2013 Yukon 6.2 with p0304 code

Hello! Trying to pick your brain on my 2013 Yukon XL with 6.2L. Had the P0304 code with traction control light and stabilitrak lights come on. Engine light flashes. Got the vehicle home, restarted with no lights. Drove it 200 miles lights come back on and stayed on. Has AFM disabled with Black Bear tuner. New spark plugs last year. Plugs look good, coil packs look good, checked injectors last night. One looked a little different so swapped it, but still stayed on cyl 4 when rechecked. Vehicle idols rough after about 45 seconds but does not shut off. Filled up with gas in between light going off and coming back on- use premium. A couple years ago I put regular gas in it to get me home and threw a light. Hubby told me not to do that again! So I only use premium and synthetic oil. I just question if it would be a lifter if the light doesn’t stay on and drove fine in between. If I read correctly the lifter has a pin in it to keep it open with the AFM disabled. So I’m struggling with the thought of it being a collapsed lifter. Anything else I should try before pulling valve cover? Thanks!

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally assist you with your issue, but other members of this Forum much more knowledgeable than me in this area will chime in.

these lifters do still fail even with afm turned off in the tune. not that they release the pins and get stuck, but they will fail in other ways.

do you have any tapping?

do you have a scanner you can see data on? you can also swap a plug with another cyl or replace just the one.

j91z28d1 said:

these lifters do still fail even with afm turned off in the tune. not that they release the pins and get stuck, but they will fail in other ways.

do you have any tapping?

do you have a scanner you can see data on? you can also swap a plug with another cyl or replace just the one.

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Yes, I do have access to a scanner. Tonight my husband checked compression on cyl 4. At first it was getting pressure, then a few cycles later it did not, then the last time it had pressure again.

Budzy24 said:

Yes, I do have access to a scanner. Tonight my husband checked compression on cyl 4. At first it was getting pressure, then a few cycles later it did not, then the last time it had pressure again.

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sounds like it's time to pull a valve cover off and watch the rocker while cranking. but if you don't have compression, I'm guessing something has gone wrong with that lifter, even thou you have it turned off. why? I don't know.

if it does stop opening the valve. you could try the short cut the crazed performance guy does, and maybe it's somehow getting oil pressure to the lifter even thou it's off. maybe thru a leaking vlom solenoid. that requires ordering 20$ worth of stuff and removing the intake and vlom, that's pretty easy compared to pulling the heads but it would be a try, the real way is to pull the heads, either replace everything afm related with new oem parts or go with a delete kit, new cam and lifters.

Budzy24 said:

Yes, I do have access to a scanner. Tonight my husband checked compression on cyl 4. At first it was getting pressure, then a few cycles later it did not, then the last time it had pressure again.

Click to expand...

I am having the same problem with #4 I am not getting signal from ECU to coil. Pull the plug wire and put a plug in the end of the plug wire and start it and get out to see if you have spark. dont touch the plug or metal get insulated pliers and ground the end of the pkug and see if it is firing.

the stabilitrac and traction controls are being shut off by the ecu because of the misfire, they will go away when it runs right again.

Possible broken valve spring.

slyhog022056 said:

I am having the same problem with #4 I am not getting signal from ECU to coil. Pull the plug wire and put a plug in the end of the plug wire and start it and get out to see if you have spark. dont touch the plug or metal get insulated pliers and ground the end of the pkug and see if it is firing.

Click to expand...

Difference is, they checked compression. Had some, lost it, then had it again.

Pressureangle said:

Possible broken valve spring.

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I just replaced a broken valve spring on my 2013 Denali. Had it towed to a local shop that said they did diagnostics on it and gave me a quote for $5500 to replace the lifters. Told him I’d do it myself and had him tow it to my house. Spent 45 minutes removing the valve covers and found a broken valve spring. Got lucky that there was no damage to the valve or piston and got it back up and running.