I've replaced the plugs in our 2007 Yukon (5.3L) in July 2019. I'm posting a picture of the plug comparison at that time showing the before and after. Today, I took at look at cylinder 1 and I noticed the same behavior. The plug tip appears to have melted. Anyone have a suggestion why? So far Google has not returned any good results.

The vehicle is totally stock, other than a tune to eliminate the DOD feature.

One post I found said putting too much anti-seize on the threads insulates the plugs and they could run too hot. This is certainly possible. I usually put a dab about the middle of the threads and then let the twisting of the plug during installation spread it.

 

They're overheating.

Either for some reason they're running extremely high timing, or it's running very lean?
There's no way that the dab of anti-seize found it's way to the tip on all spark plugs.

Also, look at the threads themselves. They are coated with either oil, or dirt. If oil - I'd suspect there are misfires during operation (oil finding it's way to the combustion chamber) So it leads me to ask:
How is the truck running? Smooth? rough? vibrations?
Then, there is the possibility that those threads are black from temperature, meaning those plugs are just too hot. But I suspect that's the least likely possibility here anyway.
If it's just dirt - make sure you're torquing them to spec.

Who did your DOD tune? Or did you do it yourself? What was changed?

What anti-seize are you using? It's possible that particular anti-seize just turns black from heat (mine doesn't though).

 

They also look like it's too lean.

Use silicone dielectric grease on the threads instead of anti-seize.

 

I appreciate the replies. To answer your questions:

Problem: I have had an issue with a slight stumble at idle but it isn't consistent nor have I have been able to narrow it down to weather/operating temps/moon phase. It drives me absolutely nuts but the wife is blissfully ignorant of it. During driving either in city or highway traffic, I don't get any issues that I can tell by the seat of my pants.

Steps I have taken to throw money at it with plugs being the first step have been:
- Plugs
- Intake Gaskets (trying to see if it would resolve a lean issue)
- Fuel Pump (vehicle has 180K miles so figured what the heck)
- Replaced drivers valve cover (resolved oil consumption issue)

Long story short, I replaced injectors with rebuilt injectors from an eBay seller. I tried two different sets from them and got the same issue. As soon as I put in their injectors, I'd have hard start issues if it ever sat and watching the fuel pressure it would drop quickly after turning the vehicle off. After extended time periods it would take 6-7 seconds to start before it would prime and start. This was after the fuel pump. I gave up and just returned them and I'm running to my knowledge the original injectors.

As for the tune, I had a local tuner shop do it. XP Racing in Oklahoma City.

I've been curious about the cats wondering if they are clogged but I'm not getting any codes between the two oxygen sensors indicating any imbalance. Maybe it doesn't work that way. Also, I'm always hesitant to mess with exhaust bolts unless I have to. I have a fear of breaking a bolt. Unfortunately, if it isn't apparent by now, I don't have any sophisticated software to read values. It may just be time to take it to a professional and see what they can find. The do it yourself in me has stopped ,me up to this point hoping there was an easy $100 fix I could try.

 

"Stumble" is usually a pretty reliable indicator of a lean condition. I'd go back and visit the tuner. Especially if you told them you were looking for gas mileage... they might have reached just a bit too far in that direction.

You can soak your injectors yourself overnight in lacquer thinner or MEK or acetone, and it will clean them up somewhat. Nowhere near as thoroughly as a "professional" backflush while held open and then replace the screen; but it will generally "help" somewhat. You'll need new O-rings of course.

 

"I've been curious about the cats wondering if they are clogged but I'm not getting any codes between the two oxygen sensors indicating any imbalance".
^^Where I'd start.

 

So a few updates. I remembered my father in law bought me a FIXD scanner for Christmas and I hadn't really used it. I hooked it up to bank 1 to view the short and long term fuel trims. Surprisingly, the long term ran from -8 to -10% and then the short trim was in the 5-10% range. With the long term in the minus 10% range, that would mean it's getting too much fuel and trying to lean it out, right? The bad part is this tool doesn't let you capture the data anywhere for further review. It is only real time which is a challenge if you want to do any driving to see what it does under load.

And as fate would have it, the last two days after it sat overnight (we haven't been driving hardly any because of the Covid-19 pandemic) it has hard started, taking 6-7 seconds. And when you do it has a fuel smell from the exhaust.

My next step is to validate fuel pressure. I'm not sure if there is a place to effectively clamp the fuel line to the tank but I want to check to see if it is the injectors or the fuel pump check valve bleeding off. With the smell of fuel after starting up my hunch says it is the injectors.

I found this article and thought it did a good job explaining how to interpret fuel trims. If you have any other favorite reference sites, please share.

https://www.autoserviceprofessional....t-work-for-you

 

The long-term trim is more sensitive, and designed to compensate for, things like injector selection, long-term life at altitude, and fuel pressure variation; the short-term targets things more transient that that but not "instantaneous" like throttle position, like driving up and down mountains, fuel variation, and ambient temp & humidity.

