Broken Intake Valve from Valve Float 6.2L L92?

[Eryn]

Hi, has anyone else had this same problem, mine is an 07 Denali 6.2L and has 94000km on it. We were just getting up to speed on the highway and there was a loud ticking noise and a drop in power, then the computer started shutting stuff down and it died, I got it going and made it my friends shop, barely. So there was a P0305 Misfire Cyl #5, so after some diagnosing we finally found that the Intake Valve on #5 Cyl had broken off just below the Keepers. Luckily the Valve did not drop down and get caught but it was bouncing Up & Down(my ticking noise) and marked the Piston but it could have been catastrophic if the Valve had of exited the head or went through the Piston.
So we removed the Driver Side Head and took it to my Local Machine Shop and after tearing it down I was told that all of the Valve Seats had been pounded from Valve Float. So I just removed the Passenger Side Head and I am having all New GM Valves(I guess there are no aftermarket Valves for my L92) and we talked about doing a Spring Change but after finding out that the only Springs we could find were $700.00can(they are not Beehives but a traditional Double Spring) we decided to Shim the Factory Springs to get a little bit extra pressure out of them.
Has anyone out there had anything similar happen? My Denali has had very little added to it, a K&N Cold Air, Throttle Body Spacer and a Bully Dog Tuner(set on the 87 Octane setting). It has just over 94000km on it and I run MSD Wires and NGK Iridium Plugs. My problem here is that other then the odd hard run on the highway I drive it like I own it, I am very disappointed with my 6.2L at this point, I love the power but it should not be having these problems with so few KMs on it. Also my Denali does not have the Active Engine Management or the VVT, I have been told that an 07 should have the 4cyl shutoff but mine does not. Any one out there with any knowledge or anyone that knows of an ongoing problem let me know, Todd.

Sounds like im having the same problem you did a couple years ago. Haven't inspected the head yet but not looking forward to it either.

 

[Lsnoob13]

hello, i have similar issues. A friend had the truck when the issues initially started. She describes a ticking noise at idle as well as while in drive. she drove it like that for a while against my recommendation. She was on a road trip when loss of power and a cloud of smoke came from the exhaust. i have since bought the truck from her. the truck is an 07 yukon xl denali. L92 engine. code it threw when i first checked it was cylinder 8 misfire. so i got new plugs and wires. plugs on passenger side were soaked in fuel and real dark drivers side were dry and looked like normal wear. i rediagnosed it with my odll and it gave multiple cylinder misfire. i moved the truck to my home via trailer. hooked the obll up again after erasing all codes and it gave me cylinder 8 misfire. it has a rough idle smell of gas through exhaust and grayish smoke. i put a scope camera through the spark plug hole and pistons look dirty but are in tact. no debris on pistons. can you guys give me pointers.

 

[Hi-psi]

@Lsnoob13 - Just spit balling here, but I've seen where an injector (or more) could be leaking or stuck open and it's just pouring fuel to those cylinders. Pull the injectors and take them somewhere to get them cleaned/tested/flowed. If you can't, or don't want to throw money at something that might not be the issue, swap the left and right bank injectors with each other and see if the problem moves with it.

 

[swathdiver]

Can your scan tool see the fuel rail pressure and or test the injectors? Check for rapid pressure drop after turning it off. With the scan tool you can run a test on them too or just command them on and off and listen/watch the idle.

 

[Warriorpluto]

I would start with injectors like the others said. I just replaced all of mine. I had cylinder eight misfire and also has injector code. Since piston is good I would change the injector and see.

 

[Lsnoob13]

Im not to sure if my obll can do that i havent tried ill see if i can post a picture of it and see if you guys might be more knowledgeable than me about it. Ill see about the manual when i get back to the batcave. I will see if swapping injectors from banks will move it.....im always open to stuff that is free lol mine hasnt showed any injector codes but it never hurts to try

 

[Lsnoob13]

Ok so i finally got time to tinker with the truck. Battery dies to i had to jump it but once i got it started i read the codes and it didnt show any. I dont remember erasing them from last time but i guess thats due to the battery dieing. Anyway once i got it started o recorded a few clips to show you guys. Has a rough idle and smoke from the tailpipe. Looks whiteish-grey to me im not sure. Still throws cylinder 8 misfire. Im doing the injector bank swap as i write this but just stopped to throw this in here to give you guys a better idea of whats going on.

 

[Lsnoob13]

Well here it is.

 

[Lsnoob13]

Im taking pictures as i go through the process of swapping banks of injectors. Here are the injectors after i took them out. Top row is passenger side bottom is driver. They are in order as they came out so closest to the edge is ones that came out closest to firewall so top row far right is cylinder 8. They have carbon buildup so ill clean them with some carb cleaner before throwing them back in. Ive been debating about letting them sit in carb cleaner though, what do you think?

 

[Lsnoob13]

So i swapped the injecrors, cleared the codes and fired it up....still cylinder 8 misfire. So im guessing its a lifter or maybe head is cracked?