No spark focus

Discussion in 'Heavy Truck & Equipment Forum' started by GMC guy, Nov 21, 2016.

  1. GMC guy

    GMC guy Hero Member

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    Ok...changed crank sensor and tried it. No start. I swapped coil. Getting some spark. The odd thing is, i couldnt see the spark in my spark tool but when i grabbed the plug wire i got a jolt! I checked coil connector and just power at the center wire.

    Earlier, i plugged in a noid light and there was no pulse. Starting to sound like fuel pump. Although, sprayed gas into throttle and no start. It sounds like it almost starts and like its firing. Pretty confusing.
     
  2. GMC guy

    GMC guy Hero Member

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    I took the line off at the filter. (A little suspicious that there wasnt a pressurized spray when removed). and it squirted a bit into a plastic bottle at ignition on. Then, with car sputtering on its own, kind of running, it filled the bottle in about 5 seconds. That seems okay but a little on the weak side. i say weak because i expected pressure when i pulled the line off
     
  3. billr

    billr wrench Staff Member

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    Try looking for a spark at every plug. Feeling a jolt in your body is meaningless, 1000V will feel fierce, but firing a plug may take more than 10x that. I'm not sure how that spark tester works, but a good spark will jump over 1/2" in free air. Got it? I'm not convinced you have a good spark yet.

    The injectors still don't pulse? 'Noid lights are OK for a quickie test, but you need to use a meter to tell what's missing: power or the grounding pulse.

    Have you taken compression readings? It never hurts to have some assurance the engine internals are basically OK. Is there any history or event that preceded this "no start" condition?

    Lastly, I would check to see that the fuel pump comes back on while cranking. With the uncertainties still remaining about spark and fuel, it would also be nice to think the CKP circuit is working. Got live-data? Another good tool, check for rpm and fuel PW while cranking.
     
  4. GMC guy

    GMC guy Hero Member

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    Okay, drained fuel tank, changed fuel pump, changed fuel filter. Has spark, fuel injectors checked with noid lights. getting pulses. NO START!
     
  5. billr

    billr wrench Staff Member

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    Have you checked compression, tried starting-fluid? Does the spark jump a gap of at least 1/2" in free-air?
     
  6. kev2

    kev2 wrench

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    I am confused - again- ha ha.

    New coil and we now have spark, Noid light is flashing, correct?

    Then fuel pressure or try spraying carb cleaner into TB see if it hits (fires) on the spray.....
     

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