No Spark # 7

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Rukee, Nov 15, 2013.

  1. Rukee

    Rukee New Member

    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. j cat

    j cat Active Member

    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. Rukee

    Rukee New Member

    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: Nov 15, 2013
  4. dsfloyd

    dsfloyd New Member

    as [MENTION=39185]j cat[/MENTION] 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.
  5. WorthFlorida

    WorthFlorida New Member

  6. Pikey

    Pikey Moderator Staff Member

    Does it have AFM? I seem to remember that #7 turns out to be an issue with AFM.
  7. Rukee

    Rukee New Member

    Sorry, what is AFM?
  8. WorthFlorida

    WorthFlorida New Member

    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/topic/118710-school-me-on-how-afm-works/

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

    Rukee New Member

    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. WorthFlorida

    WorthFlorida New Member

    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.
  11. Rukee

    Rukee New Member

    I have a scan tool that turns off the CEL, but as soon as the truck runs with the dead miss on #7 for a few seconds, it sets the p0300 code.
  12. j cat

    j cat Active Member

    the p0300 is random miss fires. with this code most times it is a fuel delivery problem low fuel pressures.

    could also be restricted exhaust .

    I missed the random miss fire code mentioned by you . I just saw your #7 cylinder mentioned.

    P0307 is #7 cyl miss
  13. Rukee

    Rukee New Member

    okay, but fuel pressure is not going to kill the #7 coil ! Like I said the # 7 has no spark when checking with a timing light, all other cyl's do.
  14. j cat

    j cat Active Member

    the PCM is not stupid . if you have a miss with the #7 cyl it will say so.

    so what is the fuel pressure ? any other DTC ..
  15. Rukee

    Rukee New Member

    It may very well have more then one cyl miss firing, but # 7 is all but totally dead. The timing light might flash once or twice a minute on # 7. Fuel pressure holds steady at 60psi. No other codes, but the service traction control is flashing in the MC.

    - - - Updated - - -

    I disconnected the coil harness and checked continuity between the harness plug and the coil plug, everything checks out. So now I need to check the engine harness. Does anyone has a wiring schematics for the ECM? There are three main plugs, it would be very helpful to know which plug and pins I should be looking at. Thanks in advance.
  16. Pikey

    Pikey Moderator Staff Member

    just for the heck of it I would switch the #7 coil with a known good coil. See if it is still doing the same thing or if you have a problem with the coil. Just because there is continuity does not mean that the coil is good.
  17. Rukee

    Rukee New Member

    I bought a new coil for # 7. I wouldn't expect 2 coils in a row to be bad. But I can swap it easy enough with the one next to it.

    - - - Updated - - -

    Swapped with the # 5 coil and wire miss stayed at # 7. So I'm thinking engine harness. Like I said earlier, does anyone has a wiring schematics for the ECM (PCM)? There are three main plugs, it would be very helpful to know which plug and pins I should be looking at for that # 7 coil.
  18. j cat

    j cat Active Member

    I have a diagram of the 2000 silverado 6 L engine wiring.

    this shows the black wire A as the ground of the coil. D is the 12 volts to the coil pink wire. B is called the reference low brown wire. and the C is the red wire this is the control .

    B and C go to the PCM ...if you have ground good and 12 volts then you will have to check at the PCM for wire/connector damage..

    B/C are specific to this cylinder. I guess that with a meter you could probe these PCM voltages to see how it is different than the working coils.

    using a O scope would be nice...
  19. Rukee

    Rukee New Member

    Thank you for that. I do have a good ground on the black wire and battery voltage at the pink wire, so now it's down to either the B or C wire are broken, or the PCM is burnt out for the # 7 cyl. Anyone have a diagram for where the B and C wires for # 7 go into the PCM?
  20. j cat

    j cat Active Member

    so with that then remove get access to the PCM check all wires there and remove connectors to inspect for damage/corroded green wires/ rodent chewed etc..

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