Gotta always remember though, the ECM can't INDEPENDENTLY "see" what's going on. It's ONLY "eyes" into the matter are the O2 sensors. Once those start not telling the truth, all bets are off as to what the ECM will "see" and as a consequence what it will do. If yours are old and haven't ever been replaced, might want to consider changing them.

 

You nailed it!
ECM knows NADA without its army of sentries I MEAN sensors standing watch on the perimeters.
Sorry, just a little levity... but it is mostly accurate.

 

What type of plug? Miles?

 

They are AC Delco Iridium plugs 41-110. I don't know on exact mileage but I swapped them in July 2019, so they can't be anymore than 15,000 miles.

 

The pictures didnt load the first time. The orange on the straps gives me pause. Are you using some kind of wacko fuel, or additive? That's not normal. $3 TR55 or TR6 plugs will outperform the iridiums, if you dont mind changing them every couple years - and they won't melt.

 

At one point I ran some Redline fuel cleaner but other than that, just plain old 87 octane from the local gas station.

I may have to give the TR55 a try. I just need probably a year or two more out of this vehicle before we get something newer.

 

Just to close out this thread for future searchers, I took the vehicle for a diagnostic checkup.

Before I went in, I replaced the spark plugs with the NGK TR55 plugs and put on new wires. It didn't fix the issue but seems to run a little better.

As for the diagnostic results, they couldn't pinpoint any issues. The fuel trims were running they said at 10% but for the age and mileage of the vehicle, not concerning. They did reset everything just as a precaution so the computer could relearn. The plugs they said in their opinion were from oil fouling. Therefore, nothing to fix when you weigh the price vs. age of the vehicle. At this point I'll live with the slight stumble at idle and change plugs more regularly.

 

Appreciate you updating this. Most threads never get updated with a conclusion, and are dead ends. Makes it aggravating for the person searching Google, and never finding an answer.

 

Based on condition of plugs, they misdiagnosed the root cause of your vehicle stumble. Oil fouled would not burn the center electrode off. Only serious heat or serious spark will. Don't think anti-seize is going to impact plug temp that much. Each plug thread is locking into threads of head when torqued to 15ft lbs. Personally, anti-seize is not needed on GM LS engines. Ford 3V 5.4 with 2 piece plug, yes.

Any pending, history or current codes stored in PCM? What did previous plugs look like? How many miles were on them? The recent plugs (12621258) with 15K look like they have 150K on them. When did the off idle stumble start?

Need to find a shop that can datalog/record fueling parameters to see what's going on when driving. Was +10% at idle or cruise? It's needing to add fuel to hit target AFR. Idle indicates possible vacuum leak. Cruise idicates fuel delivery. Fuel pressure low? Do you experience detonation when vehicle is hot or under load (going up long/steep hill)? Are you using a K&N filter that is depositing oil on the MAF? MAF or IAT could be off. Lot's of things to look at to help pinpoint root cause. You need an excellent diagnostic tech that go through the process to resolve your issue.

 

I'll show you exactly what the problem is... : https://www.alibaba.com/product-deta...OI&bypass=true
Buy your parts from Authorized GM Parts Dealers Only!!! https://sdparts.com/

 

I apologize. Apparently I have not setup my notifications. I randomly opened this thread and saw the additional comments.
The issue only appears to happen at idle. While driving I do not seem to get any drivability issues that you can feel. With a data logger, obviously you could get the nitty gritty detail. I have a cheap bluetooth scanner that can give live data but it doesn't record it, so it makes it hard to really diagnose.

If there is detonation, I can't tell. I don't hear pinging or anything like that. I'm using a stock air filter. I've identified I have the common broken exhaust manifold bolt issue (3 so far that I see). I plan to swap out plugs when I have everything out just because of the ease of access.

Here lately, I'm occasionally getting hard starts like the fuel has bleed off. The fuel pump is new within a year so I don't think it should be bad (integrated check valve). I just need to get a fuel pressure gauge on it to see what it is doing. It isn't consistent so that makes it all the more fun to troubleshoot.

 

You have knock off plugs with chinesium electrodes, not true iridium, that's why they wore out so fast. The same way copper plugs wear out in 30k or so miles vs 100k with platinum/iridium, that cheap metal wore out way faster than the real thing would have.

As for coloring, those look like almost every plug I pull out of a car (I'm a tech and do plugs multiple times a week). I see plugs in bone stock vehicles a lot and they almost all have that brownish color. (Oddly mine do not, but I see it A LOT on customer cars, always assumed it's due to fuel or some sort of fuel additive?)


Edit: I ordered a real one, here's a video of it.
And for guys saying it's too hot, when I melted plugs in the past I melted the ground electrode off, not the center electrode.. is melting the center electrode a common thing too?

 

That was extremely helpful. I really appreciate it. I learned something new today so I guess my day is done!