What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[RooTBeeRthe1st]

My resonator delete didn't make any difference that I could tell. depending on your muffler, you might not have any annoying noises in the cabin. Just a muscular growl when on the throttle.

With the full stock exhaust, deleting the resonator literally doesn't do anything in the vehicle as far as sound or anything.
Aftermarket mufflers however, it can make a huge difference.

 

[iamdub]

With the full stock exhaust, deleting the resonator literally doesn't do anything in the vehicle as far as sound or anything.
Aftermarket mufflers however, it can make a huge difference.

I see how this makes sense. The resonator "cleans up" specific frequencies left over after the stock muffler. So, it would be less effective being bombarded with louder and different frequencies being passed by an aftermarket muffler. I'd like to see comparison vids of a factory resonator temporarily clamped to the exit of an aftermarket exhaust system, before the tip is installed.

 

[George B]

What section in the tech2 do yall use to watch for knock and spark ret@rd?

Have some rattling getting on the highway but it comes and goes. I see no spark knock when looking at the ignition data in my log file.

Maybe its something else making noise. I have heard it before but it has been a while.

 

[Doubeleive]

What section in the tech2 do yall use to watch for knock and spark ret@rd?

Have some rattling getting on the highway but it comes and goes. I see no spark knock when looking at the ignition data in my log file.

Maybe its something else making noise. I have heard it before but it has been a while.

sometimes it's the exhaust pipe, there is a spot where it clamps together on the passenger side I think it's between the front and rear passenger seat, mine was rattling there under specific rpms tightening it up did not help so the muffler shop put a couple tiny tacks on it. That section is unbolted and removed to get the transmission out which is why they only put a couple tacks so it could be ground off if the trans has to come out.

otherwise all that kind of data should be in the engine live data I have only gone in there to see if I was getting any misfire, watch fuel trims and monitor oil temperature

 

[gooffeyguy]

Also check all your exhaust manifold bolts. It may just be a very slight, tiny leak happening under certain conditions

 

[George B]

sometimes it's the exhaust pipe, there is a spot where it clamps together on the passenger side I think it's between the front and rear passenger seat, mine was rattling there under specific rpms tightening it up did not help so the muffler shop put a couple tiny tacks on it. That section is unbolted and removed to get the transmission out which is why they only put a couple tacks so it could be ground off if the trans has to come out.

otherwise all that kind of data should be in the engine live data I have only gone in there to see if I was getting any misfire, watch fuel trims and monitor oil temperature

Also check all your exhaust manifold bolts. It may just be a very slight, tiny leak happening under certain conditions

Thanks guys. Same thoughts I had. I will check the bolts. I have all ARP bolts in the manifolds so that isn’t scary to me now.

 

[Sparksalot]

Drove it to a hot rod show. Won a toolbox and a SnapOn pie iron in the auction. Saw a few cool hot rods.

 

[RooTBeeRthe1st]

I see how this makes sense. The resonator "cleans up" specific frequencies left over after the stock muffler. So, it would be less effective being bombarded with louder and different frequencies being passed by an aftermarket muffler. I'd like to see comparison vids of a factory resonator temporarily clamped to the exit of an aftermarket exhaust system, before the tip is installed.

My 3.5" stock style catback.
A Walker School bus muffler and universal resonator.
Just the muffler, and then holding the resonator up to get a rough idea.

I have since welded the resonator on in front of the muffler because I hate seeing that big turd hanging out behind the back tire on the factory exhaust.


Been running this exhaust for just over a year now.

 

[RooTBeeRthe1st]

What section in the tech2 do yall use to watch for knock and spark ret@rd?

Have some rattling getting on the highway but it comes and goes. I see no spark knock when looking at the ignition data in my log file.

Maybe its something else making noise. I have heard it before but it has been a while.

Belt tentioner?

 

[George B]

Belt tentioner?

Hmm… it has about 30k on it.

 

[RooTBeeRthe1st]

Drove it to a hot rod show. Won a toolbox and a SnapOn pie iron in the auction. Saw a few cool hot rods.

View attachment 382945View attachment 382946View attachment 382947

My luv is a bit more rough than that. Lol

 

[iamdub]

Took it apart.


