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Thread: No Spark # 7

  1. #1

    Default No Spark # 7

    Hi everyone, first post here hoping you guys can help me out.
    I have no spark on # 7. have put new plugs, wires and a coil on that cyl but still no spark when testing with a timing light and I get a random misfire code. Is there a common problem that would cause this issue? I see no problem with the wiring. Thanks for any responses.

  2. #2
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    Default

    with any problem you have to say what vehicle, year, engine , and all the other info about your vehicle...

    if no spark on one cylinder and you have a 5.3L engine my guess is no power to the coil.

  3. #3

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    Quote Originally Posted by j cat View Post
    with any problem you have to say what vehicle, year, engine , and all the other info about your vehicle...

    if no spark on one cylinder and you have a 5.3L engine my guess is no power to the coil.
    Yeah, so sorry `07 Sierra 6.0 L. Just stared out of the blue driving down the highway. Totally stock. With the timing light hooked up # 7 does flash, but only like once or twice every 10 seconds or so. Tugging on the wiring harness doesn't really change anything.
    Last edited by Rukee; 11-15-2013 at 07:02 PM.

  4. #4

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    as @j cat stated you may not be getting power to the coil. Check the resistance of the coil. Did you actually check for spark with a tester on that coil? After that its gotta go back to the juice getting there.
    David
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  5. #5

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    Random misfire sounds like more than one cylinder not firing. Check out this video it has several items to check or replace.

  6. #6

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    Quote Originally Posted by Rukee View Post
    Yeah, so sorry `07 Sierra 6.0 L. Just stared out of the blue driving down the highway. Totally stock. With the timing light hooked up # 7 does flash, but only like once or twice every 10 seconds or so. Tugging on the wiring harness doesn't really change anything.
    Does it have AFM? I seem to remember that #7 turns out to be an issue with AFM.

    1995 Silverado 4x4
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  7. #7

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    Sorry, what is AFM?

  8. #8

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    Quote Originally Posted by Rukee View Post
    Sorry, what is AFM?
    Active Fuel Management. When the load on the engine is light, four cylinders are essentially shut down. When the load increases they're re-activated. There is a solenoid that open and closes the oil port to the valve lifter that locks or unlock the lifter. In the lock mode the intake and exhaust valve remain closed, therefore, no fuel to ignite. I'm not sure if the ignition coil is also deactivated, if coil is turned off, the ECM may be shutting it down when its not suppose to. The engine will normally operate on 8 cylinders in V8 mode during starting, idling, and medium or heavy throttle conditions. It's possible that the AFM is the root
    cause.

    AFM explained here http://www.gm-trucks.com/forums/topi...how-afm-works/

    Read it here for a little history of cylinder deactivation. http://en.wikipedia.org/wiki/Active_Fuel_Management

  9. #9

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    Thanks for that, but reading that thread it states it's only deactivating the lifters, not the coils, so I'm thinking I have something else going on. If it was the AFM, then I would still have spark at idle like the rest of the cyl's.

  10. #10

    Default

    Quote Originally Posted by Rukee View Post
    Thanks for that, but reading that thread it states it's only deactivating the lifters, not the coils, so I'm thinking I have something else going on. If it was the AFM, then I would still have spark at idle like the rest of the cyl's.
    Is sounds like there are no "check engine" or other warning indicators and posting here also seems you don't want to put down a bunch of bucks at a dealer repair shop (I don't blame you). There are several national wide auto parts stores that will plug in your OBD II port and read any codes that might be stored AND they do not charge you. Of course they prefer that you buy the repair parts from them. It's worth a shot. They usually will not clear the codes, if any.

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