#3 Cylinder Misfire Cause Found

[lt1gmc]

My 2019 96K mile Denali 6.2 developed a #3 misfire, first with just a slightly noticeable rougher idle, then later on a stored code and check engine light. Found #3 plug pretty black when the others were normal white. changed plug, swapped wires and coils, checked compression and leakdown (compression ok but took a couple of seconds longer to get to 240 psi), and looked at spark, checked for broken valve pring and rocker operation visually. Misfire count would stop as rpm went over 2000 rpm. Figured must be a leaking injector since the plug was black. Changed out injectors with a 42K mile set out of a corvette that I have put bigger ones in. (6.2 Trucks use the same injector as a 2014 Corvette 6.2). Still missing. Checked compression and leakdown again, 2-3% leakage and is perfect.
Pulled head and found #3 intake lifter had extreme wear on roller (non-afm cylinder), over .035" worn off lifter and who knows on cam lobe. Thus compression was fine but not enough air getting into cylinder due to lift and duration being less than normal but the same amount of fuel squirted in as the other cylinders so rich especially at idle (black plug) but clears up as rpm goes up.
Point other that fyi about non-afm lifter failure is that I also found 4 pushrods with unusual wear on ball at rocker end. Truck has always had oil changed documented on time, engine perfectly clean and as new inside, and oil pressure fine. Is 0-20 oil responsible? I have over 200K miles on 3 different GM SUV's with afm and no issues and always on 5-30 M1 oil.

 

[Cut Wagon]

That is a great question. As new owner of a 19’ Burb, I’m asking myself the same thing about 0-20 vs 5-30.

 

[West 1]

I am not sold on 0 weight oils. Moving parts need protection to avoid wear. Lifters work under heavy loads and will show this faster than many other parts. Personally I will avoid 0 weight even if the manufacturer does not agree. 0 weight helps them meet the EPA mandatory higher MPG numbers, is not necessarily the best choice should you want an engine to last 250,000 miles. 5-30w has been used without issues for at least 30 years now. That says a lot.

 

[lt1gmc]

I am not sold on 0 weight oils. Moving parts need protection to avoid wear. Lifters work under heavy loads and will show this faster than many other parts. Personally I will avoid 0 weight even if the manufacturer does not agree. 0 weight helps them meet the EPA mandatory higher MPG numbers, is not necessarily the best choice should you want an engine to last 250,000 miles. 5-30w has been used without issues for at least 30 years now. That says a lot.

ON swapping out my cam for the non-afm cam and lifters I found 5 pushrod ends at the rocker with unusual wear, and thus the rocker worn as well. At 96K miles with proper oil change intervals and synthetic 0-20 oil, and the engine perfectly clean inside as new, I have to blame 0-20 oil for unusual wear at this point. I've several previous generations, a 09 with 230K, a 13 Denali with 187K, and an 07 Sierra with 200K, all afm operational and no failures or unusual wear. all with synthetic 5-30.

 

[Marky Dissod]

I am not sold on 0Wxx oils. Moving parts need protection to avoid wear. Lifters work under heavy loads and will show this faster than many other parts.
Personally I will avoid 0Wxx oils, even if the manufacturer does not agree.
0Wxx helps them meet the EPA mandatory higher MpG numbers, is not necessarily the best choice should you want an engine to last 250,000 miles.
5W30 has been used without issues for at least 30 years now. That says a lot.

Ever start a car @ -20F? 5W30 & 0W30 may behave similarly out of the bottle, but try again a month later.
After a month of subzero winter temps day and night, the 0W30 engine will make less noise after the first minute of cold startup, compared to the 5W30 engine.
Granted, 0Wxx or 5Wxx is only applicable BEFORE the engine reaches operating temps.
At operating temp (after the first 15min or so), the viscosity before the 'W' no longer applies; the oil's viscosity has become '30'.

Had you written
"I am not sold on xW20 (or thinner) oils ... Personally I will avoid xW20 or thinner oils, even if the manufacturer does not agree.
xW20 or thinner helps them meet the EPA mandatory higher MpG numbers, is not necessarily the best choice should you want an engine to last 250,000 miles.
5W30 has been used without issues for at least 30 years now. That says a lot."
The latter is absolutely true.

 

[West 1]

I worked ski patrol for 22 years so spent many weekends in the cold but not -20. Usually we would get near zero on our coldest days and 5-30 worked fine with no odd start up noises. I should have thought about those in extreme cold. North Dakota, Montana, parts of Idaho etc. I fully understand the need for lighter weights in those extremes. Same for Hot climates, they use oils that do not work in most areas. Phoenix for example where it is 100-120* commonly can run a little thicker oil maybe 10-30 or even 10-40w due to the extreme heat. I was only thinking of my area where we vary rarely even drop to +30* in the winter and only hit 100 a few times in the summer.

 

[Marky Dissod]

I worked ski patrol for 22 years so spent many weekends in the cold but not -20F.
Usually we would get near zero on our coldest days and 5W30 worked fine with no odd start up noises.
I should have thought about those in extreme cold. North Dakota, Montana, parts of Idaho etc. I fully understand the need for lighter weights in those extremes.
Same for Hot climates, they use oils that do not work in most areas.
Phoenix for example where it is 100F-120F commonly can run a little thicker oil maybe 10W30 or even 10W40 due to the extreme heat.
I was only thinking of my area where we vary rarely even drop to 30F in the winter and only hit 100F a few times in the summer.

To be clear, I'd never recommend 5W20 or 0W20, even for colder areas - 5W30 or 0W30 would achieve similar cold start protection.
(I tried 0W20 for one winter, followed by 5W20 for one more oil change. The MpG benefit was too insignificant to convince me against 5W30 ever since.)

For the much hotter climates I'd recommend 5W40, or certain 10W40 oils for older engines that still work or play hard.
(My old LT1 Caprice used 5W30 for the winter, 10W40 for the summer.)

 

[West 1]

I worked a show in Reno one year in January, it was 5* but had a 30 mph wind almost non stop. At the MGM Grand (yep there was one in Reno back in the late 1980's) there were bunches of cars in the parking lot that would not start. I was in a Diesel Suburban K2500 with a 6.2L diesel at that time, had to tow it to a customers business and plug it in for several hours to warm the block to get it started. Once it was running we let it idle in the parking lot the next couple days till the weather broke. We were not prepared for that type of cold. There were even batteries blowing up in the parking lot as people tried to jump start the cars out in that cold. I had made the mistake of parking with the nose of the car facing the cold wind. We live and learn as we go. Even the Reno locals were not prepared for that cold with the wind. Cars were broken down everywhere. If you live in it, you would be prepared but we never saw those extremes locally. I am sure my diesel probably had 15-40W in it at the time.

 

[lt1gmc]

One thing most don't remember about oil viscosity ratings: They are comparing oil protection ratings and not actual pour viscosity. For example Mobil conventional 5-30 oil will not pour at 5F temperatures, but Mobil 1 synthetic 5-30 oil will pour at -25F. Did the comparison in person for oldest son's science fair project. Both 5-30 rated. The cold pour and pumping capability is why I've used synthetic since 1987. Gets to all the engine parts quicker in the cold.