First look as soon as I removed the head:

The complete ring where just the carbon is knocked off shows that the valve was riding the piston for a little while. This must've been during that time when I was cruising, had just noticed it and was trying to determine if the odd vibes I was feeling were from the driveline or a loose wheel. It was the steady rhythmic pulse of a dead cylinder. Had I known, I would've shut it down that instant and all I would've needed was a new valve spring which would've been a 3 hour fix on the side of the road to get me back home with no damage at all. But, at some point, the valve and piston had a disagreement and while the piston was trying to buck the valve off it's head, it bítch slapped it sideways, leading to the hoof marks in the piston:

Pulled a valve from a junk 706 head for comparison:

The head looks fine. It looks like it did little more than just knocking the carbon off. I don't know how it survived, but the guide looks and feels fine, too:

I buffed the carbon off the piston and smoothed the hoof marks to eliminate sharp edges that would lead to hot spots. The light reflecting makes them look more severe than they really are:

I pulled the lifters from that cylinder and they look fine. Plan of action is to clean up and install that salvaged valve, replace all 16 springs, reassemble and send it.

 

[Just Fishing]

My resonator delete didn't make any difference that I could tell. depending on your muffler, you might not have any annoying noises in the cabin. Just a muscular growl when on the throttle.

My wife says I'm the anoying noise in the cabin.

 

[gooffeyguy]

My wife says I'm the anoying noise in the cabin.

Funny, mine says the same thing to me

 

[Rocket Man]

Took it apart.


First look as soon as I removed the head:

View attachment 382966


The complete ring where just the carbon is knocked off shows that the valve was riding the piston for a little while. This must've been during that time when I was cruising, had just noticed it and was trying to determine if the odd vibes I was feeling were from the driveline or a loose wheel. It was the steady rhythmic pulse of a dead cylinder. Had I known, I would've shut it down that instant and all I would've needed was a new valve spring which would've been a 3 hour fix on the side of the road to get me back home with no damage at all. But, at some point, the valve and piston had a disagreement and while the piston was trying to buck the valve off it's head, it bítch slapped it sideways, leading to the hoof marks in the piston:

View attachment 382967


Pulled a valve from a junk 706 head for comparison:

View attachment 382968


The head looks fine. It looks like it did little more than just knocking the carbon off. I don't know how it survived, but the guide looks and feels fine, too:

View attachment 382969


I buffed the carbon off the piston and smoothed the hoof marks to eliminate sharp edges that would lead to hot spots. The light reflecting makes them look more severe than they really are:

View attachment 382970




I pulled the lifters from that cylinder and they look fine. Plan of action is to clean up and install that salvaged valve, replace all 16 springs, reassemble and send it.

Looks like you got real lucky.

 

[iamdub]

Looks like you got real lucky.

I'd say! I see a light at the end of the tunnel now, but I can't take any more steps toward it at the moment and it's making me anxious!

 

[Geotrash]

All this talk about broken valve springs had me thinking that I should replace the ones in my 2007 6.2 as I understand they had some bad ones that got into those years. But it seems that my engine may be considerably newer than the truck itself. A couple of years ago I pulled the drivers side valve cover to upgrade it to the newer version and found that it had already been done. The existing cover also had a date code of October, 2013. So today I though I'd look around for a few more date codes on other parts, and found one that said 10/30/13 on the front of the valley cover. Do any of y'all know if there are any other easily visible date codes I could check? Like maybe on the engine block itself?

 

[Rocket Man]

All this talk about broken valve springs had me thinking that I should replace the ones in my 2007 6.2 as I understand they had some bad ones that got into those years. But it seems that my engine may be considerably newer than the truck itself. A couple of years ago I pulled the drivers side valve cover to upgrade it to the newer version and found that it had already been done. The existing cover also had a date code of October, 2013. So today I though I'd look around for a few more date codes on other parts, and found one that said 10/30/13 on the front of the valley cover. Do any of y'all know if there are any other easily visible date codes I could check? Like maybe on the engine block itself?

View attachment 383026

You don’t have the history on your truck?

 

[Geotrash]

You don’t have the history on your truck?

Nope. I bought it used in 2018 with no records, from a local dealer in Colorado. All I knew is that it was an Arizona car and looked like it just rolled out of the showroom it was so clean. I do have the Carfax maintenance history which shows frequent routine maintenance, but lots of shops don't upload to Carfax so if it was a small shop who did the work, it may not show up on the report.

 

[SynnerD]

Got some lighting done this weekend and Flowmaster on it as well. Put the 22’s on too. All lights are oracle.