Potius

If I had to guess I’m thinking cam lobe got worn down caused the pitting on lifter and wasn’t “lifting” it enough for the exhaust valve to work properly hence all the blackness on valve and exhaust port for cylinder 8 which was giving me the misfire. But again that’s only a guess until I get the camera in there

I thought of about the dod kit but I’m still hoping cams fine is good so I don’t have to mess with the other side lol

Not sure yet buying an inspection camera in a few days to look down the hole. Its cylinder 8 so too far in back to see by eye. Hoping cams fine. If so ill replace lifter and tray as well as clean up or replace the valves

188k

And finally a close up of the lifter from cylinder 8

Cylinder 6&8

Cylinder 2 and 4 lifters

Ok so I decided to not buy another part until I actually found something damaged or wrong. Unfortunately that only left valves lifter and cams to check. So had a fun day today in the cold(northern Maine here) and here is what I found so far: valve pic (cylinder 8 is the black valves)

Where do you connect a vacuum gauge on this engine? It doesn’t seem to have vacuum lines and I thought the brake booster line didn’t work for a gauge cause it goes directly to the vacuum pump and not into the engine

I swapped plugs and wires with 2 other cylinders to be sure and no change as well as checked for spark and it has it. I’ve literally checked everything

Ok sorry for the time since last update. Finally got parts/time so went to remove cylinder 8 injector and course rail was stuck so bent that coming out. Ended up just putting a new passenger side fuel rail and 4 new injectors in it. Changed intake gaskets just to be sure and put everything back together. Double checked everything and started her back up. Not a single change. Everything is exactly as it was before with cylinder 8 misfiring. At this point I’m about to change the HPFP mainly due to being stumped what else it could. A quick recap: spark plugs checked and verified there is spark coil packs checked/ moved with no change spark plug wires checked an spark verified compression test good on all cylinders took valve cover off and all rockers good and doesn’t look like stuck lifter at all checked for vacuum leaks and smoke tested Honestly if it’s not the HPFP then it must be electrical and I’m way out of my league

On a side note rock auto tells me the correct injectors are the nominal flow part # 12710481. It’s the only gm genuine injector listed so I assume it’s right lol

Due to the fuel lines being 1 time use I’m going to do the 1 injector on cylinder 8 due to getting almost no change in rpm’s during injector test and the fuel pump. Wish me luck parts should be here in a few days

Thank you for that link asilverblazer. Definitely helped me zero down some things. So went back to testing concentrating on the fuel aspect. My pressures seemed within range 45-60psi low side and around 700’s high side at idle. Did the injector balance test/correction and I believe all injectors tested within acceptable variance. I attached the injector balance numbers. Here’s the thing though when doing the test there was a noticeable drop in rpm when I did each injector which is suppose to happen. However when I did injector 7 the feeling wasn’t as strong and when I did injector 8 you barely felt any hiccup at all. Injector 8 is the one with 45k misfires and injector 7 has 950. Now with me ruling out most everything else and not having any lifter noise compression or spark issue etc would it be a safe bet to buy the 2 injectors for 7 and 8 and pick up a new hpfp. I figure it needs the injectors and with almost having 200k the hpfp should be around end of life so would be preventative if nothing else.

190k miles with no mods. Owned it since 105k maintained since then meticulously. No recent tune ups in last 30k other than fluid changes. Oh I did put a Rough Country cold air intake on it. As to the thread going to start reading it now and thank you for the link