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Mondial losing power at 4000 revs

Discussion in 'Technical Q&A' started by Professor, May 30, 2005.

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  1. Professor

    Professor Rookie

    May 30, 2005
    16
    England
    Full Name:
    Andy
    #1 Professor, May 30, 2005
    I have a 1982 Euro Spec Mondial QV (same as 308GTB) Fuel injection. The engine starts/runs OK except when it gets to 4000-5000 rev when it backfires and there is a loss of power. This occurs both on or off load. Does anyone have any idea what could be causing this problem?
    Any help would be greatfully received.
     
  2. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
    Full Name:
    Verell Boaen
    #2 Verell, May 30, 2005
    On injected cars, backfiring is usually due to excess fuel getting into the exhaust.

    Most likely you've got an ignition problem on one bank.
     
  3. jjstecher

    jjstecher Formula Junior

    Jan 21, 2002
    962
    Rochester Minnesota
    Full Name:
    John Stecher
    #3 jjstecher, May 31, 2005
    I had this problem just lately with the 348 and it ended up being the god forsaken alternator had gone bad. The battery cannot provide enough voltage to provide the right ignition current above 4k RPM's. Just a thought...
     
  4. Professor

    Professor Rookie

    May 30, 2005
    16
    England
    Full Name:
    Andy
    #4 Professor, Jun 3, 2005
    Many thanks for the suggestions. I have tested the alternator, which is OK, as well as fitting a new battery and checking wiring but still no difference although this sounds a likely cause!
    The engine will backfire through exhaust even if throttle blipped to 4000RPM. Have changed fuel filter and used injector cleaner in 1/2 tank fuel. Have checked earthing on fuel pump etc, changed plugs and rotor arms and checked HT leads and caps. Also checked the 3 flywheel sensors which show about 800ohms each. Have also checked, or changed all vacuum hoses and induction gaskets together with stripping throttle butterfly. Have checked compressions on all cylinders which are OK, and non-return valve from fuel tank breather.
    Engine starts well and runs OK upto 4000rpm and I have checked for both banks running OK at low RPM. Could the electronic ignition modules cause the problem? If so how do you check them?
    Any other ideas gratefully received.
     
  5. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
    Full Name:
    Verell Boaen
    #5 Verell, Jun 3, 2005
    Have you pulled the distributors & checked the insides carefully for thin arc-over tracks?

    Yes, an ignition module could cause the symptoms.
    Also could be a coil or it's internal drivers failing at higher RPMs.

    A shop with an oscilloscope could watch the plugs on each bank firing while the throttle is reved up. One of the more definitive tests to see what's going on.
     
  6. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    #6 snj5, Jun 3, 2005
    more usual suspects:

    plug extenders - check for small pinhole burn throughs.
    look at the plugs - one or more may be different giving you a clue.
     
  7. Professor

    Professor Rookie

    May 30, 2005
    16
    England
    Full Name:
    Andy
    #7 Professor, Jun 7, 2005
    Raaah!

    Slow drum roll please

    It's fixed!

    After stripping/cleaning/inspecting fuel system/plugs/leads/coils/caps/(even valve timings) etc. etc. The problem was the wiring loom between the tachymetric sensor (rear of engine) and the electronic ignition module. I previously unplugged all three sensors and had a good reading but the molded connector (or should that be a 'disconnector') had an internal fault. Consequently when the engine reached 4000RPM it thought it was flat out!

    I also took the opportunitiy to dismantle the ignition modules as they are exposed to vibration, heat and water (good design Ferrari) and cleaned away all the corrosion with an air line and metholated spirits and soaked both modules in WD40 overnight. I replaced the backplate screws with nuts/bolts and new gaskets. Mondial now running better than ever! (whatever happened to magnetos?)

    Thanks for all your help - will be back on-line with (inevitable) next problem as soon as it appears!
     

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