russian rocket Posted January 2, 2017 Report Share Posted January 2, 2017 hey guys i just wanted to pick your brains real quick. i really wanted another opinion before i tear the top half of this engine apart. i have a 2007 yukon denali xl, it has the l92 (vortec 6200) engine in it (basically an ls3) the vehicle currently has 180k miles on it and its been a great vehicle. Here is the problem though, for the past 10-15k miles, maybe more. there has been a distinct knocking noise coming from the engine. this noise has somewhat bewildered me. it really only happens when you are on the freeway for quite awhile and cruising with the rpms right around 18-1900 range. the sound is very distinct, sounds almost like a rod knock. the problem is, if you give it a little throttle, the noise speeds up and then goes away completely. its not there at idle or really anything below 1600 rpms. the vehicle runs great without any problems or hic ups. it also comes and goes on its own, you can be driving with the cruise control set and it will come and go. i can take long trips to visit my parents in michigan and never hear it once. lately though the sound has been coming around more often. so at this point i am kind of leaning towards it being a lifter that is on its way out and the reason the noise goes away with rpms is due to increased oil pressure. i have been mulling over the idea of pulling the engine and rebuilding it because it has horrendous piston slap on cold start (thanks gm), but if you guys also think its just a bad lifter, i might just do that for now. Quote Link to comment Share on other sites More sharing options...
cdk 4219 Posted January 2, 2017 Report Share Posted January 2, 2017 That sounds like lower end problems, have you tried a bit thicker oil 5w40 rotella or something like that. It may be a lifter, but those aren't knocks , usually taps. It could also be a flex plate loose or going bad, it can duplicate those sounds. It usually takes a lot of neglect or abuse to take that engine platform out that quickly. Quote Link to comment Share on other sites More sharing options...
russian rocket Posted January 2, 2017 Author Report Share Posted January 2, 2017 That sounds like lower end problems, have you tried a bit thicker oil 5w40 rotella or something like that. It may be a lifter, but those aren't knocks , usually taps. It could also be a flex plate loose or going bad, it can duplicate those sounds. It usually takes a lot of neglect or abuse to take that engine platform out that quickly. i have not tried thicker oil, its my wifes DD and she always takes it to oil change places to get the oil changed. the only reason i am still having a hard timing thinking its a rod bearing is because of how inconsistent the noise is. i can not replicate it if i try, it comes and goes on its own. also the engine shows good oil pressure on the factory gauge, have not had a chance to hook up my mechanical gauge. Quote Link to comment Share on other sites More sharing options...
Not Brian Posted January 2, 2017 Report Share Posted January 2, 2017 I wouldn't be surprised if it's a DoD issue. They're notorious for that. Quote Link to comment Share on other sites More sharing options...
russian rocket Posted January 2, 2017 Author Report Share Posted January 2, 2017 I wouldn't be surprised if it's a DoD issue. They're notorious for that. that would make things much easier, unfortunately this is not a DOD/AFM engine. The L99 was the engine that had the DOD/AFM system Quote Link to comment Share on other sites More sharing options...
Not Brian Posted January 2, 2017 Report Share Posted January 2, 2017 I got it confused with an L76 actually. The L99's didn't come out until 2010. Quote Link to comment Share on other sites More sharing options...
gillbot Posted January 2, 2017 Report Share Posted January 2, 2017 Try a thicker oil first. I would run a quart of 15-40 or 15-50 then top it off with 5-30 or 10-30 and see if that helps. Quote Link to comment Share on other sites More sharing options...
cdk 4219 Posted January 2, 2017 Report Share Posted January 2, 2017 It may be a wrist pin, not necessarily a rod issue. Lifter noise is half the speed of the crank and more of a click than a clunk like lower end noise. Wrist pin noise is in between the two, and can come and go depending on load and rpm. It could also be an exhaust leak that is mistaken for either noise. To many untrained ears, this sounds like bad lifters, and with the fact that these trucks have motor mounts that sag over time, leaving the 2.75" down pipe at a different angle than the exhaust flange. This in turn puts pressure on the back manifold bolts, and breaks them leaving an exhaust leak. If you are missing the rear exhaust manifold bolts, replace motor mounts and exhaust gaskets with bolts. Pull inspection cover and check flexplate for cracks, and try a thicker oil, synthetic diesel 5 w 40, or at least a thick additive to increase oil pressure to see if that fixes the problem. Quote Link to comment Share on other sites More sharing options...
