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2020 Already Missfiring

2020 Already Missfiring

Postby JetBlackZ28 [OP] » Jun 06 2020, 3:34pm

I posted this on another GM Truck Forum, but figured I'd share it here.

Was driving and then my CEL started to flash and then my dash said to get the Parking Brake Serviced and the ESC(?) System Serviced, after a minute or so everything went back to normal and all lights went off. Took it to the dealership later that week and all they could see was a misfire code. They stated everything looked good and all the computers in the truck were running the most up to date software. And they couldn't get the truck to duplicate the problem. They told me they called GM HQ to see if there was any new/unreleased info on the truck, but there wasn't.

I asked why it showed servicing those systems if it was just a misfire that prompted the CEL to flash. They said it was probably a power/voltage surge through the system that just accidentally triggered some sensors.

I have a 2020 Silverado LT All-Star Edition, 5.3 with 8 speed and just over 5k miles
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Re: 2020 Already Missfiring

Postby GBSierraSLE » Jun 06 2020, 7:52pm

Well that stinks. Hopefully it was just a hiccup or glitch and won't ever happen again.
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Re: 2020 Already Missfiring

Postby EaOutlaw1969 » Jun 06 2020, 9:28pm

Have you gone through heavy rain with deep puddles at any point since you have had the truck . I can see a temp misfire happening under these circumstances causing weird things to happen especially with the tons of sensitive electronics onboard.

If it was my truck and is was out of warranty I would inspect the High voltage leads to the spark plugs and make sure they have some dielectric grease in the boots.

But since it is under warranty it is probably best to leave it alone or they will find away to blame your tinkering.

Yet it does suck anytime a new very expensive vehicle malfunctions it sort of kills the new vehicle experience.

Hopefully it will get worse so they can find and fix the problem, I think that would be better than for it to never happen again as it may leave you always wondering when it will happen again.
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Re: 2020 Already Missfiring

Postby JetBlackZ28 [OP] » Jun 06 2020, 9:32pm

I mean the truck sits outside at all times so its constantly getting rained on, I've hit some puddles but nothing to deep.

Yeah since its under warranty and only happened once, I have no intention of messing with it myself.
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Re: 2020 Already Missfiring

Postby MIKE91B » Jun 06 2020, 9:51pm

I see injectors in your future. I have already had to put lifters in a 4.3L 2020 truck. I can’t remover how many miles it had but it was way up there. Like more than 50,000 if I remember correctly. It happens. If it is injectors be aware they are on back order.
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Re: 2020 Already Missfiring

Postby JetBlackZ28 [OP] » Jun 06 2020, 10:29pm

MIKE91B wrote:I see injectors in your future. I have already had to put lifters in a 4.3L 2020 truck. I can’t remover how many miles it had but it was way up there. Like more than 50,000 if I remember correctly. It happens. If it is injectors be aware they are on back order.


Thanks for the heads up but I'm not worried. Trucks brand new with a bumper to bumper warranty. And ill be trading it back in before that ends.
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Re: 2020 Already Missfiring

Postby bclounch » Aug 10 2020, 5:20pm

I just purchased a 2020 GMC Sierra last weekend and have the same issues. Wondering if there were some quality control issues at the plant.
Attached is a data log showing what is going on. I have some serious KR and misfires on Cyl 8 during cruise. Took it in last week for P0300 and they did a cam relearn. Its back at the dealership this morning with the same issues.

Not sure what normal vacuum is for these trucks, but mine does seem to be very low at cruise and idle.
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Data Log.xlsx
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Re: 2020 Already Missfiring

Postby Sector7500 » Aug 11 2020, 12:54am

Similar issue here. 2020 Sierra, only about a month old and about 1200 miles. Flashing check engine light for about 10-20 seconds then it went off and everything was normal. No noticeable misfire but a stored code of P0300 in history. Happened twice in a 3 day period over 300 miles. Returned to dealer twice and basically got a shoulder shrug and computer reset.
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Re: 2020 Already Missfiring

Postby DrLove38 » Aug 12 2020, 8:41pm

I feel for all 3 of you. This stuff is not good for for GM reputation on quality or service. It is really disappointing for me being a lifelong Bowtie guy.
But I won't be going drooling around the dealership like I have been several times thinking real serious about upgrading.
So for now I will just keep my 2003 Silverado SS with 75G on the odometer with a bullet proof 6.o and no serious problems since I bought it brand new.
I can very seldom leave the house that I don't get compliments on it too.
I don't know what to recommend ya'll do about your trucks but I hope you get something resolved or tell them to take it back.
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Re: 2020 Already Missfiring

Postby bclounch » Aug 12 2020, 9:56pm

Stick with LQ4 for sure. Built one for my Trans Am and it has been great!

Update:
Dealer just reset the codes and said they couldn't duplicate the issue. I provided all data logs for them to review.
Did find out that the vacuum readings are normal for these new motors. Was used to seeing vacuum at cruise in my LQ4.

The thing that bothers me is they say the truck is operating normally. I asked about the KR and they said that was normal. No way in hell should 7* of KR at cruise be normal.
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