Check Eng Light - Scanner shows #6/#7 cylinder misfires?

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ColesRAM

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Need some help from the expert here…….
My son’s 2020 1500 Classic “check engine light” came on the other day. He thought it was the fuel cap since he just filled up. He re-set the cap and the light went off. The following day the light came on again and stays on. He did a preliminary scan which showed a P0300 Code —- generic misfire code. Truck runs fine with no noticeable misfires or performance problems. Today he used a friends more sophisticated scanner (don’t know which model) that showed misfire counter at cylinders 6 & 7. The truck, though, still runs fine. My first thought was plugs and/or coil problems or lose connections at those two cylinders … but I’m not sure. I certainly don’t mine spending a Saturday afternoon changing plug/coils with my son on his truck but is that the problem? Any thoughts or ideas to chase would be appreciated. Thanks.
 
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ColesRAM

ColesRAM

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Guess no one’s has had this problem before? Hmmm……..
 

crash68

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People have reported the problem but it's usually just on one cylinder not two.
As mentioned above, start by swapping the coils on those two cylinders with other ones first. Then if the misfires don't move inspect and/or swap the plugs then lastly the injectors for those cylinders. If you pull the plugs, it would be a good time to inspect the cycle with a bore scope. Make only one change at a time so you can determine what the problem is.
If none of the swapping fixes the issue it's time to pull the valve covers and check if the rockers are moving.
 

Sherman Bird

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Need some help from the expert here…….
My son’s 2020 1500 Classic “check engine light” came on the other day. He thought it was the fuel cap since he just filled up. He re-set the cap and the light went off. The following day the light came on again and stays on. He did a preliminary scan which showed a P0300 Code —- generic misfire code. Truck runs fine with no noticeable misfires or performance problems. Today he used a friends more sophisticated scanner (don’t know which model) that showed misfire counter at cylinders 6 & 7. The truck, though, still runs fine. My first thought was plugs and/or coil problems or lose connections at those two cylinders … but I’m not sure. I certainly don’t mine spending a Saturday afternoon changing plug/coils with my son on his truck but is that the problem? Any thoughts or ideas to chase would be appreciated. Thanks.
Misfires are the NUMBER ONE most misunderstood issues, bar none, on automobiles.
First of all, coils do not go bad summarily. They go bad due to, chiefly, high and excessive KV demand from the combustion process at the spark plug gap(s). This high KV demand causes the spark plug(s) to develop tracking of carbon or plasma due to extremely high temperatures inside the combustion chamber.

This is exacerbated in the Hemi due to 2 plugs on a single coil, although both firing events at the plug gaps are under compression pressure, unlike waste spark systems. My experience with continuous ischemic misfires on cars is almost ALWAYS boiled down to a fuel issue or a condition known as "phantom phasing".

P0300 means very little in that it can and does (in my professional experience) get set from, oh, say, a loose bracket or exhaust component. Let's go "Old School" for a moment... want to?

Start the truck and allow it to warm up to over 160 degrees. Let it idle. Get a piece of notebook paper. Go to the rear of the truck and place the paper across the opening of the tail pipe opening. Does the exhaust pulsing cause momentary "suck back" of the paper up to the pipe? (Tries to suck it in for a split second)?

If it does, you have a legitimate misfire. If not, you are VERY likely experiencing phantom phasing or lean misfire due to dirty or bad injectors.

I see this ALL the time. Now, you must distinguish between phantom phasing or fuel issue.

The scanner can get you to the problem, but you still must develop a diagnosis strategy in order to fix the problem.

Phantom Phasing is also known as Electro magnetic Interference (EMI). I just fixed a GMC 5.3L truck this week due to phantom phasing. Good luck!
 

Burla

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It weird, we need some more info. I'd say the first thing I would do is replace the battery. In the cold the battery life is good, but capacity goes to isht, and the hemi requires a lot of amps to start properly. 4-5 seasons up north your capacity could easily be down 50%.

ity-battery-life-compared-at-different-temperature.jpg
 
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ColesRAM

ColesRAM

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We live in Florida, so cold is not really an issue………..
 
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ColesRAM

ColesRAM

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I suggested to my son, that the first thing should be to check the plug and coil leads on cylinders 6 & 7. Make sure they are on tight and not lose. Waiting on his feedback.
 

White six four

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How many miles are on it? If I'm reading it right it still didn't throw a code for the 2 specific cylinders.? If so how many misfires did the scanner say for cylinders 6 and 7? Just a couple on each or a lot?
 
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ColesRAM

ColesRAM

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How many miles are on it? If I'm reading it right it still didn't throw a code for the 2 specific cylinders.? If so how many misfires did the scanner say for cylinders 6 and 7? Just a couple on each or a lot?
Good question. I’ll check with him……
 
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