AudiOn19s Posted January 2, 2017 Report Share Posted January 2, 2017 That sounds like lower end problems, have you tried a bit thicker oil 5w40 rotella or something like that. It may be a lifter, but those aren't knocks , usually taps. It could also be a flex plate loose or going bad, it can duplicate those sounds. It usually takes a lot of neglect or abuse to take that engine platform out that quickly. +1 on the flex plate. Take the inspection cover off the tranny and look really carefully at the flex plate for cracks. I went through something very similar for over 6 months trying to chase down a noise on my truck and it wasn't until the flex plate got really bad that I was finally able to isolate the issue. I swore the bottom end of my motor was coming apart. http://i136.photobucket.com/albums/q192/ZainoDetail/FCB34098-E837-471B-BC26-32B8E08840CB_zpscbqg80wq.jpg Quote Link to comment Share on other sites More sharing options...
russian rocket Posted January 2, 2017 Author Report Share Posted January 2, 2017 It may be a wrist pin, not necessarily a rod issue. Lifter noise is half the speed of the crank and more of a click than a clunk like lower end noise. Wrist pin noise is in between the two, and can come and go depending on load and rpm. It could also be an exhaust leak that is mistaken for either noise. To many untrained ears, this sounds like bad lifters, and with the fact that these trucks have motor mounts that sag over time, leaving the 2.75" down pipe at a different angle than the exhaust flange. This in turn puts pressure on the back manifold bolts, and breaks them leaving an exhaust leak. If you are missing the rear exhaust manifold bolts, replace motor mounts and exhaust gaskets with bolts. Pull inspection cover and check flexplate for cracks, and try a thicker oil, synthetic diesel 5 w 40, or at least a thick additive to increase oil pressure to see if that fixes the problem. i would say this noise is probably close to half the speed of the rpms if not less, it definitely does not sound like its knocking 1800 times a minute. ill take it for a spirited drive on wednesday and see if the noise comes and ill try to get a video of it. ill also check out everything you told me to, thank you Quote Link to comment Share on other sites More sharing options...
russian rocket Posted January 2, 2017 Author Report Share Posted January 2, 2017 +1 on the flex plate. Take the inspection cover off the tranny and look really carefully at the flex plate for cracks. I went through something very similar for over 6 months trying to chase down a noise on my truck and it wasn't until the flex plate got really bad that I was finally able to isolate the issue. I swore the bottom end of my motor was coming apart. http://i136.photobucket.com/albums/q192/ZainoDetail/FCB34098-E837-471B-BC26-32B8E08840CB_zpscbqg80wq.jpg yikes, thats bad lol if i remember correctly, my yukon doesnt have an inspection cover, ill have to drop the starter to take a look Quote Link to comment Share on other sites More sharing options...
caseyctsv Posted January 2, 2017 Report Share Posted January 2, 2017 Check the header bolts - I thought I had a lifter going but ended up being an exhaust leak. The heads of the header bolts pop off - very common. Quote Link to comment Share on other sites More sharing options...
Cordell Posted January 2, 2017 Report Share Posted January 2, 2017 Lots of good info in this thread. Just because it comes and goes doesn't mean that it's not just something broken, I've seen stranger things. Just don't rule anything out without inspecting. Valve covers are easy to pull off and check pushrods, springs, and rockers. I wouldn't rule out a flexplate but it's pretty hard to inspect, there's a small inspection cover on the bellhousing but even if you pull the starter you won't be able to see the center where it might crack, you would think that would be more consistent but like I said stranger things have happened. Quote Link to comment Share on other sites More sharing options...
russian rocket Posted January 2, 2017 Author Report Share Posted January 2, 2017 Lots of good info in this thread. Just because it comes and goes doesn't mean that it's not just something broken, I've seen stranger things. Just don't rule anything out without inspecting. Valve covers are easy to pull off and check pushrods, springs, and rockers. I wouldn't rule out a flexplate but it's pretty hard to inspect, there's a small inspection cover on the bellhousing but even if you pull the starter you won't be able to see the center where it might crack, you would think that would be more consistent but like I said stranger things have happened. definitely agree, there are a bunch of good suggestions in here that i am going to follow up on. will start with the easiest...header bolts lol my wife bought me an inspection camera a few years back, i guess ill finally be able to put it to some good use Quote Link to comment Share on other sites More sharing options...
evil8 Posted January 2, 2017 Report Share Posted January 2, 2017 Just did a flexplate on my 2500 Suburban. You can usually investigate those by varying the load with the transmission. You can hear a change by shifting into neutral drive or reverse and see if the knock changes. The 4L60e thru 4L70e have the 2 inch inspection plug, the 4L80E has a removable 6 bolt inspection cover. The bulk of the damaged flexplates on LS drive trains crack around the 6 bolts that the plate attachs to the crank. Quote Link to comment Share on other sites More sharing options...
AudiOn19s Posted January 4, 2017 Report Share Posted January 4, 2017 yikes, thats bad lol if i remember correctly, my yukon doesnt have an inspection cover, ill have to drop the starter to take a look My truck only had the 2 small inspection holes not a full cover either which is why it too me so long to finally find the issue with my flex plate. If you have that inspection camera it might be the ticket. I pulled my starter at one point too and still wasn't certain until it really broke free...while I was 500 miles from home....pulling the track car on a trailer. :-( Quote Link to comment Share on other sites More sharing options...
evil8 Posted January 5, 2017 Report Share Posted January 5, 2017 What was the tab for that? Quote Link to comment Share on other sites More sharing options...
