2015 GMC Sierra 96000mile misfire cylinder 6

[Xtreme Access]

I felt small vibration on the car every time I stop at stop light , I have read some forums and come up with adding fuel cleaners , I tried so but didn’t work , after 300 mile , I was driving and felt the car shaking bad And check engine light turned on And I can see blue smoke coming out of the tailpipe , I stopped and checked the code p0306 , any way drove the car home next morning I was about to Take it to a mechanic , drove it for 1 min and the the check engine light turned off and the car becomes normal , drove it for a couple of days , one time I hit the gas pedal hard and the misfire and the code come back with the the car shake and the blue smoke , I checked the ignition coil and the plug wires  ( swap 2 to 6 ) , with same issue , what could be the problem 

[CamGTP]

Did you pull the spark plug itself?

 

Blue smoke is oil, so the plug could be covered in oil because of the AFM/DoD system.

[tlaw91]

You either need an injector or a set of lifters and vlom. I’m leaning towards an injector.

-GM tech


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[Ozer]

I had this same thing happen, not sure what fixed it but im leaning towards the SEAFOAM fuel treatments i used. I narrowed it down to a clogged injector but a scan of the injectors and plugs/coils showed that everything was working as it should in real time. Use the seafoam treatment 2 bottles per tank, that may fix a clogged injector.

Knock on wood, i haven't had an issue after that, i still use it every few tanks. 

[davevinc1080]

I had the same issue, cylinder 7. I replaced the plug and wire in the affected cylinder. I have been running lucas injector cleaner with premium fuel and have not had the issue in 15,000K miles after it happened. Like other posters said likely an Injector, but hopefuly not the AFM DOD. 

 

After this happened I also bought a superchips 2845 tuner and deactivated the AFM. so far so good. Originally happened at 59K Miles and now at 79K

[Doublebase]

Had the same issue with a non AFM cylinder...think it was cylinder 5. Pulled the plug, swapped coils. Had misfires while going up hills occasionally. Ran some Techron through a couple times, seems fine now. It’s worth a try, otherwise probably needs an injector.

 

Edit— 2018 with 45,000 miles (at the time), now at 50,000. Still get a stutter occasionally on the highway while going up hills, sort of a stumble and loss of power. Check engine light hasn’t come back on and I can avoid it if I’m more into the throttle before approaching the hill. Not exactly what I was expecting out of a truck I bought new and is now not even two years old.

[Ozer]

I disabled AFM while ago, the truck just runs so much better, not worth keeping it on for those few mpg gains. With it on, my transmission was so confused, kept clunking.

In V8 mode it doesnt do any of that. Also run premium fuel for few tanks along with sea-foam or Techron cleaner. I used many many other brands and didn't see any difference with them.

One last thing, when you are running these cleaners dont be afraid to get on it and redline the truck few times to get those injectors firing nonstop. 

[mookdoc6]

I catch a lot of FLAK on here sometimes.  KEEP EM CLEAN LADIES!  KEEP THE GDI'S CLEAN!  You will not have problems.............

[diyer2]

IMO

Using Top fuel gas only instead of the cheapest gas around will help the fuel system stay clean.

Regular dose of fuel system cleaners also.

Some of these miss- fire issues could be avoided.

 

[amxguy1970]

On 3/21/2020 at 5:03 PM, CamGTP said:

Did you pull the spark plug itself?

 

Blue smoke is oil, so the plug could be covered in oil because of the AFM/DoD system.

 That didn't take long for the AFM haters to throw their hat in the ring, must be the AFM! Power seat failure, AFM! Tire losing air, AFM! Lots of flack for something that causes less issues than other parts on the truck.

 

If we wait a little longer the BFG crowd, Bilstein shock guys and amsoil fan boys will be in here too...

 

96k, throw some new plugs in there and run some good fuel system cleaner and top tier fuel. You already eliminated the wires and coil by swapping them.

 

Tyler

[Xtreme Access]

Hello guys thanks for your help , I took it to a local mechanic , after 24hours , I received a call from him he said the fuel injector on cylinder 6 is bad , he’s charging me about $700 to replace it , but he keeps pushing me to replace all of them , and to replace them all will cost $1900,
I end up changing on the bad injector I have never owned a pick up truck but this one is pushing away from pickups , 

any way my car still at the shop hopefully I can Get it today , 

also he told me there is a chance that it will misfire on other cylinders . 

 

[Doublebase]

18 hours ago, Xtreme Access said:

Hello guys thanks for your help , I took it to a local mechanic , after 24hours , I received a call from him he said the fuel injector on cylinder 6 is bad , he’s charging me about $700 to replace it , but he keeps pushing me to replace all of them , and to replace them all will cost $1900,
I end up changing on the bad injector I have never owned a pick up truck but this one is pushing away from pickups , 

any way my car still at the shop hopefully I can Get it today , 

also he told me there is a chance that it will misfire on other cylinders . 

 

What year and how many miles?

 

Edit — Didn’t realize you were the OP. You already gave the year and miles.

 

So it was the injector? Good to know. Price seems high for an independent shop. So you just changed one? I guess I can’t blame you, it’d cost you another grand for the rest.

[Xtreme Access]

On 3/21/2020 at 1:14 PM, Xtreme Access said:

I felt small vibration on the car every time I stop at stop light , I have read some forums and come up with adding fuel cleaners , I tried so but didn’t work , after 300 mile , I was driving and felt the car shaking bad And check engine light turned on And I can see blue smoke coming out of the tailpipe , I stopped and checked the code p0306 , any way drove the car home next morning I was about to Take it to a mechanic , drove it for 1 min and the the check engine light turned off and the car becomes normal , drove it for a couple of days , one time I hit the gas pedal hard and the misfire and the code come back with the the car shake and the blue smoke , I checked the ignition coil and the plug wires  ( swap 2 to 6 ) , with same issue , what could be the problem 

I’m the original poster for this topic here is the out come 

I took it to a mechanic and he told me it was fuel injector is bad on the cylinder 6 , he was trying to push me to change all the injectors for $1900 but I asked him to replace only the bad injector 

he was not happy for some reason , any way he kept the car for almost a week and when I called him today he’s said that I need to rebuilt the engine , I was like wtf, he said he changed the injector and still misfiring , I asked him if the engine pass the compression test he said yes ( dry and wet ) and he mentioned that a piston or cylinder ring is bad , he didn’t charge me anything , so now Im confused , the car is smoking a lot from the exhaust and the car shakes  ,  how can I make sure my engine is not bad ? The car was driving fine until o hit the gas hard and that’s it