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    Author Topic: What do these spark plugs tell you?  (Read 4534 times)

    Offline CudamanTom

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    What do these spark plugs tell you?
    « on: May 31, 2015 - 07:00:29 PM »
    Hey guys,

    I'm still trying to solve my popping/backfire problem from last year.
    Here is that link - http://www.cuda-challenger.com/cc/index.php?topic=100501.0
    I even swapped carbs.
    So today I did a compression test and as I pulled each plug, I noticed 6 & 8 are nice, the others aren't lookin so good.
    The tips on a couple of them seem white-ish.
    I'm guessing 6 fowled plugs?
    So what does that tell me?
    I installed new plugs and wires last summer.
    Running Holley 850 DP. Not sure of the guts.
    AFR is around 14-ish at idle and 12 to 13 when peddle action.
    I wrote the compression reading (cold crank) next to each plug. All with cranking 8 compression cycles during the test. Is this a clue to something?

    Thank you in advance for your thoughts.  :wave:













    Tom
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    Offline acudadude

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    Re: What do these spark plugs tell you?
    « Reply #1 on: May 31, 2015 - 07:14:43 PM »
    # 6 = lean condition or water entering cylinder ie coolant?
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    Offline mopar jack

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    Re: What do these spark plugs tell you?
    « Reply #2 on: May 31, 2015 - 08:13:50 PM »
    Read through the previous post and saw no mention of spark plug wires. I would check the routing and make sure number 6 and 8 aren't crossed. The number 6 plug is not burning and looks to clean. If the intake valve is not opening i.e. the cam lobe is flat there will be no fuel to burn. I doubt the cam is flat because  you will hear a lot of valve train noise and the push rod would be bent or not connected to the rocker and you probably would not have a good compression reading.
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    Offline jhaag

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    Re: What do these spark plugs tell you?
    « Reply #3 on: May 31, 2015 - 11:01:24 PM »
    I would agree that 6 and 8 are not firing. Others appear on the rich side. Compression test should have all cylinders within 10%. Looks close. Looks like an electrical issue to me.
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    Offline hooD

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    Re: What do these spark plugs tell you?
    « Reply #4 on: June 01, 2015 - 01:50:09 AM »
    Check the inside of your distributor cap for all the contacts being corrosion free.  How's the rotor looking? 
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    Offline CudamanTom

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    Re: What do these spark plugs tell you?
    « Reply #5 on: June 01, 2015 - 07:04:16 AM »
    Some good thoughts here.
    I will verify the wiring is in correct order and check the distributor cap & rotor.

    I forgot to mention it's electronic ignition with a MSD 6A system.
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    Offline Chryco Psycho

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    Re: What do these spark plugs tell you?
    « Reply #6 on: June 01, 2015 - 08:51:51 AM »
    possible vacuum leak through the brake booster , too rich overall but 6&8 are lean , using a hotter plug might help
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    Offline dfrazz

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    Re: What do these spark plugs tell you?
    « Reply #7 on: June 01, 2015 - 09:01:48 AM »
    Quote from: CudamanTom on June 01, 2015 - 07:04:16 AM
    Some good thoughts here.
    I will verify the wiring is in correct order and check the distributor cap & rotor.

    I forgot to mention it's electronic ignition with a MSD 6A system.

    Its pretty obvious when the wires are crossed as you should hear a significant miss or even a backfire.
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    Offline HP_Cuda

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    Re: What do these spark plugs tell you?
    « Reply #8 on: June 01, 2015 - 12:03:13 PM »

    Based on your AFR readings it would seem you have a electronic issue.

    What kind of coil are you using with the MSD 6A box? And/or maybe a good time to replace plug wires.
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    Offline CudamanTom

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    Re: What do these spark plugs tell you?
    « Reply #9 on: June 01, 2015 - 01:00:59 PM »
    Quote from: HP_Cuda on June 01, 2015 - 12:03:13 PM
    Based on your AFR readings it would seem you have a electronic issue.

    What kind of coil are you using with the MSD 6A box? And/or maybe a good time to replace plug wires.

    I'm using the MSD Blaster 2 coil. Also, I just replaced the wires last summer and probably have maybe 10 to 20 hours of total run time with the new wires and plugs.
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    Offline CudamanTom

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    Re: What do these spark plugs tell you?
    « Reply #10 on: June 01, 2015 - 01:02:42 PM »
    Quote from: dfrazz on June 01, 2015 - 09:01:48 AM
    Its pretty obvious when the wires are crossed as you should hear a significant miss or even a backfire.

    I do get random backfire/popping when starting out in 1st gear or reverse (under a load)
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    Offline CudamanTom

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    Re: What do these spark plugs tell you?
    « Reply #11 on: June 01, 2015 - 01:03:25 PM »
    Quote from: Chryco Psycho on June 01, 2015 - 08:51:51 AM
    possible vacuum leak through the brake booster , too rich overall but 6&8 are lean , using a hotter plug might help

    I don't have a brake booster.
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    1971 Cuda 440-727 - (clone)


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    Offline HP_Cuda

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    Re: What do these spark plugs tell you?
    « Reply #12 on: June 01, 2015 - 01:37:07 PM »

    Tom

    Is the Blaster 2 coil mounted horizontally or vertically?

    B



    Quote from: CudamanTom on June 01, 2015 - 01:00:59 PM
    I'm using the MSD Blaster 2 coil. Also, I just replaced the wires last summer and probably have maybe 10 to 20 hours of total run time with the new wires and plugs.
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    Offline CudamanTom

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    Re: What do these spark plugs tell you?
    « Reply #13 on: June 01, 2015 - 05:46:52 PM »
    Quote from: HP_Cuda on June 01, 2015 - 01:37:07 PM
    Tom

    Is the Blaster 2 coil mounted horizontally or vertically?

    B

    B,
    I had it horizontal at first then read about it should be verticle (pointing up) so it's been verticle most of the time.
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    1971 Cuda 440-727 - (clone)


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    Offline CudamanTom

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    Re: What do these spark plugs tell you?
    « Reply #14 on: June 01, 2015 - 07:28:05 PM »
    Quote from: mopar jack on May 31, 2015 - 08:13:50 PM
    I would check the routing and make sure number 6 and 8 aren't crossed.

    Well Jack nailed it.

    I verified the wiring and  :banghead: :bricks1: :pullinghair: :banghead: :bricks1: :pullinghair:
    They were crossed. :walkaway:

    So I feel like a total idiot for something so easy and I should have checked a long time ago. :banghead: :bricks1: :banghead: :bricks1: :banghead:
    Funny thing, because it has a cam, I guess the lumpy idle seemed almost normal and I was surprised how well it did run with these two crossed. Which is why I assumed the wiring was correct and ran too good to be incorrect. At least in my mind it did.

    So I still need to purchase new plugs and will report back here in a few days.

    Thanks to everyone and your thoughts and inputs.  :wave:
    I will keep this for future spark plug issues.

    Tom
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    1971 Cuda 440-727 - (clone)


    Because I like it fast!!!
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