Silverado missfire ALMOST solved PLEASE HELP
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Silverado missfire ALMOST solved PLEASE HELP Have a 2000 Silverado 4.8 4wd 1500. I have been trying to fix this thing for months now and have checked many things so far. Sorry for the long post just trying to cover everything. The other day I had an idea to wait till it gets dark outside and look under the hood while the engine is running. Sure enough there is blue sparking happening on nearly all of the coils, and it is completely random where the sparking happens, or how often it sparks. One moment cyl1 coil will spark once or a couple times, then coils for cyl 3 and 5 will happen at the same time, then they won't spark for 20 seconds etc... Random. It happens on both sides of the motor, but it seems like it happens a lot less on bank 2. Sparking happens to the left side of each coil, between the side of the coil and the metal bar that goes around the side. Has no codes anymore, it had a small intake manifold gasket leak throwing p0300 but I replaced them no more missfire code. It's not a dead miss, there is voltage jumping around the coils and I don't know why, I checked the grounds on each injector plug and they all have ground. People are going to say replace coils and wires, but the sparking is happing on nearly all of the coils which leads me to think that something else is causing it. I also noticed that if I turn on a blinker or hazards, the battery gauge on the dash jumps down a tick and the gauge moves very slightly with the blink of the blinker. Also the headlights flicker occasionally too. Alternator and battery are fine. It has ABS codes. If anyone has any idea please help me thing is driving me insane, much appreciated
FireCore Spark Plug Wire Hi AJ, yes the above "tech" is about what to do FIRST.
Second, I would install NEW Spark Plug Wires.
What you see is High Voltage current "leak" common with old wires/bad wires.
That current BELONGS inside the cylinder, good for HP/Fuel Mileage.
I fit FireCore Wires, call OR Call Rick@Firecore.
Your coils should be fine, check the A-Bit connector for "Frankenstein" marks.
Lance
Second, I would install NEW Spark Plug Wires.
What you see is High Voltage current "leak" common with old wires/bad wires.
That current BELONGS inside the cylinder, good for HP/Fuel Mileage.
I fit FireCore Wires, call OR Call Rick@Firecore.
Your coils should be fine, check the A-Bit connector for "Frankenstein" marks.
Lance
Thread Starter
Teching In
Joined: Mar 2018
Posts: 4
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Thanks for the help, I will check the grounds although I have been under that hood for a lot of time and nothing seems out of place. I inspected all the coils there's no cracks in them or anything, they all have very similar resistance readings and all of the wires have similar resistance readings as well and they all are sparking the spark plugs, not sure if even wires will do anything. I just would like to know how common it is that pcms go bad on these and what the chances are that my pcm could be malfunctioning and putting too much voltage to the coils
Thanks for the help, I will check the grounds although I have been under that hood for a lot of time and nothing seems out of place. I inspected all the coils there's no cracks in them or anything, they all have very similar resistance readings and all of the wires have similar resistance readings as well and they all are sparking the spark plugs, not sure if even wires will do anything. I just would like to know how common it is that pcms go bad on these and what the chances are that my pcm could be malfunctioning and putting too much voltage to the coils
I've been a tech for 20 years and 99% of the time that I have some crazy hair brained thing going on that just seems impossible it relates to something extremely simple.
Absolutely is NOT the pcm malufunctioning or an over voltage situation happening, that's not how any of this works. Plus I've never heard of one of those PCM's failing, so to answer you it is not common at all and in my time as a tech PCM's fail about 1 in 1 million, so anytime you ever think "it's probably the PCM" stop and look for something else because it's incredibly rare.
The issue could be that the voltage in the coils are shooting the path of least resistance due to a lack of grounding in the block. Or that the wires are really bad and the spark is seeking a different path.
The erratic behavior with your gauges also points toward ground or charging issues.
If you have those replacement style battery cable ends (where you cut the originals off and bolt them on), replace them, they're junk new and only get worse.
Check your body grounds closely as well from the battery to the body.
Check your voltage at the battery with the engine hot and after it's been running a while with headlights and everything turned on
Last edited by 00pooterSS; Apr 6, 2018 at 08:28 PM.
