355 sparking frequency from timing light. 99 6spd | FerrariChat
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355 sparking frequency from timing light. 99 6spd

Discussion in '348/355' started by ThomasK, Jul 31, 2022.

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  1. ThomasK

    ThomasK Karting

    Dec 8, 2009
    132
    Houston, TX
    #1 ThomasK, Jul 31, 2022
    Last edited: Jul 31, 2022
    Hi all,
    i have been trying to diagnose some random misfiring. after attaching a timing light to each wire, the frequency of each cylinder is as follows. half the cylinders seem to flash twice as much as the others. i know its wasted spark, but not sure if these results are correct. flicker speed below:
    1:fast, 2:slow, 3:fast, 4: slow, 5: fast, 6: slow, 7:fast, 8: slow.

    im seeing that my #5 flashing is slightly weak or missing at times, more random. i swapped the coils from side to side, plugs and plug wires to different cylinder with no change to how #5 is acting. im doing compression in a few days.

    any ideas? wiring and power to coil/ECU have been verified.
     
  2. ThomasK

    ThomasK Karting

    Dec 8, 2009
    132
    Houston, TX
    #2 ThomasK, Jul 31, 2022
    compression 195-205psi across the board
     
  3. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,681
    #3 Mitch Alsup, Jul 31, 2022
    One source of misfires is a coupling between spark plug wires where the bundle (of 4) enters the bank oil cover.
    Here, all the wires are so close in proximity that any breakdown of the insulation allows for sparks to jump from one wire to another.
     
    Qavion likes this.
  4. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,069
    Sydney
    Full Name:
    Ian Riddell
    #4 Qavion, Jul 31, 2022
    Seems odd that the problem is on both banks.

    It doesn't seem likely that the ECU or the coilpacks are responsible for the odd firing rate. 1 & 4 use the same coil in the coilpack. So do 3 & 4, 5 &8, 6 & 7.
     
  5. ThomasK

    ThomasK Karting

    Dec 8, 2009
    132
    Houston, TX
    #5 ThomasK, Aug 1, 2022
    thanks
    the car runs pretty well, but it just has a random misfire on an unidentified cylinder. just was curious if anyone had timing lights attached to the wires before and what the pulses looked like. i noticed #5 looked more "messy" with the timing light.
    i have kingsbourne wires, plug wire covers are off and im watching for shorts but dont see any, all cables measure 6kohms +- 500.
    im going to use my o scope with inductive pickup to see what the secondary waveforms look like per cylinder. i think the timing light is just giving a clue that maybe the misfiring is happening in cyl #5 because of the random missing flashes and messyness of the timing light output.
    The waveforms on the scope should show me if there is fuel in the cylinder that is burning or not, fuel decreases the resistance between the spark plug airgap and waveform should have lower amplitude.
    ill post my data when i gather it.
     
    Qavion likes this.
  6. ThomasK

    ThomasK Karting

    Dec 8, 2009
    132
    Houston, TX
    #6 ThomasK, Aug 1, 2022
    thats what really confused me. the fact that one pair (5&8 per instance) had different frequency from the light. 5 was fast and 8 was slow. its the same on all the coil pairs. i probably shouldnt trust the timing light 100% and just use my scope.
     
  7. ThomasK

    ThomasK Karting

    Dec 8, 2009
    132
    Houston, TX
    #7 ThomasK, Aug 1, 2022
    tested spark using an actual inline tool. all cylinders fire consistently and at the same frequency even during the occasional miss. time to look at the injectors i think. ive had them cleaned in the past. maybe one of them is acting up.
     

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