P0301 and 0300 Codes

[hatinthering]

2015 Tahoe, just turned 200K mi. Upon brisk downshift/accel, flashing CEL and traction came on. This happened once or twice over the last couple years, cleared itself shortly after and ran fine.
This time it didn’t clear itself. CEL still flashing while driving, clearly missing/running poorly. Scanned and got codes 0301 always, and 0300 with it about half the time. Checked cyl 1 spark, coil is good. Pulled plug (Original to my knowledge), looked like crap. Replaced, cleared codes, and ran perfect for 2-3 days.
Then back comes the flashing light and same codes, and rough running with clearly a cylinder offline. Cleaned nee plug and Replaced injectors this weekend, still no joy.
Any ideas beyond the dreaded lifter issue? Honestly does not seem like mechanical damage to me….no ticking, and cleared completely (and ran perfect, albeit for just a couple days) after the plug change.
Pretty stumped on this one….

 

[Fless]

Can you look at individual cylinder misfires to verify that it's hole #1, or another one? If one cylinder is misfiring, pull the rocker cover to see if the valves are moving.

Hang on to your old injectors; they're likely OE and may be okay. What brand and source are the replacements? Aftermarket parts are not very reliable these days, and there are some fake GM and AC Delco listings on eBay, Amazon, etc. Best to buy name brand from a brick and mortar store.

Can you put a good scanner on it and do a CASE (cam-crank correlation) relearn to rule it out?

What value is the MAF reporting at hot idle, in g/sec?

What do the fuel trims look like?

 

[OR VietVet]

What @Fless said and I an curious as to whether you bought new or from previous owner? You said has 200k miles and plug #1 looked original? Really? In the future please remember that some ignition components are maintenance items and are not supposed to be replaced just because having a problem. Especially the plugs. They should have been replaced 2 times already at 200k miles.

Yea, get a scanner hooked up and get some live data info and also check for a vacuum leak. Also like @Fless said, lots of crap parts out there.

 

[hatinthering]

Can you look at individual cylinder misfires to verify that it's hole #1, or another one? If one cylinder is misfiring, pull the rocker cover to see if the valves are moving.

Hang on to your old injectors; they're likely OE and may be okay. What brand and source are the replacements? Aftermarket parts are not very reliable these days, and there are some fake GM and AC Delco listings on eBay, Amazon, etc. Best to buy name brand from a brick and mortar store.

Can you put a good scanner on it and do a CASE (cam-crank correlation) relearn to rule it out?

What value is the MAF reporting at hot idle, in g/sec?

What do the fuel trims look like?

Definitely Cyl 1, I will pull the rocker cover next to check valve movement. Hundreds of misfires on Cyl 1 mode 6, zero misfires anywhere else.

Will do on holding onto the old ones, good point on possible fakes...I did buy "allegedly" GM on Amazon. Clearly though at least the other 7 new ones are working fine since replacement yesterday, but no change on Cyl 1.

I do not have CASE capability, but I can likely track someone down who does after I do the rocker check, assuming all valves are moving properly.

Will need to see if my scanner will read MAF and fuel trims as well, after I check for proper valve movement. Sounds like that is the next step for sure.

Regarding rocker check- I hadn't done this yet only because I nave never had the tell-tale ticking at all (very familiar with the noise from my 05 Z71, 380K mi), and because the condition went away completely for a couple days after the plug change. Is it possible/likely that a mechanical lifer issue could be intermittent like that early on?

Appreciate your reply, Thanks!

 

[hatinthering]

What @Fless said and I an curious as to whether you bought new or from previous owner? You said has 200k miles and plug #1 looked original? Really? In the future please remember that some ignition components are maintenance items and are not supposed to be replaced just because having a problem. Especially the plugs. They should have been replaced 2 times already at 200k miles.

Yea, get a scanner hooked up and get some live data info and also check for a vacuum leak. Also like @Fless said, lots of crap parts out there.

Thanks for the reply! This was bought used at about 90K maybe 4 yrs ago. Agreed on plug maintenance, that's on me...

Will get full capability scan after valve operation is checked under rocker cover...assuming they are moving properly. Sounds like that is the next step for sure. Fingers crossed...