Jump to content

2015 diagnostic mystery

Potius
 Share

Recommended Posts

Potius Enthusiast

Potius

Posted
Posted

Hello everyone so I’m praying someone has some advice for me. So I have a 2015 Silverado LT 1500 5.3L. About a month ago started running really rough down shifting rough and MIL is on. Scanned it and got P0308, P219B, and P050D. Checked live misfire data on scanner and cyl 8 had over 25k misfires. Next step I took was swapped spark plug, coil and wire from 8 to 4 cleared codes and started her up. No difference and misfire didn’t move cylinders. Used scanner to perform an injector balance test and both fuel rails have good pressure and all injectors tested within acceptable variance. Next pulled valve cover off and made sure all rockers were moving and rocking and they all looked great and in sync so ruled out stuck lifter. Did a compression test and compression is there at 150. So today cleared codes(due to coil pack change etc had some stored) and started it up. Now only codes I have are P0300 and U0401:00. Cylinder 8 is misfiring a lot and cylinder 7 seems to be missing more and more. Just for sh*** and giggles I plugged in the range afm disabler from my Tahoe and the truck seems to have smoothed out a lot and it’s barely rough but drives weird so I unplugged it after checking. So long story short I am completely stumped as to what could be causing my issues and any advice or help would be greatly appreciated.

rav3 Senior Enthusiast

rav3

Posted
Posted

How many miles?  Any modifications? Any tune ups or engine maintenance? 

Potius Enthusiast

Potius

Posted
  • Author
Posted

190k miles with no mods. Owned it since 105k maintained since then meticulously. No recent tune ups in last 30k other than fluid changes. Oh I did put a Rough Country cold air intake on it. As to the thread going to start reading it now and thank you for the link

Potius Enthusiast

Potius

Posted
  • Author
Posted

Thank you for that link asilverblazer. Definitely helped me zero down some things. So went back to testing concentrating on the fuel aspect. My pressures seemed within range 45-60psi low side and around 700’s high side at idle. Did the injector balance test/correction and I believe all injectors tested within acceptable variance. I attached the injector balance numbers. Here’s the thing though when doing the test there was a noticeable drop in rpm when I did each injector which is suppose to happen. However when I did injector 7 the feeling wasn’t as strong and when I did injector 8 you barely felt any hiccup at all. Injector 8 is the one with 45k misfires and injector 7 has 950.

Now with me ruling out most everything else and not having any lifter noise compression or spark issue etc would it be a safe bet to buy the 2 injectors for 7 and 8 and pick up a new hpfp. I figure it needs the injectors and with almost having 200k the hpfp should be around end of life so would be preventative if nothing else.

  • Like 1
asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted

A couple things...

1. At the most recent oil change did the old oil smell of gasoline? Sometimes the high pressure pump leaks to the crankcase. I don't recall specs for fuel rail pressure but 700 seems low.

2. I would pursue injectors or fuel pump separately. You've done the injector balance test and the results do not indicate an injector issue. You can run the test as many times as needed to confirm that result. If you choose to replace any injectors do so one at a time with a genuine GM part. I would try the high pressure fuel pump first if the pressure is indeed low. I would not replace the pump and injectors at the same time, too many variables start getting introduced. 

Potius Enthusiast

Potius

Posted
  • Author
Posted

Due to the fuel lines being 1 time use I’m going to do the 1 injector on cylinder 8 due to getting almost no change in rpm’s during injector test and the fuel pump. Wish me luck parts should be here in a few days

Potius Enthusiast

Potius

Posted
  • Author
Posted

On a side note rock auto tells me the correct injectors are the nominal flow part # 12710481. It’s the only gm genuine injector listed so I assume it’s right lol

asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted (edited)

Proceed with caution, there are counterfeit parts... the new one may end up being worse than the old one. 

 

I'm not being critical of your course of action, just warning you not to assume that putting a new injector in (or any part for that matter) rules it out as the culprit of the problem.

 

Be careful with the intake gaskets too. They are supposed to be replaced when you pull the manifold.

