Using the Scanner to detect a cylinder missfire

My 2016 GMC Sierra 5.3 L83, is exhibiting signs I lost a coil pack. It has 44,000 miles on it, but there have been a few intermittent failures of coil packs noted on the internet forums. This just started up a few miles ago. If I am cruising and it is in high gear at low RPM and the converter is locked up, when I try to lug it it will buck. If I keep it up long enough it will set a temporary check engine for misfire. The more moisture there is in the air the more it will act up. It is progressively getting worse. The problem now is which coil pack?

Is there a way to tell reasonably for certain which cylinder is actually misfiring with the scanner?

Are you sure it's not converter surge? If yours is a 8 or 10 speed it might be that... They are bad for it and some trucks do it later in life.. not right off the bat

You can add misfire per cylinder in the scanner.

Thanks, I will give it a try. I am sure the converter isn't chugging. It sets a temp engine misfire. I have the converter locked up pretty good right there and it is a 6 speed. It is something that just started. It's been awesome for 40,000 miles. It is acting like a coil pack. I just don't want to buy 8 of them!

I have this in the wrong area. Should have posted this in the scanner section.

Update: I detected 28 misfires on cylinder #4 on a short run. It would only occur under a few very specific conditions. If you set the cruise at 60 and then hit a slight grade, that squeeze in of the throttle would create the cylinder pressure that caused the misfires. Coil number 4 was going bad. I installed a new coil and it ran great.

Was #4 coil somehow older or lived a harder life than the other seven coils?

Quote:

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Originally Posted by Robert C Morgillo

I have this in the wrong area. Should have posted this in the scanner section.

Update: I detected 28 misfires on cylinder #4 on a short run. It would only occur under a few very specific conditions. If you set the cruise at 60 and then hit a slight grade, that squeeze in of the throttle would create the cylinder pressure that caused the misfires. Coil number 4 was going bad. I installed a new coil and it ran great.

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Hopefully you have AFM disabled. That is how mine started to lose lifters. Any time you start having misfires on 1,4,6,7 you should be suspect.

Hey Robert!
Sorry to come to the party so late. Congrats on figuring this one out. Yep. It happens. The LT83 and LT86 have a TSB for spark plug wires that are not fully seated on the spark plugs as well. I have seen that get by for 50k then cause a scant misfire when lean in quickly.

AFM sure does kill lifters. Seen it several times already, and broken intake valve springs too. Curious how the newer version will be now that they have these lifters on all cylinders. Hopefully, since they continuously vary which cylinder shuts down they won't have such carbon buildup issues.

Robert, If I remember right, you turned off the AFM a long time ago, yeah?

Hello I am sorry, didn't get back to this. I was out for a bit. Lost a family member to COVID-19.

blindsquirel, Coil #4 showed no signs of anything wrong. Interestingly, I changed all the plugs and wires. Some nice NGK's and large diameter MSD wires. I noticed an immediate difference in the way the engine sounded and ran. I tell you it just seemed to run better. I think IARLLC hit it on the head.

IARLLC, good to hear from you! You provided tremendous help! Yes AFM has been off since I brought it home with 18,000 miles on it. 44,000 now and running great with that tune you helped me with. I was getting ready to comment on what I found when I read your note "The LT83 and LT86 have a TSB for spark plug wires that are not fully seated on the spark plugs as well. I have seen that get by for 50k then cause a scant misfire when lean in quickly." . When I was replacing the plugs and wires I found three plugs that the wires were never fully seated on. The plugs at the top wire connection were actually discolored and rusty looking. I wonder now if that wasn't it all along. After plugs wires and a #4 coil, it runs better than ever. I am thinking you are right on IARLLC, I don't think all the plug wires were seated. I kept the coil, it checks OK with an ohm meter. Of course that doesn't mean its any good!

Robert. The problem was the spark plug. The key that gave it away was the moisture in the air. Coils are not affected by moisture. Wires and plugs are. You likely had carbon tracking in the boot also. Any time I have a bad plug as a rule I will of course change them all and also at a minimum new wires. Cheap insurance. I will see if I have a picture of a great example of a plug I can show you.

Thanks for the kind words, Bob. Real good to hear from you. I am happy that you got it worked out.

Best to you and your family!