Misfire at start up

TJay74 · July 28, 2019

OK to clear you up some, the trucks are an LT series engine. The Corvette and Camaro use the LT1, the trucks use the L83 or the L86. All are direct injection and tend to be a little noisy when running. With that it isnt uncommon for a DI injector to go bad and cause rough running at start up. Typically the bad injector will trip the check engine light and point to which cylinder has the bad injector.

Graphite Silverado 2018 · July 28, 2019

This issue hasnt set off an engine light yet. Dealerships took a look a few times and pretty much me, keep driving dont worry its under warrenty still.

Graphite Silverado 2018 · August 9, 2019

Lapoolboy, so it does idle at about 500rpm. Normally

Silver18 · August 17, 2019

I also have this issue with my 2018 Silverado with the 5.3. Does the same as OP and clears up a bit after a few minutes of driving. Dealership couldn't find amythi g as well.

jay webb · August 17, 2019

On 8/8/2019 at 11:46 PM, Graphite Silverado 2018 said:

Lapoolboy, so it does idle at about 500rpm. Normally

speaking as a tech for gmc dealership. if it is happening on cold start ( after it has sat for hours/overnight) and goes away after warms up. it is a misfire wont always set a SES LIGHT. its called a cold start misfire and it will store a P050D, which is related to the injectors. they can see this with a scan tool as a current or history code. it can also have a history P0300 random misfire. they can look at misfire data from freeze frame to try to see what cylinder, typically they need to have it to cold start to duplicate. we have a tool that is designed to test the injectors called the A FIT . this will isolate what injector/injectors are bad. common issue on the 2014-2018 v8 engines 5.3/6.2. if its out of warranty its typically a 5 hours of labor + parts which is injector(s) , seal kit, and high pressure fuel lines. ( fuel lines are one time use according to gm, they run under the intake to the fuel rails from the high pressure fuel pump.

if you are paying out of pocket ( no warranty ) it would be my suggestion to replace all the injectors in the bank ( or all 8 ) typically they will do this for little to no extra labor cuz they are already in there. but you would have to pay per injector which i think is $150-$200 off the top of my head.

Graphite Silverado 2018 · August 17, 2019

Jay webb, yes thats the exact issue. 4 different dealers have checked it out. Truck is still under warrenty. Only has 14000km on it. Any suggestions on what i can do abiut this? Or if i can mention anything in particular? Will this cause a major issue in the future for my truck if i keep driving it like this?

jay webb · August 17, 2019

On 7/26/2019 at 12:50 AM, Graphite Silverado 2018 said:

Got a 2018 silverado lt with the 5.3l v8. It has 13000km on it. Since new it has been misfiring when starting up in the morning for about 5 mins. Until i get it going and then it runs fine. Pretty much if you leave parked for about 6 hours it will misfire. Took it to 4 different gm stealerships to find out what wrong. Nothing was found but misfire still there. No engine lights or anything on dash. Engine sounds a little rough too. Any ideas on what it can be?

typically this is a cold start misfire , can have codes may not. typical codes would be a P050D associated with P0300 or any of the following P0301-P0302-P0303-P0304-P0305-P0306-P0307-P0308

P0300 is random misfire, P0301 thru P0308 is a misfire with the last digit of the code identifying the cylinder.

codes may be history, might not be current. they can see in history of how many misfires via freeze frame data. and perform an injector balance test. this is most likely related to faulty fuel injector(s).

jay webb · August 17, 2019

14 hours ago, Graphite Silverado 2018 said:

Jay webb, yes thats the exact issue. 4 different dealers have checked it out. Truck is still under warrenty. Only has 14000km on it. Any suggestions on what i can do abiut this? Or if i can mention anything in particular? Will this cause a major issue in the future for my truck if i keep driving it like this?

its just something typical regarding direct injection engines. not sure why the injectors get faulty but they do. ask the dealer to perform an injector balance test and have them keep it overnight for a cold start. explain it happens on cold start. not when the engine is warm/hot.

if they hook up scan tool and start the truck while engine is code and watch the misfire graphic they can see what injector(s) are misfiring, go from there to do a balance test. then the repair.

Bob2C · August 18, 2019

My 2018 Tahoe does the same thing. Idles rough like it’s misfiring at stop light. No codes but it will do it when warmed up. Idles below 500. No issue with acceleration. Dealer says it’s normal for those engines. After reading the posts here, I’m thinking it’s an injector issue. Do I press the dealer or run it until something happens?

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Graphite Silverado 2018 · August 18, 2019

I have the same question as Bob2c, do i press the dealer? Or wait until something happens? Last thing i want is to keep driving it, then then dealer says you should have not driven it if you knew the problem was there.

jay webb · August 18, 2019

9 hours ago, Bob2C said:

My 2018 Tahoe does the same thing. Idles rough like it’s misfiring at stop light. No codes but it will do it when warmed up. Idles below 500. No issue with acceleration. Dealer says it’s normal for those engines. After reading the posts here, I’m thinking it’s an injector issue. Do I press the dealer or run it until something happens?

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alot of these trucks/suv with a misfire/rough idle at stop lights are typically engine mount related

17-NA-166: Rough Idle in Drive - (Apr 18, 2019)

Subject:

Rough Idle in Drive

This Bulletin replaces PIP5211F. Please discard PIP5211F.

Brand:	Model:	Model Year:		VIN:		Engine:	Transmission:
Brand:	Model:	from	to	from	to	Engine:	Transmission:

Cadillac	Escalade Models	2015	2019			L83, L86, LV1, LV3 (4.3L, 5.3L, 6.2L)	All
Chevrolet	Silverado	2014	2018
	Silverado LD	2019	2019
	Suburban	2015	2019
	Tahoe	2015	2019
GMC	Sierra	2014	2018
GMC	Sierra Limited	2019	2019
GMC	Yukon Models	2015	2019

Some customers may comment about a rough idle and/or vibration at idle in Drive.

