I purchased a 1 owner 2003 Silverado 2500HD 4x4. The person I bought it from put $10,000 into repairs (mechanical - not tires, brakes, etc.) between 2012 and 2018. Seems excessive repairs for a low miles truck. He had all original maintenance records. When I bought the Truck it only had a little over 90,000 miles and came out of San Diego. He is an older gentleman 60's and his home and everything else he owns is immaculate. It was not abused.

I was shocked at the amount of undercarriage rust (Rocker Panels were fine), but everything else appeared to be in really good shape with a maintenance history to boot! I ground off a lot of undercarriage rust and POR15 the hell out of it.

The truck now has 93,000 miles on it. It's my vacation rig and not a daily driver. I love this thing, but I am skeptical about the build quality other than a nice strong frame and pretty comfortable seats.

18,000 miles ago the previous owner had a local Chevy dealer put new Plugs (Iridum NGK TR5IX ) and Wires (Genuine AC Delco Premium Silicone 7mm) and some electrical trouble shooting done and a brand new AC Delco Battery.

I do not drive it much and it has sat over the winter (Startron additive in the Tank) I started it up a week ago and the check engine code came on. I have a basic OBD scan tool and it's throwing a P0300 multi cylinder misfire code. Upon further investigation I have found only the 7th and 8th Cylinder are misfiring. At a ratio of about 3:1 with the worst misfires in Cylinder 8.

I can not see any fluid leaks, I can hear no vacuum leaks, the gas cap is tight. And I just changed the Fuel Filter (Wix straight from O'Reilly Auto via China). The filter was dirty but not full of chunks of crap... just dark brown. No matter how hard I looked I could not find an American Made filter. I read that even AC Delco is China made now and there is a class action over Boxes saying made in USA, but parts stamped Made in China (But that is not what this post is about).

I have never run Iridium plugs before. So I am posting a photo of the plugs straight as I pulled them with no effort to clean them up.

Cylinder #7 Plug has less carbon and looks better
Cylinder #8 Plug has more carbon build up and looks a bit burned

To my eyes while there is some build up of carbon and some darkness they look okay? Why would Cylinder 8 be so much worse than 7 if this were a bad gas problem? Wouldn't other Cylinders also be effected?

I do not know how to troubleshoot this problem. Been doing a lot of searching and reading but still at a loss.

Any Iridium plug experiences... are these okay to just put back in? I have not checked the Gap Spec so obviously I have not gaped them.

I read this comment on Amazon and it concerns me:

"Do not put these in an Escalade !!!!!!! Use AC delco they say they will fit in actuality they will tear your truck up. The misfire is constant and horrible. Paid to have them put In then had to pay to again to replace with ac delco. Not worth the time, money or hassle".

I'm seeing other comments complaining about short life and misfires on Chevys.

Keeping in mind that these were installed by an actual Chevrolet Dealership.

I need to pull one more plug from one of the non-misfires and take a look. I'm thinking about just replacing them all with AC Delco plugs. I drive this rig maybe 2K a year and probably not even that with Gasoline now $5.49 per gallon now.

And what plugs would you all recommend? Should I replace these 2 or just buy a whole new set of AC Delco plugs?



Advice?