Silverado Missfire ALMOST solved PLEASE HELP

[Aj2no17]

Hows it going, any help and advice is VERY much appreciated.

2000 Silverado 4.8 vortec 1500 4wd.  I have been trying to figure this truck out for months, shakes at all rpms although certain rpms are worse than others(the missfire) I have replaced intake manifold gaskets, double and triple checked vaccum system for leaks doing smoke tests (no vaccum leaks), replaced pcv valve, thoroughly cleaned injectors, confirmed everything fuel wise is working properly, new fuel filter.  Still shaking badly.  The other day I had a great idea, I waited until it got dark outside and decided to run the engine and look under the hood.  Sure enough, I noticed sparking (shorting out) happening on pretty much all of the coils.  The sparking is COMPLETELY random and there is never a consistent spark, for example one moment coils for cyl# 2,5,1,7 will be sparking, the next moment they wont and others will, and sometimes they look like they arent sparking at all, Also may mention that the drivers side of the motor seems to be sparking more often but it does indeed happen on both sides. It seems to spark a little more frequently when you spike the throttle.  All i have replaced in the ignition system is the spark plugs, and made no difference at all. All of the coils are producing a spark at the spark plug. I have checked the common grounds to each ignition coil (plug on the top of the coil) and they all were grounded. Truck has 240k miles. If someone could please help me I would really appreciate it I feel like im SO close to fixing this thing and is my only car right now and need to figure it out.  Thanks

[sefiroxx]

Replace the wires? Use dielectric grease to insulate

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[silveradosid]

if you see sparks i would change wires first double check you got the right plugs you might also have some cracked coils

[Aj2no17]

7 hours ago, silveradosid said:

if you see sparks i would change wires first double check you got the right plugs you might also have some cracked coils

Yeah I'm going to start off with wires, I feel like if I replaced all the coils they would start sparking again, I want to figure out if my pcm is voltage overloading the coils or not. All other sensors are working properly 

[Aj2no17]

Anyone else?

[sefiroxx]

No overcharge on modern auto ignition. The 12V on the coil is supplied via the battery and controlled by the pcm. The pcm stops the supply of v and the magnetic field around the coil collapses creating a focus energy on the 2nd coil - increasing the voltage on the second coil.

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[Aj2no17]

On 3/30/2018 at 2:05 AM, sefiroxx said:

No overcharge on modern auto ignition. The 12V on the coil is supplied via the battery and controlled by the pcm. The pcm stops the supply of v and the magnetic field around the coil collapses creating a focus energy on the 2nd coil - increasing the voltage on the second coil.

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Sorry didn't really follow the part about the energy being focused on the second coil but your saying it's not possible for the pcm to be causing this? What could it be other than coils? I'm doing the wires today

[sefiroxx]

Most pcm ignition controls have the pcm switching the ground side of the coil circuit. Ie, battery to fuse to coil to com to ground. Standard physics for electricity passing through a wire creates a magnetic field around the wire. When the wire is wrapped around a core, the magnetic fields of all that wire is focused (think electro magnet). Turn off the power, and that focused magnetic force collapses in a way to induce voltage on a wire (high school science, run a curricular magnet along a wire and it creates a small voltage, a big magnet creates big voltage OR modern regenerative motors on electric cars have a wheel driving a magnet about a wire to create electricity (at a certain voltage) back to the battery usually when braking or even coasting

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[Aj2no17]

5 hours ago, sefiroxx said:

Most pcm ignition controls have the pcm switching the ground side of the coil circuit. Ie, battery to fuse to coil to com to ground. Standard physics for electricity passing through a wire creates a magnetic field around the wire. When the wire is wrapped around a core, the magnetic fields of all that wire is focused (think electro magnet). Turn off the power, and that focused magnetic force collapses in a way to induce voltage on a wire (high school science, run a curricular magnet along a wire and it creates a small voltage, a big magnet creates big voltage OR modern regenerative motors on electric cars have a wheel driving a magnet about a wire to create electricity (at a certain voltage) back to the battery usually when braking or even coasting

