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Connecting oscilloscope to car ignitions

Discussion in 'Electronic Basics' started by RKovach, Nov 27, 2003.

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  1. RKovach

    RKovach Guest

    I have read that you can use a lab scope to check the secondary firing
    patterns by connecting an inductive lead to the coil wire on #2 channel, and
    connecting another lead to the #1 spark plug wire on #1 channel, and use it
    to trigger the signal. This will show all the plugs, in the firing order, in
    1 trace.
    Can this somehow be used on a distributorless ignition system that does not
    use 1 coil for all the plugs? Is it possible to use 5 pickups, for a 6 cyl.
    engine, all wired together, and connect this to the #2 channel and connect
    the #1 as above to get the same results?
  2. Bob Grimm

    Bob Grimm Guest

    I assume you are referring to DIS (Direct Ignition) as oposed to COP
    (Coil-on-plug) (another form of DIS) Ignition.

    Unfortunately no you cannot just hook up 6 (for a six cyl) inductors
    and view a readable pattern. Most DIS ignition systems fire the
    coils in pairs with the secondary voltage travelling thru the current
    cylinder to be fired and "returning" thru it's companion cylinders
    plug/wire and back to the coil completing the circuit.

    Unless it is an Automotive Scope that can be configured to handle/
    filter that reverse polarity waste-spark you will not get an accurate
    display of the firing lines.

    This is also why a conventional rpm inductive pickup reads 2x
    the acutal rpm when clipped to a DIS wire, since it reads that extra
    waste-spark firing (during the cylinders exhaust stroke).

  3. I'm trying the same thing. My problem how do we capture infrequent events if
    we're using normal scopes. If you succeed, please let me know. How does a
    capacitive pickup work or an inductive lead? Anyone know?

    Here take a look: This is a capacitive pickup which connects around the
    insulation of an ignition circuit component such as a plug wire for scopes.

    Secondary Ignition Pickup

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