Revisit 2015 Silverado Sluggish, Rough Idle, Uneven Fuel Pressure

[John Grie]

I've searched this forum for a while and found similar symptoms but I could never find where anyone got any resolution.  I have a used 2015 Silverado Z71 4x4 with the 5.3l V8.  I bought it 4 months ago with 56k miles on it and now it has 62k.  A few months ago I started to notice that the truck was sluggish when going about 20mph and slowly accelerating.  I really had to step on the gas to get it to drop down a gear and pull out of the slump.  Then a week ago my truck started to idle roughly that felt like a misfire.  There was no CEL and gas mileage seemed to remain the same.  The engine shakes enough to make the antenna whip and you can see drinks in the center console rock back and forth.  

 

I brought into my dealership and they verified the shaking and checked in in P, D, N and R.  They diagnosed the issue with faulty motor mounts even though I said it is sluggish and missing.  Two days later they said to come pick it up and right when I got into the truck I could tell it wasn't fixed.  I had the service advisor come out and he profusely apologized.  A manager came out and verified that it wasn't fixed and ripped the advisor for not verifying the work.  They kept it another day and said they couldn't figure it out since there was no CEL but said the fuel pressure was significantly uneven between the left and right side of the engine.  They let me take it home over the weekend and made an appointment for me to bring it back later in the week and I would get a loaner vehicle.  He said they will be speaking with gm technicians to figure out what it could be.  

 

What was the resolution if any?

 

Thanks.

[tbarn]

There is only 1 fuel pressure sensor on the engine (high pressure). No left or right bank . Lean codes? Don't know they came to that conclusion, but it is a leap to say " fuel pressure was significantly uneven between the left and right side of the engine ".

[John Grie]

I wish I had a better explanation from what they told me.  I know they said that there was a significant difference in the fuel pressure but they didn't tell me any codes because they said they couldn't pull any codes.  It seems like they have no idea what they are doing unless the computer throws a code at them.  

[tbarn]

I would find another dealer. This one seems clueless.

[Canoepaddler]

one of the fuel pumps probably not up to snuff. I'd bet low pressure is starving the high pressure side a bit. But the low pressure pump could be trying to makeup for ailing high pressure pump. Hope it gets taken care of for you.

[John Grie]

So the dealership has had my truck since 9/6 and they seem to not be any closer to fixing it.  The service advisor called me yesterday to say they are running a vibration test on it that tells them where the vibration is coming from.  He said they can determine if it is suspension, transmission, tires, engine or other body sources.  He said they pulled all the diagnostics and everything is within specs.  He said the next step is to have the regional GM tech advisor come to study it.  

 

In the meantime they gave me a 2018 Silverado LT as a loaner but I'm ready to have my Z71 back.

[John Grie]

Got my truck back last Thursday.  They finally narrowed it down to a cracked exhaust valve spring on the #6 cylinder.  Now it runs like a champ and its not sluggish around corners.