Misfire light throttle when cold

[Robotaz]

I have a ‘19 Trail Boss with 5.3L AFM and it has developed a slight misfire under light throttle pulling away from my driveway when cold. Does it other times now when cold. I don’t notice any problems at other times. No dash lights. I put Heet and a fuel system cleaner hoping it was water or something. No effect.

 

My first GM and only 1400 miles.

 

It’s going to be a major hassle taking it back and forth to the dealer over and over. I’m hoping someone’s been through this to maybe better focus the service writer and techs.

 

Thoughts?

[ShamrockShooter]

Does it only do it when you lift you foot off the gas and start to coast?

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[ShamrockShooter]

Also try putting it in manual 5th gear which should disable cylinder deactivation assuming you have the custom with a 6 speed. See if it's just that you feeling

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[Robotaz]

Also try putting it in manual 5th gear which should disable cylinder deactivation assuming you have the custom with a 6 speed. See if it's just that you feeling

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Oh I can feel that. It’s not AFM.

This is in first and second gear pulling away from the driveway or my parking spot. Throttle on, but lightly. Only cold.

[BlancoSilverado]

6 minutes ago, ShamrockShooter said:

Also try putting it in manual 5th gear which should disable cylinder deactivation assuming you have the custom with a 6 speed. See if it's just that you feeling

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If the motor is cold it shouldn't be deactivating cylinders?

[Robotaz]

It’s not cylinder deactivation. It’s either a tune problem, coil, MAF, etc. No codes though. I wish it would just throw a code so I could drop it off for a known repair.

[Robotaz]

I made an appointment to drop it off next week and then come in the next morning to drive it with the advisor. I’m trying to stay optimistic but I’m honestly very disappointed in my first GM. I don’t really have time to deal with this right now and it makes a stressful time a lot worse. I hope they can fix it.

[Robotaz]

I’m reading about 5.3L octane, RVP, octane tables, etc.

 

I’m wondering if anyone has enough experience, or read enough around here, to comment on whether me putting last tank of 93 octane in and going back to 87 could cause an issue.

 

I wonder how long the octane tables take to reset. Also curious if this kind of minor hesitation is common with newer 5.3 and especially on winter gas.

 

I think I’ll pull the battery ground off tonight and see if resetting the ECU helps. Sounds desperate right? lol

 

[ShamrockShooter]

Are you using top tier gas or the cheap unbranded stuff?

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[Robotaz]

Are you using top tier gas or the cheap unbranded stuff?

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I used 93 shell and then dropped back to Kroger 87 because I had $.50 off. I’ve had a lot of cars and none would ever respond in any way to that other than my Type R.

Is the 5.3 fairly sensitive? I’ve never owned or driven one.

[SquireSCA]

As a rule of thumb, I use 93 in my 2019 Trail Boss, as well as my 2018 Z71...  The 2018 has a 93 octane performance tune in it, and out of habit I just use 93 in the new truck with a stock tune as well.  While the manual says that regular gas is fine, I have read too many people say that their truck seems to run better/smoother with 93...  On some vehicles, it truly doesn't matter, but perhaps on some it does.

[ct_corey]

my truck does the same thing.  dealer claims that these truck always are on the verge of misfiring due to how lean they run to conserve gas and be emissions compliant. I've tried multiple tanks of 93 and it doesn't change. Dealer says truck operates normal....

 

[Robotaz]

I appreciate you guys taking the time to reply. I’ll stick with 93 gas and just let it warm up in the morning. I doubt the dealer will find anything.

I wonder if the brake recall is a flash for the ECU or just some brake module.

[SquireSCA]

Latest recalls were for the brake thing, as well as the seatbelt pre-tension unit possibly causing a fire in the event of a crash and it deploying...  I haven't heard anything about a recall for an ECM update related to how the motor runs...

 

[Robotaz]

I haven't heard anything about a recall for an ECM update related to how the motor runs...
 

Yeah I’m just wondering if the brake software is part of the ECM tune. Used to brake software went to its own module, similar to the tranny.