Random Misfire after Overheating 2013Yukon Denali 6.2L

[13UpInSmoke]

Ok so about 2-3 months ago I ended up overheating my truck while driving around town. Cant believe I didnt see it but is what it is. Previously I have swapped the radiator, upper & lower hoses, heater hoses & bulk head connections, water pump, thermostat & full flush. When I did all of that I had one of the heater hose replacements with the Dorman metal/aluminum connections didn't seat correctly & wouldn't hold the seal so I swapped that one hose back to the stock with the intention of going back & fixing it later. Course that didn't happen & its what failed completely. So I get the truck back to the house limped it home with gallons of water & some hose crimps. Once I got the hose fixed correctly, refilled the cooling system & cleared the codes the truck will run fine but then every once in a while I will get a P0300 random misfire. Sometimes the trac & stability go off as well, the truck will shudder & run kinda ruff for a minute & then it goes back to normal & the check engine light goes off. I have done the head gasket check with pump & fluid thing that goes on the resevoir. Ive also pulled the plugs & checked gaps & looking for any impacts on them & they all checked out. Along with doing a compression test. All cylinders between 200-212 psi. What am I missing? Bent valve or push rod maybe or something else?? I'm stumped. Truck has about 150K on it.

 

[Fless]

Use a scanner that can log individual cylinder misfires, and drive it around to see what goes on when the issue happens.

 

[j91z28d1]

is afm active? if so it possible with the over heat that the lifters aren't happy and one is sticky coming in and out of 4cyl?

 

[13UpInSmoke]

No its deactivated in the tune

 

[solli5pack]

Ok so about 2-3 months ago I ended up overheating my truck while driving around town. Cant believe I didnt see it but is what it is. Previously I have swapped the radiator, upper & lower hoses, heater hoses & bulk head connections, water pump, thermostat & full flush. When I did all of that I had one of the heater hose replacements with the Dorman metal/aluminum connections didn't seat correctly & wouldn't hold the seal so I swapped that one hose back to the stock with the intention of going back & fixing it later. Course that didn't happen & its what failed completely. So I get the truck back to the house limped it home with gallons of water & some hose crimps. Once I got the hose fixed correctly, refilled the cooling system & cleared the codes the truck will run fine but then every once in a while I will get a P0300 random misfire. Sometimes the trac & stability go off as well, the truck will shudder & run kinda ruff for a minute & then it goes back to normal & the check engine light goes off. I have done the head gasket check with pump & fluid thing that goes on the resevoir. Ive also pulled the plugs & checked gaps & looking for any impacts on them & they all checked out. Along with doing a compression test. All cylinders between 200-212 psi. What am I missing? Bent valve or push rod maybe or something else?? I'm stumped. Truck has about 150K on it.

Any smoke coming out of the tail pipe on first start up of the day?Is the coolant level dropping with no visible signs of a leak? Reason I ask is my wife overheated our Burb that eventually caused a head gasket failure that turned into a misfire on I believe was cyl 4. Coolant would leak slightly onto the plug overnight but would burn off when I started it in the a.m. I had the misfire code and the traction control lights and all that until the coolant would burn off. I did all the compression tests and coolant system test and everything came back fine. I guess because it was a slight leak. I ended up using the opportunity to do a DOD delete.

 

[swathdiver]

Ok so about 2-3 months ago I ended up overheating my truck while driving around town. Cant believe I didnt see it but is what it is. Previously I have swapped the radiator, upper & lower hoses, heater hoses & bulk head connections, water pump, thermostat & full flush. When I did all of that I had one of the heater hose replacements with the Dorman metal/aluminum connections didn't seat correctly & wouldn't hold the seal so I swapped that one hose back to the stock with the intention of going back & fixing it later. Course that didn't happen & its what failed completely. So I get the truck back to the house limped it home with gallons of water & some hose crimps. Once I got the hose fixed correctly, refilled the cooling system & cleared the codes the truck will run fine but then every once in a while I will get a P0300 random misfire. Sometimes the trac & stability go off as well, the truck will shudder & run kinda ruff for a minute & then it goes back to normal & the check engine light goes off. I have done the head gasket check with pump & fluid thing that goes on the resevoir. Ive also pulled the plugs & checked gaps & looking for any impacts on them & they all checked out. Along with doing a compression test. All cylinders between 200-212 psi. What am I missing? Bent valve or push rod maybe or something else?? I'm stumped. Truck has about 150K on it.

These Gen IV 6.2s are known for dropping a valve guide when they overheat. Usually cylinders 7 and 8.

I reckon the only way to check that is by camera.

 

[13UpInSmoke]

Any smoke coming out of the tail pipe on first start up of the day?Is the coolant level dropping with no visible signs of a leak? Reason I ask is my wife overheated our Burb that eventually caused a head gasket failure that turned into a misfire on I believe was cyl 4. Coolant would leak slightly onto the plug overnight but would burn off when I started it in the a.m. I had the misfire code and the traction control lights and all that until the coolant would burn off. I did all the compression tests and coolant system test and everything came back fine. I guess because it was a slight leak. I ended up using the opportunity to do a DOD delete.

No no smoke & the coolant is staying at the same level

 

[13UpInSmoke]

These Gen IV 6.2s are known for dropping a valve guide when they overheat. Usually cylinders 7 and 8.

I reckon the only way to check that is by camera.

So would it still run ok with dropped valve guide? And am I sticking the camera in the spark plug hole or am I looking in like the intake runner?

 

[mikez71]

I agree with Fless, get a good scanner on it.

Can it still have good compression with a dropped guide?

Kind of sounds like it might be electrical.. Plug wires? Dirty grounds?

 

[j91z28d1]

my camera, I think he means a bore scope.

I bought this one for home and use it more than I thought I would. I have one at work that costs way more but isn't nearly as useful.

VEVOR Articulating Borescope Camera with Light, Two-Way Articulated Endoscope Inspection Camera with 6.4mm Tiny Lens, 5" IPS 1080P HD Screen, 8X Zoom, 8 LED Light Snake Camera for Automotive, Plumbing | VEVOR US

Discover the VEVOR Borescope with a 6.4mm lens & 5" HD screen, offering 180° articulation, 8X zoom, and LED lights for superior inspection in hard-to-reach areas.

m.vevor.com

you can go in thru the spark plug hole, and turn it up to look at the valves.