TheManInDboX Posted January 30, 2017 Report Share Posted January 30, 2017 hey guys i just wanted to pick your brains real quick. i really wanted another opinion before i tear the top half of this engine apart. i have a 2007 yukon denali xl, it has the l92 (vortec 6200) engine in it (basically an ls3) the vehicle currently has 180k miles on it and its been a great vehicle. Here is the problem though, for the past 10-15k miles, maybe more. there has been a distinct knocking noise coming from the engine. this noise has somewhat bewildered me. it really only happens when you are on the freeway for quite awhile and cruising with the rpms right around 18-1900 range. the sound is very distinct, sounds almost like a rod knock. the problem is, if you give it a little throttle, the noise speeds up and then goes away completely. its not there at idle or really anything below 1600 rpms. the vehicle runs great without any problems or hic ups. it also comes and goes on its own, you can be driving with the cruise control set and it will come and go. i can take long trips to visit my parents in michigan and never hear it once. lately though the sound has been coming around more often. so at this point i am kind of leaning towards it being a lifter that is on its way out and the reason the noise goes away with rpms is due to increased oil pressure. i have been mulling over the idea of pulling the engine and rebuilding it because it has horrendous piston slap on cold start (thanks gm), but if you guys also think its just a bad lifter, i might just do that for now. I know you have likely already pulled the motor.. But.. Are you sure it's not a rattle? Like a flex fan issue hitting a housing, which was common on these, hitting the shroud or a heat shield hitting on something metal under the truck, also common.. Or the very well known Flexplate issues with the 6.2? I would start it, and if you know someone with a lift, look under the truck while it's running.. I would imagine if it were a Knock as you describe, 15K miles would have either made it much worse, or locked it up.. Quote Link to comment Share on other sites More sharing options...
russian rocket Posted January 30, 2017 Author Report Share Posted January 30, 2017 I know you have likely already pulled the motor.. But.. Are you sure it's not a rattle? Like a flex fan issue hitting a housing, which was common on these, hitting the shroud or a heat shield hitting on something metal under the truck, also common.. Or the very well known Flexplate issues with the 6.2? I would start it, and if you know someone with a lift, look under the truck while it's running.. I would imagine if it were a Knock as you describe, 15K miles would have either made it much worse, or locked it up.. i have not found the motivation to pull the engine yet and with me recently fracturing my elbow, itll be awhile longer. the noise is very inconsistent but i guess it could still be possible that something is loose. my main concern is that it is a very distinct knocking noise. one that sounds nearly identical to a rod knock. in the end regardless of what the problem is, i will more than likely pull the engine and rebuild it, the piston slap is driving me crazy and i dont think i cant handle listening to it for much longer. Quote Link to comment Share on other sites More sharing options...
russian rocket Posted February 26, 2017 Author Report Share Posted February 26, 2017 It may be a wrist pin, not necessarily a rod issue. Lifter noise is half the speed of the crank and more of a click than a clunk like lower end noise. Wrist pin noise is in between the two, and can come and go depending on load and rpm. It could also be an exhaust leak that is mistaken for either noise. To many untrained ears, this sounds like bad lifters, and with the fact that these trucks have motor mounts that sag over time, leaving the 2.75" down pipe at a different angle than the exhaust flange. This in turn puts pressure on the back manifold bolts, and breaks them leaving an exhaust leak. If you are missing the rear exhaust manifold bolts, replace motor mounts and exhaust gaskets with bolts. Pull inspection cover and check flexplate for cracks, and try a thicker oil, synthetic diesel 5 w 40, or at least a thick additive to increase oil pressure to see if that fixes the problem. well you might be onto something here, over the past couple weeks the noise has increased in how often it shows up and how loud it is. so i finally took a look and found the drivers side rear two exhaust manifold bolts were missing. took out my inspection camera and see the the furthest one back might have a little meat left on it to grip with some vice grips but the other one next to it is broken off flush. also i decided to test the motor mounts and the driver side is in fact broken. the passenger side still seems good. so looks like im going to tackle these two issues first, fingers crossed that this fixes the problem and holds me over a little longer before i eventually pull the engine or trade it in lol Quote Link to comment Share on other sites More sharing options...
caseyctsv Posted February 27, 2017 Report Share Posted February 27, 2017 Check the header bolts - I thought I had a lifter going but ended up being an exhaust leak. The heads of the header bolts pop off - very common. You mean this guy might have had some good advice for once? Quote Link to comment Share on other sites More sharing options...
Geeesammy Posted February 27, 2017 Report Share Posted February 27, 2017 Those motor mounts are joyous to do at home. Quote Link to comment Share on other sites More sharing options...
zeitgeist57 Posted February 27, 2017 Report Share Posted February 27, 2017 You mean this guy might have had some good advice for once? Congratulations, Casey! Quote Link to comment Share on other sites More sharing options...
Cordell Posted February 27, 2017 Report Share Posted February 27, 2017 You mean this guy might have had some good advice for once? You know how many people don't listen to me, and I'm a GM certified tech? This is why I don't even bother much anymore, besides trying to be nice typically turns into getting taken advantage of. You and Doc are but a few who never tried to abuse my kindness, you'll never know how much I appreciate that. Quote Link to comment Share on other sites More sharing options...
caseyctsv Posted February 27, 2017 Report Share Posted February 27, 2017 Congratulations, Casey! When victories seldom come you should enjoy them when they venture your way Quote Link to comment Share on other sites More sharing options...
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