This condition may be most noticeable following extended driving, after hard acceleration, while idling at a stop in Drive.

May feel like a lopey or lumpy idle, or may be described as a low idle.

This condition will not be present in Park or Neutral. (There have been a few cases for rough idle in Reverse.)

Note: There will not be any DTCs with this concern.

If the rough idle / vibration concern frequency is E1.5 in the horizontal / lateral direction with Pico sensor mounted in seat track as indicated below – continue with steps to install updated design engine mounts and settle both engine and trans mounts to reduce amplitude (mg) / eliminate ground out within the engine mounts for vehicles built prior to engine mount breakpoint. For vehicles built after breakpoint, follow Shimming Procedure for Engine Mount Vibration/Grounding after Mount Replacement.

SO THE DEALERSHIP NEEDS TO EITHER PUT SHIMS OR REPLACE THE ENGINE MOUNTS

Bob2C · August 18, 2019

alot of these trucks/suv with a misfire/rough idle at stop lights are typically engine mount related

17-NA-166: Rough Idle in Drive - (Apr 18, 2019)

Subject: Rough Idle in Drive

This Bulletin replaces PIP5211F. Please discard PIP5211F.

Brand:
Model:
Model Year:
VIN:
Engine:
Transmission:

from
to
from
to

Cadillac
Escalade Models
2015
2019
L83, L86, LV1, LV3 (4.3L, 5.3L, 6.2L)
All

Chevrolet
Silverado
2014
2018

Silverado LD
2019
2019

Suburban
2015
2019

Tahoe

GMC
Sierra
2014
2018

Sierra Limited
2019
2019

GMC
Yukon Models
2015
2019

Some customers may comment about a rough idle and/or vibration at idle in Drive.

This condition may be most noticeable following extended driving, after hard acceleration, while idling at a stop in Drive.

May feel like a lopey or lumpy idle, or may be described as a low idle.

This condition will not be present in Park or Neutral. (There have been a few cases for rough idle in Reverse.)
Note: There will not be any DTCs with this concern.

If the rough idle / vibration concern frequency is E1.5 in the horizontal / lateral direction with Pico sensor mounted in seat track as indicated below – continue with steps to install updated design engine mounts and settle both engine and trans mounts to reduce amplitude (mg) / eliminate ground out within the engine mounts for vehicles built prior to engine mount breakpoint. For vehicles built after breakpoint, follow Shimming Procedure for Engine Mount Vibration/Grounding after Mount Replacement.

SO THE DEALERSHIP NEEDS TO EITHER PUT SHIMS OR REPLACE THE ENGINE MOUNTS

Thanks a bunch. I am going for an oil change next week and will talk to them about this

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Bob2C · September 15, 2019

On 8/18/2019 at 7:03 AM, jay webb said:

alot of these trucks/suv with a misfire/rough idle at stop lights are typically engine mount related

17-NA-166: Rough Idle in Drive - (Apr 18, 2019)

Subject: Rough Idle in Drive

This Bulletin replaces PIP5211F. Please discard PIP5211F.

Brand:

Model:

Model Year:

VIN:

Engine:

Transmission:

from

to

from

to

Cadillac

Escalade Models

2015

2019

L83, L86, LV1, LV3 (4.3L, 5.3L, 6.2L)

All

Chevrolet

Silverado

2014

2018

Silverado LD

2019

2019

Suburban

2015

2019

Tahoe

GMC

Sierra

2014

2018

Sierra Limited

2019

2019

GMC

Yukon Models

2015

2019

Some customers may comment about a rough idle and/or vibration at idle in Drive.

This condition may be most noticeable following extended driving, after hard acceleration, while idling at a stop in Drive.

May feel like a lopey or lumpy idle, or may be described as a low idle.

This condition will not be present in Park or Neutral. (There have been a few cases for rough idle in Reverse.)

Note: There will not be any DTCs with this concern.

If the rough idle / vibration concern frequency is E1.5 in the horizontal / lateral direction with Pico sensor mounted in seat track as indicated below – continue with steps to install updated design engine mounts and settle both engine and trans mounts to reduce amplitude (mg) / eliminate ground out within the engine mounts for vehicles built prior to engine mount breakpoint. For vehicles built after breakpoint, follow Shimming Procedure for Engine Mount Vibration/Grounding after Mount Replacement.

SO THE DEALERSHIP NEEDS TO EITHER PUT SHIMS OR REPLACE THE ENGINE MOUNTS

Thanks for all this info. Went to dealer with information. They confirmed motor mounts are the problem. Changed them and idle is smooth. The dealer claims this was the first they did. Can’t figure out how no one else notices.

jay webb · September 15, 2019

8 minutes ago, Bob2C said:

Thanks for all this info. Went to dealer with information. They confirmed motor mounts are the problem. Changed them and idle is smooth. The dealer claims this was the first they did. Can’t figure out how no one else notices.

lol we do mounts all the time. this is a common issue on these trucks due to the stiffer frame and body mounts.

dvzzz · October 14, 2019

I see that rough idles happens to other trucks with no codes, mine is like that. Two dealers said, your vehicle is perfect. However, a former GM lead mechanic here told me that if rough idle is irregular at the stop, but smoothes out with RPMs then this is an issue with compression most likely, very expensive to find the problem but he said he would do Leak Down Test. Dealers flat refuse to do that. Is Leak Down Test effective on the engine with 8,000 miles?