Edited by asilverblazer
  • 2 months later...
Potius Enthusiast

Potius

Posted
  • Author
Posted

Ok sorry for the time since last update. Finally got parts/time so went to remove cylinder 8 injector and course rail was stuck so bent that coming out. Ended up just putting a new passenger side fuel rail and 4 new injectors in it. Changed intake gaskets just to be sure and put everything back together. Double checked everything and started her back up. Not a single change. Everything is exactly as it was before with cylinder 8 misfiring. At this point I’m about to change the HPFP mainly due to being stumped what else it could. A quick recap:

spark plugs checked and verified there is spark

coil packs checked/ moved with no change

spark plug wires checked an spark verified

compression test good on all cylinders

took valve cover off and all rockers good and doesn’t look like stuck lifter at all

checked for vacuum leaks and smoke tested 

 

Honestly if it’s not the HPFP then it must be electrical and I’m way out of my league 

 

asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted (edited)
21 hours ago, Potius said:

Ok sorry for the time since last update. Finally got parts/time so went to remove cylinder 8 injector and course rail was stuck so bent that coming out. Ended up just putting a new passenger side fuel rail and 4 new injectors in it. Changed intake gaskets just to be sure and put everything back together. Double checked everything and started her back up. Not a single change. Everything is exactly as it was before with cylinder 8 misfiring. At this point I’m about to change the HPFP mainly due to being stumped what else it could. A quick recap:

spark plugs checked and verified there is spark

coil packs checked/ moved with no change

spark plug wires checked an spark verified

compression test good on all cylinders

took valve cover off and all rockers good and doesn’t look like stuck lifter at all

checked for vacuum leaks and smoke tested 

 

Honestly if it’s not the HPFP then it must be electrical and I’m way out of my league 

 

I don't think a HPFP would only cause problems on a specific cylinder. 

 

Did you swap plug and plug wires from a good non missing cylinder?

 

Good ignition, good fuel... inspect everything from the cam shaft to the valves.

 

Take a look here:

 

Edited by asilverblazer
Potius Enthusiast

Potius

Posted
  • Author
Posted

I swapped plugs and wires with 2 other cylinders to be sure and no change as well as checked for spark and it has it. I’ve literally checked everything 

silveradosid Senior Enthusiast

silveradosid

Posted
Posted

i would hook a vacuum gauge to the intake manifold, should be 18 to 20 inch vacuum. the needle on the gauge should stay still. if the gauge is fluctuating then you have a valve problem. does it take more cranking on cyl 8 to get good compression.

Potius Enthusiast

Potius

Posted
  • Author
Posted

Where do you connect a vacuum gauge on this engine? It doesn’t seem to have vacuum lines and I thought the brake booster line didn’t work for a gauge cause it goes directly to the vacuum pump and not into the engine

Potius Enthusiast

Potius

Posted
  • Author
Posted

Ok so I decided to not buy another part until I actually found something damaged or wrong. Unfortunately that only left valves lifter and cams to check. So had a fun day today in the cold(northern Maine here) and here is what I found so far:

valve pic (cylinder 8 is the black valves)

IMG_0523.jpeg

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.

  • Forum Statistics

    250.4k
    Total Topics
    2.7m
    Total Posts

  • Member Statistics

    342,760
    Total Members
    8,960
    Most Online
    MASONV88888888
    Newest Member
    MASONV88888888
    Joined

  • Who's Online   1 Member, 0 Anonymous, 1,541 Guests (See full list)

  • Latest Articles

  • Posts

    • MASONV88888888
      Another 6.2L engine failure!

