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Timing Light Finds Major Ignition Problems

Discussion in 'Technical Q&A' started by donaldh2o, Jan 10, 2004.

  1. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    My 76 308 failed the California smog test so I'm doing a small tune-up: new plugs, new plug wires, adjusting the carbs and setting the ignition timing.

    Having difficulty getting the timing set. The car is backfiring a bit through the carbs and idling rough. And I'm convinced it is the dwell on the points because it was running better than this before I readjusted the points (single points).

    In the process I discovered a great diagnostic tool: The Timing Light!

    In addition to using the light to set the ignition timing, it can be used to test the operation of the whole ignition system, i.e., is there spark at each cylinder and is it intermittent or not.

    Simply attach the inductive pickup to each of the spark plug wires, pull the trigger and watch the light flash. If it flashes regularly at all 8 cylinders then the critical elements (points, rotor, distributor cap, coil and wires) are likely working okay.

    On my car, on bank 1-4 all cylinders flashed regularly (at 1000 rpm) exept #1, which was intermittent. So I figure maybe the dwell is off or I have a bad plug wire.

    Will know more later, still working on it. But I thought I would pass this little garage knowledge on before I forget it.
     
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  3. ricrain

    ricrain Karting

    Nov 1, 2003
    195
    Dallas Area
    Full Name:
    Ric
    Also, you can fire it at some point on the cam shaft or front crank, regardless of which cylinder and still tell if the timing is regular. Hold the engine at idle or a constant speed after warm up is done. You may not have a reference mark, but irregularities on the cam or crank should appear as "still" images, and not going too far forwards and back. If you get a "blinky" image of rotation, that doesn't seem at all consistent, then you may have a sticking point or other mechanical anomoly. If you get "missing frames" (i.e. irregular interval), check the plug, wire, cap, etc. for defects. As you slowly rev the engine up, the image should appear to rotate, as the centrifugal advance moves the timing up (i.e. more advance for more RPM).
     
  4. 208 GT4

    208 GT4 Formula 3

    Dec 27, 2003
    1,717
    Brighton (UK)
    Full Name:
    Dan
    I'd just like to say thanks to Donald for this tip.

    I've just managed to fix an intermittent loss of power at high rpm on my 208. Following his advice, I purchased a timing light and was able to deduce that No 8 cyl wasn't firing consistently, and the timing of No 7 cyl kept jumping to a different position at about the same frequency as the other was missing.

    From this I deduced it was cross firing and after replacing the leads and cleaning up the contacts on the distributor caps, the car is now running normally again, and idling better than it used to.

    The total cost was to sort the problem was £80 plus I now have my own timing light!
     

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