Vortec 5.3 Spark Plug Colors

[josef47]

My silverado from 2011 has now run 100000 mls. I changed the spark plugs 300 miles ago. Now i looked at the plugs again. One of the plugs, the one from cylinder 6 is black. All the others are clean. The engine doesn't have any problems. No oil consumption absolutely nothing it hasn't always done. Does anyone have any idea why the plug from cylinder 6 looks so completely different? I am grateful for any hints

[richard wysong]

possibly partialy clogged injector. try a couple tanks of non ethanol fuel with Techron injector cleaner

[CamGTP]

 Cylinders 1,4,6,7 are AFM cylinders, so that may be a reason.

 

You could bore scope a few cylinders to see if they look the same. But I kinda agree, toss some seafoam in the tank or a fuel system cleaner to see if it helps. Obviously move that dirty plug to a different cylinder.

[josef47]

thanks for the food for thought .

Should the AFM be the cause, are there no alarms on the dashboard?

Will a failed cylinder not be displayed to me? 

[mjm-1957]

Look at the center electrode porcelin, its not straight and square like the others. I would replace that plug with a new one put it back in number six and run it for a while and then check again. We have been getting alot of defective AC delco parts right out of the box lately. Possibly a boot leg knock off counterfit  part.

[swathdiver]

8 hours ago, mjm-1957 said:

Look at the center electrode porcelin, its not straight and square like the others. I would replace that plug with a new one put it back in number six and run it for a while and then check again. We have been getting alot of defective AC delco parts right out of the box lately. Possibly a boot leg knock off counterfit  part.

So many counterfeit 41-110s that GM released new part number.  Chicom knockoffs have been wrecking engines left and right, don't use them unless bought from dealer, Summit, RockAuto, etc.  Lots of Chicom plugs sold on Amazon and ebay.

[josef47]

Now i have tried the old spark plugs (50.000mls) i have cleaned them and drove 100mls. everything looks fine now. no black colour on spark plug no 6. Now i will buy again some new spark plugs. It looks like one of the new ones was junk. thank you, BR Josef   

[richard wysong]

I'm curious as to why you pulled the plugs in the first place after changing them. did u have a misfire?

[josef47]

the reason is as follows. I had recently removed the spark plugs after 50000 miles. ( as a routine, no trouble) In doing so, i realized that the color of one of the 8 spark plugs was very light. There were also some small white spots on it. However, i was not sure from which cylinder i had removed it. I wanted to see how the new spark plugs looked after 300 miles. I found this one black spark plug. This was the beginning of my confusion. But now i see that everything is fine. It is probably only one of the new plugs that is not quite right. I am replacing it now. 

 

[Supreme Pizza]

When I have an issues on one cylinder - I check the compression on that cylinder. (100lbs minimum for it to fire reliably). Then I swap the fuel injector, spark plug, spark plug wire, and ignition coil to another cylinder. If the problem follows the parts, then you know its either fuel, or spark. So then you move the injector again to the next cylinder, and see of the problems stays with the ignition parts or follows the fuel injector. Its just as effective as "throwing" new parts at the truck, but its free and much less time consuming. I tracked it down to being a bad spark plug and/or a bad spark plug wire on a PT Cruiser the other day (check engine light, accompanied by a P0303). I replaced them both just to save time. I had both on hand, so why bother testing any further. Then I cleared the codes, and it was good to go. Swapping injectors and coils around sounds hard to some people, but its not. You only need a couple basic hand tools and 10 or 15 minutes of time.

Edited December 17, 2021 by Supreme Pizza

[josef47]

thank you supreme pizza. that is a very good strategy. I will follow if i have got some trouble like this in future. best regards Josef