Jump to content

2015 Sierra 6.2L Engine Issues - Random Misfire at 15k miles

mt_at

By mt_at
in Troubleshooting & Recalls

Recommended Posts

mt_at Enthusiast

mt_at

Posted
Posted

Hello everyone,

 

First time poster here, used to be a member of another forum that really wasn't too useful... I've lurked on here quite a bit and it seems like y'all do things a lot better!

 

Anyways, I replaced my 08 sierra back in May with a 2015 Sierra 1500 Crew/Short All-Terrain with the 6.2, and I've put about 15.5k miles on it since then, and have done some lighting/suspension mods too (pic attached)

 

I've loved the truck so far until yesterday. The day before I drove about 500 miles. It sat overnight (in about 20 degree weather) then I got in the truck the next morning to head to a meeting. About 1/4 mile down the road I started getting a flashing CEL, traction control off light (oddly no DIC messages like service stabilitrak or anything).

 

Truck was running VERY rough and ended up stalling out. I stopped and let it sit for awhile, checked the plug wires (heard of that issue on a friends truck) but everything seemed ok. Tried to start again... it cranked for a full 6-7 seconds (which is way long) and started barely, but sounded like complete sh*t, very rough and on the verge of stalling out (no CEL on, which was odd). Turned it off and called GM Roadside, got towed to the dealer.

 

Talked to the SA this morning, he confirmed "it sounded like complete sh*t" and is throwing the dreaded random misfire code. They called GM Tech Assist and apparently there has been a known fuse block issue of some sort, so that's what they're checking next - which seems like a lazy way to diagnose a misfire issue but whatever.

 

Wondering if anyone has experienced/heard of random misfires on a low mileage gen V 6.2? Really hoping it's nothing major, but I'm second guessing that $50k purchase of my first new rig already...

post-151722-0-00185900-1450391518_thumb.jpg

post-151722-0-00185900-1450391518_thumb.jpg

post-151722-0-00185900-1450391518_thumb.jpg

post-151722-0-00185900-1450391518_thumb.jpg

mt_at Enthusiast

mt_at

Posted
  • Author
Posted

Update from the dealer:

 

No clue what is wrong and are now working with GM Engineers.

 

Electrical/Ignition system Tests fine, but when running the truck it misfires all over the place, every single cylinder had approximately the same number recorded in the ECM... We know it's not bad gas, but they think it's fuel system related.

 

Still, any suggestions or similar experiences (if any) are welcome!

02Sierra_Mark Enthusiast

02Sierra_Mark

Posted
Posted

Hey mt_at - I don't really have any suggestions or similar experiences but I do hope they get your truck fixed quickly. Good luck man!

TJay74 Senior Enthusiast

TJay74

Posted
Posted

I would let them diagnosis it, no one on here is going to be able to armchair QB this one. The GM tech engineers are pretty smart, they know the systems inside and out so as long as the dealership is willing to put the time into the issue GM will get it resolved.

BuyAmericanIron Enthusiast

BuyAmericanIron

Posted
Posted

TJay is right, let GM and your dealer take the time to fix it right. Probably nothing major.

 

My 15 6.2L had a similar issue. It started running very rough shortly after leaving home one morning. Limped it missing badly for nine miles to work. Diagnosed as a failed #3 fuel injector. Injector did fix the misfire. When I got it back, it was disappointing to find a nice chip in the paint on the LF fender. I could easily see where they tried to rub it out but mysteriously forgot to mention it to me when I picked it up. Good luck with your repairs and look your truck over closely before you move it at the dealer. Just my $.02 cents.

mt_at Enthusiast

mt_at

Posted
  • Author
Posted

Thanks for the input...

The truck is at a dealer a friend owns and that I used to work for, so I know all of them well and am confident in how they treat vehicles luckily.

 

If it was a bad injector then it should only be the one cylinder misfiring, at this point everyone wishes it was that simple!

 

Everything they've tested so far has come back normal, and all 4 of their master techs looked at it today. Fuel pump is the first on the list tomorrow (which I think there was a TSB for - if someone has access to it that would be awesome) but so far nobody has a clue.

 

UPDATE: time to tear down the top of the engine. Stopped throwing misfire codes, now throwing MAF and MAP. Tried replacing both parts to no avail, now it's only throwing map but misfiring still. Valve springs are next up, ignition and fuel systems all working right.

pm26 Senior Enthusiast

pm26

Posted
Posted

Unfortunately, random quality control often results in random problems that are so difficult to find. Do they suspect that the AFM crap is causing this? I bet the problem is of electrical origin, mostly likely a bad connection somewhere in the fuse box.

mt_at Enthusiast

mt_at

Posted
  • Author
Posted

Electrical and Fuel systems are working right. Wasn't making noises that would indicate a lifter issue which is the AFM problem, the only thing now would be valve springs or something.

mt_at Enthusiast

mt_at

Posted
  • Author
Posted

Got a call from the dealer - they found the problem. Two bent valves, which is really bizarre.

 

GM is flying 2 engineers out from Detroit to look at the engine after Christmas since it was such a weird issue, but they want to make sure the rest of the engine is ok and it's not gonna be an issue with other engines...

pm26 Senior Enthusiast

pm26

Posted
Posted

Got a call from the dealer - they found the problem. Two bent valves, which is really bizarre.

