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How do you test the ignition coils?

Discussion in 'Transmission & Drive train' started by sparkone, Mar 30, 2010.

  1. sparkone

    sparkone Active Member

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    How to you test the coils for the one that is misfiring? I plan to change all of them at once, but I still want to know for my own knowing.
     
  2. KWT2000

    KWT2000 Full Access Members

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    the easy way is to pull the codes and see which cylider is missfiring... you can measure the resistance between the points at the plug you should have .3-1.0 ohms of resistance
     
  3. Remo

    Remo Full Access Members

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    Based on my experience with my 2000 5.4:

    If you drive it 3 times (I think) and it misfires each time, the service engine light will come on.
    Then, you can plug a scanner into the OBD II port (under the dashboard, below the steering wheel and to the right) and it will give you a code.
    The code will tell you which cylinder is misfiring.

    If you don't have a scanner, there are autoparts stores that can scan it for free (I know Autozone does for sure).

    Cylinders are labeled 1-8 (obviously). Passenger side is 1-4, driver side is 5-8. 1 and 5 are at the front of the engine; 4 and 8 are at the back.

    Then, remove the coil on plug assembly. It is held in with one bolt, plus an electrical connection and sits on top of the spark plug.

    Once the coil is out, you can check the primary and secondary resistances using a multimeter.
    Measure the resistance (in ohms) across the electrical connector (primary) and from the connector to the spark plug connection (secondary).

    I don't know the specs off hand, but I know they are listed in the Haynes manual.

    From my experience replacing two bad coils, I can say that the resistance can be correct and the coil may still be bad. This is particularly true when the misfire isn't at idle but only under acceleration or load (like going up a hill).

    When you replace the coil, don't forget to use some kind of dielectric grease to protect both of the connections.

    Finally, once it is all back together, it should take 3 cycles of normal driving w/o misfire to turn off the service engine light and clear the code.

    Hope that helps! Goodluck!
     
  4. Remo

    Remo Full Access Members

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    Also, I just remembered:

    New coils at Autozone were Duralast brand and about $50/ea with No Warranty. I've used these so far and they have been fine for the last two years or so (knock on wood).
    Advance Auto had similar prices--maybe a little bit more expensive.

    I think genuine Motorcraft COPs were around $80/ea, last I checked.

    More recently, I discovered that Summit Racing has great deals on COPs. They have COPs starting at $25/ea or less than $200 for a set of 8. I think they were Accel brand and have a 1 yr warranty.
    Plus they have other higher priced performance ones if that is what you are looking for.

    Hopefully that gives you a headstart on your shopping.
     
  5. KWT2000

    KWT2000 Full Access Members

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    the primary resistance is .3-1.0 ohms and the secondairy is 7K-10K ohms...... but as stated a coil with in spec can still missfire soo the code reader is better IMO
     
  6. sparkone

    sparkone Active Member

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    Thanks! I have a Lincoln Town Car also with a 4.6, same setup. I'm getting the Coils off of ebay for $25 ea. free shipping. That's a whole lot better than when I paid $54 ea., from Auto Zone, for the Town Car.
     

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