2010 sierra 5.3 2468 misfire

[Levif]

Super random 2468 misfire. Backfires out of the intake. Only codes are p0300 and o2s. Replaced all 4 o2s today. While your driving, it will run fine. Then randomly start misfiring so bad it won't get out of its own way. Key it off then back on and it acts normal for a bit then back to bad misfire. Tested fuel pressure and it stays around 50-55 but when it starts misfiring the fuel pressure seems to drop like 10-15psi and the needle fluctuates fast almost like it's having a delivery issue. I tested each injector and each coil. But everything tests fine. just did cam, lifters, trays, pushrods, oil pump, vtc and timing chain in April. Replaced with all oem/mahle parts. Also have replaced tps. Been running normal until friday. It's super confusing. When it's misfiring I can unplug 2468 injectors and it doesn't affect anything. But when it clears up if I unplug 2468 it makes it miss. LTFT-25 ON BANK 2. Any help is greatly appreciated 

[Levif]

Note- intake gaskets were replaced with upgraded mahle gaskets when the top end components were replaced.

[CamGTP]

It's a wiring issue then. The hard part is finding it when it happens. If a whole banks goes out like that, it's a circuit problem.

 

Went through it on my dads malibu with a 2.4, the main power wire to the injector circuit had a bad spot in it. Took a little while and it would start misfiring on all cylinders and cut all power, let it sit and it would come back or if you moved the harness around. I had to repair the wire to make it stop.

 

Not saying yours is with the injector circuit itself but my guess would be one of the main power wires to the coils/injectors on that bank.

Edited February 7, 2022 by CamGTP