308FI Weak spark,9.5 volts at coils Help! | FerrariChat

308FI Weak spark,9.5 volts at coils Help!

Discussion in 'Technical Q&A' started by pnorman, Feb 13, 2004.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. pnorman

    pnorman Rookie

    Dec 30, 2003
    I have a weak spark with only 9.5 volts at the coils, 12.5 volts at the battery. Is this coil voltage too low? My plug wires are new, clean rotors and distributor caps. I have fuel but the car won't fire. Please help!
  2. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    I know little about the ign system on your new-fangled car <g>, but most systems have a resistor somewhere in the primary side of the coil circuit. Check your wiring diagram to make sure. The voltage may be normal.

    Otherwise, do the usual check of wire connectors, fuse/fusebox (if applicable - on my 1975 the ignition doesn't actually flow thru a fuse, but does connect with some other wires at the fusebox), and ign switch. The switch contacts could be providing some resistance.
  3. Mike Florio

    Mike Florio Formula Junior

    Jun 19, 2003
    NW Rural Nevada
    Full Name:
    Mike Florio
    There are two ceramic blocks under the coils. Usually painted red. These are the ballast resistors. Voltage to the coils goes through these resistors. 9.5v at the coil is normal.

    Have you checked your distributors? Dwell, timing, etc? Also the points in the distributor can be adjusted to make sure the spark is delivered to the rotor just when its pointed at a cylinder pin in the cap. It is possible to have the points mispositioned so the spark is delivered to the rotor as much as 10 degrees off.
  4. pnorman

    pnorman Rookie

    Dec 30, 2003
    The 1982 308Fi that I have does not have points or ballast resistors. The timing is fixed controlled by the 2 digiplexes. I don't understand why I have voltage at the coil terminals (the green and yellow wires) but weak spark. The TDC sensors test ok for ohms. The engine died on a couple of occasions before but would eventually restart. Now it won't.
  5. rivee

    rivee F1 Rookie

    Jan 20, 2002
    Nowhere important, USA
    Full Name:
    Check the plug wires at the dist. cap. Sometimes they are not inserted all the way into the terminal. Reinstall after using a little grease on the wires
  6. pnorman

    pnorman Rookie

    Dec 30, 2003
    I'm not getting arching at the coils by running a seperate coil wire to ground, I have 9.5 volts at the terminals.
  7. SR Ferrari

    SR Ferrari Rookie

    Dec 1, 2003
    Keyed voltage at the coil will be 9.5 after it has passed through the resistor.
    With a spark plug , plugged into the plug tower resting it to ground on the motor cranking the motor the spark is decievingly weak but is normal.
    If you want Fried chicken spark change to 2 Bosch blue coils.
    Let the car sit overnight if you have been cranking the car over and over if the plugs get soaked with fuel it will not start this happens with not a lot of cranking.
    Crank motor with no throttle imput.
    Crank speed has to be up as if the battery is weak you will be wasting your time.
    Good Luck
    Kind Regards
    Wayne Hynes.
  8. pnorman

    pnorman Rookie

    Dec 30, 2003
    So with the Cavis wires and extenders and stock coils you shouldn't see a arc to ground? I am getting current to the coils and plugs,just not what I'm use to. I'll keep you posted. Thanks, Patrick

Share This Page