      By MASONV88888888 · Posted

      My 2025 Silverado 1500 had to receive a brand-new engine (long block) under warranty last month at only around 16,500 miles. Before the replacement, the truck repeatedly displayed "Engine Oil Level Low" warnings, even though the Oil Life Monitor still showed around 50% remaining after about 6,000 miles since my last oil change. After seeing the warning several times, I checked the dipstick with the engine cold, and the oil level was completely normal. The next day, the message escalated to "Add Engine Oil." At first, I assumed it was just a faulty oil level sensor, so I brought the truck to the dealership. After inspecting the engine, they found internal cylinder wall scoring and ultimately replaced the entire long block under warranty. Before this happened, I was planning to install a 4-inch lift and suspension upgrade on my truck. After needing a new engine at just 16,500 miles, I honestly don't see the point anymore. I also contacted GM to ask whether my vehicle qualified for a buyback, but I was informed that it does not at this time. Anyway, this experience has left me with serious concerns about the long-term reliability of this engine. I sincerely hope NHTSA expands the current investigation or recall to include 2025 model and performs a thorough inspection of affected vehicles. My biggest concern is that these engines may fail shortly after the powertrain warranty expires. If GM truly stands behind this engine, then at the very least, please consider extending the powertrain warranty to 10 years for affected owners. That would go a long way toward restoring customer confidence.
    • Grumpy Bear
      OCI, not when but why?

      By Grumpy Bear · Posted

      Without exception but then I'm the odd duck, right? I know what goes into that test, how it is calculated and thus how to beat it. But EPA values are often not beaten by the general public and the government has in past years adjusted the means and methods to come to those values to more closely approximate "Joe Average".    The only real trick to beating that EPA average is don't drive like "Joe Average".    It's the same method you used to profit from "Economic Migration" and in doing so beat the 'stats'. But you, like me, are not "Joe Average".     The thing you don't seem to grasp is this "Purchasing Power Index" isn't forward looking. It doesn't predict what it going to be but looks backward and states what it was. They are not telling us what the THINK, they are telling us what they MEASURED. Example:    Wife says "I'm going to lose 40 pounds by Christmas". May she does, maybe she doesn't but the doctors office who weighed her when she made that statement and again at Christmas only REPORTS what the RESULT was. You and I can banter about what was possible and what aunt Tilly did till the cows come home but the result is the result. Arguing otherwise is.....irrational. That's all I'm saying. This isn't about:      What you are calling a 'Statistic' is a RESULT not a CALCUATION and as a result the RULE. Like gravity as a rule, it can not be broken. 
    • MASONV88888888
      Rattle in the rear!

      By MASONV88888888 · Posted

      Just wanted to say thank you for posting this. Years later, your thread is still helping Silverado owners.   I bought my 2025 Silverado 1500 in January 2025, and I've had what feels like the exact same rattle since day one. After reading your findings, I believe my truck has the same issue with the cable carrier contacting the rear sliding window. To be honest, I had pretty much given up on pursuing the issue. It wasn't until I recently drove another brand's pickup that I realized just how quiet their cabin was—and how noisy mine has been all along. On my truck, the rattle happens on almost any paved road, gets even worse on rougher pavement, and I can even hear it during braking and acceleration.   I actually referenced your thread when submitting my case to GM, hoping they'll recognize this as a recurring issue instead of treating it as an isolated incident. The reason I reached out to GM first is because my dealership told me they would need to keep the truck for at least two days just to diagnose the problem. I was concerned that even after two days, they still might not be able to identify the source of the rattle before giving the truck back to me. I had also asked a few dealerships about this issue during previous service visits, but none of them seemed to know what was causing it or had a solution. That's why I decided to contact GM directly first, hoping they might already have an official repair procedure or guidance for this issue.   I also hope GM eventually comes up with an official fix for this problem. I have a feeling there are many Silverado owners experiencing the same rattle, but most either choose to live with it or simply don't know what the cause is.   Really appreciate you taking the time to document your diagnosis. Your post is still making a difference years later.
    • Buckwild27
      Gas Prices

      By Buckwild27 · Posted

      I have 2 choices. 
    • Grumpy Bear
      Gas Prices

      By Grumpy Bear · Posted

      Do you have access to BP fuels? Some stations have Silver 91 E-0 priced the same as their 93 E-10.  There is a local Marathon with 90 alky free for $6 a gallon but I go down the road to BP for $5-ish. They also have a 100 E-0 but that stuff is $10 a pop. 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...