanks for all of your great input and help on this site.
    David
     
  6. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    1,527
    UK
    Full Name:
    Malcolm W
    David,

    Problem with scanner, I will post soon


    MW
     
  7. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    1,527
    UK
    Full Name:
    Malcolm W
    David - here's the info you need :-

    You need to check the thermo time switch, there will be a number on the side to cross reference the chart below.
     
  8. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    1,527
    UK
    Full Name:
    Malcolm W
    2.

    The cold control pressure will depend on the ambient temperature, for example if the ambient temperature is 20 centigrade the cold pressure is 0.65-1.05 bar.

    Use the graph below as a reference.
     
  9. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    1,527
    UK
    Full Name:
    Malcolm W
    3.

    I might as well give you the rest of the data I have so you will then have everything you need for a complete pressure test.

    Warm control pressure (with vacuum) 3.4 - 3.8 bar and 2.7-3.1 bar (no vacuum)

    Primary pressure 4.5 - 5.2 bar

    Injector opening pressure 2.5 - 3.6 bar


    Hope this helps


    MW
     
  10. Dopplemax

    Dopplemax Formula 3

    Thanks everyone. I'll keep you posted.
     

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