2019 GMC Sierra 6.2 gasoline, periodic rough idle and periodic bluish white smoke exhaust discharge

[Cabe]

I purchased this 2019 new and for the first 50K miles it has had zero issues. After about 55K miles I noticed a slight rough idle like a misfire but it was not 100 % of the time.  After about 60K miles it was more often and every now and then (approx once every couple of weeks, that I would notice) I would see a belch of bluish white smoke at take off, (like from a stop light or stop sign) then it would go away. 

Truck is now at 65K miles and it all happens more often. Yesterday I noticed the largest blech of bluish white smoke as I was driving (approx 50 MPH).

 

Most of the time it does not blech the smoke and it runs great all the time, other than the rough periodic idle.

I've had it into the dealer and they say nothing is wrong (or nothing showing in diagnostics).

We are working thru an oil consumption test as the engine will burn a quart in 1000 to 1700 miles.

 

What I am really concerned about is the belching smoke. Does anyone have experience with this or similar?

 

THANKS, Chris

[JimCost2014]

Direct injections do all kind of fun stuff, including what comes out of the tailpipe, and just the general sound of the engine while it is running. Do a remote start while standing by the tailpipe when it is cold, and report back what it looks like.

[Cabe]

Thanks for the response... I have tried that with nothing to report. I have never had any smoke at start up.

Today was one of the roughest idle days I've had, but no smoke belch as I was expecting to see.

[JimCost2014]

1 hour ago, Cabe said:

Thanks for the response... I have tried that with nothing to report. I have never had any smoke at start up.

Today was one of the roughest idle days I've had, but no smoke belch as I was expecting to see.

I would start with the simple things, are all of the plug wires seated solidly? Have you checked for codes? Could be a fuel injector? Mybe a coil pack?

The oil consumption is probably going to come back deemed as within specs, how long has it been  loosing that much in that mileage frame?

Edited July 21, 2024 by JimCost2014

[Gangly]

With a rough idle combined with blue smoke (indicative of oil) and white smoke (indicative of coolant), I would start checking for head gasket leaks.  A quick check of the coolant reservoir to see if there is any oil or bubbles present, as well as a compression/leak-down check.  Buying used, its possible the vehicle had the heads removed prior to your purchase (lifter issue?), and you might be having issues from that repair process.  I hope its nothing, good luck to you.

Edited July 22, 2024 by Gangly

[Cabe]

Jim... Been thru all that, no codes and the truck still runs great. Has burned a quart in 1100 to 1600 miles since new.

 

Gangly... thanks for the response. I purchased the truck new, this all started at about 55000 miles. Nothing odd about the coolant tank either as I was thinking about that as well. Last week was the most I have seen the smoke. Twice at a start from stop and once while driving. All in four days. Each time a considerable belch of bluish white smoke. Each time only a couple of seconds, but a good cloud.

 

Since the truck is still under a warranty I have been pushing to get them to look deeper. Appears if they see nothing with diagnostics they have nothing to report and they have not seen the smoke, I understand that.

Had different dealers give me different answers about the rough idle too, one said it does not sound right and one said that 6.2's do that... have not been back to talk to him.

 

Like I said the truck runs great... my real concern is the periodic smoke then the rough idle.

 

Thanks for your input.

[silveradosid]

i would look at miss fire counts on all cylinders, next an injector balance test. and last i would be looking at the pvc system which can give a rough idle and the puffs of blue smoke

[Gangly]

You might have significant oil entering your intake from the PCV systems, resulting in oil burn on startup.  When I pulled my intake manifold, there was significant oil coating the inside of the intake manifold, particularly going into the first two cylinders, that was directly related to oil entering the intake tract from the PCV system where it connects to the intake manifold just ahead of the TB (throttle body).  You could see a thin, tan, oil stain stripe on the TB from oil entering the intake via the PCV system.  You can remove the intake tract (air box and piping going to the engine) ahead of the the TB, and look into the manifold to check for oil residue on the TB. 

 

You might have a spark plug that could be worn out as well, getting an insufficient spark resulting in incomplete combustion when cold, but clearing out as the engine warms up.  Its possible, but I wouldn't think so.  Good luck.