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Thanks for the help that is interesting. However i now figured out that coils are not the problem, i replaced coils and wires and same exact shaking. I still see sparking happening but it happens much less, I see sparking occasionally on coil for cyl 1 and i also see it happen down by the spark plugs randomly too. I looked at my dad's truck which is a 2006 5.3 and I noticed the same sparking! But a little less.. however his truck runs smooth as can be. At this point the only thing I really haven't checked is the compression which I will be doing.. what are the chances I could have something internally wrong causing this at 240k miles? Any other ideas besides the compression?

[sefiroxx]

1)Did you put a timing light on each of the plug wires?
2) With a high end scanner, you can cycle each cylinder on/off while monitoring the idle RPM. It should drop 40-50 when a cylinder is turned off. You should unplug the spark plug or disconnect the fuel injector. If a cylinder doesn't drop rpm's, then you'll need to investigate on more detail. (E.g. Stuck injector)
3) A noid light is used to confirm if an injector is getting a signal.
4) If you have a failed compression, then blow by gases are leaking into the coolant, or are losing coolant or are losing oil through the pcv due to excess oil fumes being pushed to the intake.

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[Aj2no17]

10 hours ago, sefiroxx said:

1)Did you put a timing light on each of the plug wires?
2) With a high end scanner, you can cycle each cylinder on/off while monitoring the idle RPM. It should drop 40-50 when a cylinder is turned off. You should unplug the spark plug or disconnect the fuel injector. If a cylinder doesn't drop rpm's, then you'll need to investigate on more detail. (E.g. Stuck injector)
3) A noid light is used to confirm if an injector is getting a signal.
4) If you have a failed compression, then blow by gases are leaking into the coolant, or are losing coolant or are losing oil through the pcv due to excess oil fumes being pushed to the intake.

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I can unplug any coil or any injector individually and they will all make a difference. I cleaned injectors properly 1 by 1 and checked that they are pulsing, everything fuel wise is working properly I am 100% on that. I did pit a timing light on each plug wire actually and I also did a legit spark test on each coil and it looks like they all have a strong spark. The vibrations are worse/better at certain rpms but it is present at all rpms, it's not like a dead miss like a lack of 1 cyl not firing. I'll try to describe the missfire in depth it's going to be hard but if you were to rest your foot on the gas while sitting in park at about 1300 rpm, the shaking almost pulses slowly... So I'll be holding it at 1300 and you will feel the shaking for about 1 full second, then it will actually smooth out for a second, then shake for a second and keep going back and forth. Happens at any rpm but certain rpms shake less than others and the "pulses" between shaking and not shaking occur for different amounts of time for example if I hold it at 2k rpm it will shake for 2 seconds then smooth out for 2 seconds. Sorry for long message but Im really convinced at this point that this truck is unsolvable

[Aj2no17]

On 4/1/2018 at 12:09 AM, sefiroxx said:

 

 

On 4/1/2018 at 11:12 AM, Aj2no17 said:

Update, I checked compression and all cyl are within 5psi of each other, all between 165-170psi, cyl 4 seemed like it was maybe 163 or so but that's not enough to be worried about - compression is fine. I tried shortening the spark plug gaps while the plugs were out, nothing. I'm completely lost at this point, if anyone has any input id appreciate it a lot, thanks 

[sefiroxx]

WHich plugs are you using. GM changed the spark gap requirements for iridium plugs (smaller)

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[Aj2no17]

On 4/2/2018 at 9:06 PM, sefiroxx said:

WHich plugs are you using. GM changed the spark gap requirements for iridium plugs (smaller)

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They are NGK TR5GP. Nothing ignition wise I replaced such as brand new coils and wires, or spark plugs has affected this shaking at all it has always been exactly the same