 

GM is flying 2 engineers out from Detroit to look at the engine after Christmas since it was such a weird issue, but they want to make sure the rest of the engine is ok and it's not gonna be an issue with other engines...

Well, there are known valve issues with Corvette engines, could this be a similar problem?

wrc7732 Enthusiast

wrc7732

Posted
Posted

Would have thought they would've done a compression check before tearing it down and would have identified a bad cylinder or more that way. Would've helped in know which side to tear down.

 

Very odd though to have two bent valves in such a low mileage truck. What's the corvette valve issue the previous poster mentioned?

 

 

Sent from my iPhone using Tapatalk

mt_at Enthusiast

mt_at

Posted
  • Author
Posted

Got back to town and picked it from the dealer yesterday. Apparently it was bad valves and spring on cyl 8 exhaust.

 

Drove about 50 Mi and the CEL is back on. My crappy old code reader doesn't work too well on these trucks, but it looks to be a Catalyst system failure. So going back in today.

mt_at Enthusiast

mt_at

Posted
  • Author
Posted

UPDATE: 3 catalytic converter codes for bank 2. Dealer has ordered, and is going to replace the Cat. Guessing they ran the engine enough while it was misfiring for it to go bad.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • Aimatdeer
      Ac not keeping up

      By Aimatdeer · Posted

      Monday looks like a good day for the dealer to test an ac issue. Hopefully it all turns out good.
    • CamGTP
      Gas Prices

      By CamGTP · Posted

      Paid $2.72 for E85 today.
    • Atlas
      Gas Prices

      By Atlas · Posted

      Welcome back! No, it definitely doesn't pass the sniff test. Even "ceasefire" needs an alternative definition these days.    $5.29 at Kroger today
    • bluev8
      Intermittent no-code issues on 2022.5+ V8 trucks — what did the shop fail to capture?

      By bluev8 · Posted

      That makes sense, and I think you are describing the real product problem. Capturing data is the easy part. If the owner or technician has to manually dig through five minutes of millisecond-level logs, the product has already failed. The device would be at the ECM harness, not at the OBD port, so I agree that data retrieval and event marking need to be thought through carefully. The way I am thinking about the architecture is: The recorder itself should not depend on a phone, app, Bluetooth, Wi-Fi, or cloud connection to capture the event. It should always keep a local rolling buffer and lock the event locally. A button, phone app, or small cabin device would only act as an event marker. If the driver feels a stumble and presses the button 10–30 seconds later, the pre-buffer has to already contain the useful data. For data retrieval, the practical options would be a sealed service USB lead, Wi-Fi download, or a phone/cabin companion device. I would not expect the owner to remove the ECM-side module or work with raw files directly. The cloud or AI side would be for interpretation, not for capturing the event. The truck may have no connection when the issue happens, so the evidence has to be saved locally first. After that, cloud processing could help decode the data, compare it against baselines, and generate a readable report. For the first version, I would keep the automatic triggers conservative and objective: driver event marker bus-off error passive voltage drop / brownout device reset FIFO or queue overflow a normally periodic message disappearing side-to-side communication mismatch, if the topology supports that For “learning normal,” I agree with your point, but I would not want to overclaim it as automatic root-cause diagnosis at first. A realistic first step would be learned baseline comparison for that specific vehicle and operating condition. For example, a value would only be compared against similar conditions: RPM range load / MAP throttle position gear / vehicle speed coolant and oil temperature battery voltage AFM/DFM state, if decoded and validated Then the report could flag things like: this periodic message disappeared compared with its normal timing this value deviated from this vehicle’s normal range under similar conditions the same abnormal pattern repeated after the same type of event the anomaly occurred together with voltage, oil-pressure, misfire, or communication changes But I would still call that “abnormal pattern detected,” not “replace this part,” unless there is enough validated repair data behind it. So the intended product would not be “here is a huge log.” It would need to be an event package: what triggered the capture how much pre/post data was preserved what changed before and after the event whether the device itself reset, overflowed, or saw a bus error selected graphs around the event raw data only as supporting evidence From your perspective, what would make this kind of report useful instead of just another datalog? For example: What are the top 5 parameters or events you would want highlighted first? Would you trust a learned baseline for that specific vehicle, or would you prefer fixed thresholds? How much false-positive flagging would be acceptable before you stopped looking at the reports? What would a one-page report need to show for an independent shop to take it seriously? For misfire, AFM/DFM, oil pressure, or U-code complaints, what would you want the tool to flag automatically?
    • scotthvac.net
      2022-24 halogen - led grille swap

      By scotthvac.net · Posted

      2024 Silverado 2500 HD LTZ grille no camera Parts list   84603331 84913656 84913657 84913654 84913655 84911567 84911568 85646092 85646093 85797921 85797922   11570637  x10-15   grille/bumper bolts 11546500  x10      grille clips 11571006  x10      push/retainer clips 11546454  x6       nut retainers 11611609  x6       M5 bolts 11610700  x6       molding/trim retainers

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...