2015 GMC will not run correctly after replacing coils and PCV valve

[mamarinelli]

Hi all I am at a loss with whats going on and could use some help.

 

After dealing with sputtering under load I finally went ahead and replaced all 8 coils with new NGK coils, new GM wires & Boshe plugs. Also replaced my PCV valve while I was in there because I cracked it when doing lifters a couple weeks ago. 

 

Started truck up after doing this work and the truck ran perfect. My issues were fixed.

 

Brought it home to change out my wheels and reinstall passenger side fender liner and now when I start the truck back up it will idle up and down between 350-1000 rpm then it will eventually die. I went back and checked all the connections, cleaned the MAF, Sprayed MAF cleaner while running to check for a vacuum leak. I was not able to find anything wrong. I cannot understand how I parked it running perfectly and now I cant even drive it.

 

Any help is much apricated 

 

EDIT - When I rev the motor it runs very well I do not feel any miss fires and the motor is not throwing any codes

Edited December 31, 2023 by mamarinelli

[BO TIE 1]

Did you clean the throttle body? Is it throwing any codes?

[mamarinelli]

Just now, BO TIE 1 said:

Did you clean the throttle body? Is it throwing any codes?

I quickly sprayed MAF cleaner in around the throttle body when I had intake off. No changes.

 

No codes unfortunately. 

[diyer2]

I would have used OEM coils and plugs.

[customboss]

MAF issue. Not bad enough for ECM mil to set. 

[Black02Silverado]

On 12/31/2023 at 4:53 PM, mamarinelli said:

Hi all I am at a loss with whats going on and could use some help.

 

After dealing with sputtering under load I finally went ahead and replaced all 8 coils with new NGK coils, new GM wires & Boshe plugs. Also replaced my PCV valve while I was in there because I cracked it when doing lifters a couple weeks ago. 

 

Started truck up after doing this work and the truck ran perfect. My issues were fixed.

 

Brought it home to change out my wheels and reinstall passenger side fender liner and now when I start the truck back up it will idle up and down between 350-1000 rpm then it will eventually die. I went back and checked all the connections, cleaned the MAF, Sprayed MAF cleaner while running to check for a vacuum leak. I was not able to find anything wrong. I cannot understand how I parked it running perfectly and now I cant even drive it.

 

Any help is much apricated 

 

EDIT - When I rev the motor it runs very well I do not feel any miss fires and the motor is not throwing any codes

It has been my understanding that going with anything other than AC Delco or NGK plugs can cause all kinds of issues.  I've seen many posts where someone tried a different brand, only to go back to AC Delco or NGK.  I always just stick with them.  Rock Auto sometimes runs specials on plugs. 

Edited January 2 by Black02Silverado

[mamarinelli]

1 hour ago, Black02Silverado said:

It has been my understanding that going with anything other than AC Delco or NGK plugs can cause all kinds of issues.  I've seen many posts where someone tried a different brand, only to go back to AC Delco or NGK.  I always just stick with them.  Rock Auto sometimes runs specials on plugs. 

That seems like it could be my issue then. what kind of issues are we talking about with the other brands? I just got back from driving the truck and it is spark knocking, and feels like its down on half of its power but no CEL and I dont hear or feel a misfire. Surprising a different brand of plugs could cause that?

[Black02Silverado]

1 hour ago, mamarinelli said:

That seems like it could be my issue then. what kind of issues are we talking about with the other brands? I just got back from driving the truck and it is spark knocking, and feels like its down on half of its power but no CEL and I dont hear or feel a misfire. Surprising a different brand of plugs could cause that?

From what I have read, individuals that used other manufacture plugs had the same issues you are having.  The switch out to AC Delco or NGK and back to normal.

[mikeyk101]

Just to add, counterfeit plugs have been flooding the market including with NGK. With counterfeit plugs, you will probably experience all kinds of engine problems including knocking, misfires, etc... If you switch out and go with NGK, check them carefully to make sure they are genuine. Wouldn't be a bad idea to also check if you get AC Delco either. 

 

I agree with @Black02Silverado as far as using OEM plugs as kind of an insurance policy. There are certain parts on these that the OEM choice just works out better than aftermarket.