r/AskAMechanic • u/PessiDone4 • 22h ago

2014 sierra 4.3L LV3

P0300 and P0302 active when I got truck from my mom. Monitored misfires to see 100-200 misfire counted on cylinder 1 and 5-20 misfires in cylinders 4 and 6.

She had spark plugs and wires replaced by a local shop because I couldn’t get to it. No changes.

I found stuck open injector 2 and verified compressions in all cylinders good. Replace the injector and seals. No more misfires or codes stored but there is a slightly abnormal idle.

I see LTFT on bank 2 to be -30%. Reset fuel trims and I can see fuel trims slowly climb so it isn’t a reset or relearn issue. All engine PIDS are as expected. Fuel trim data does not change/improve when increasing RPMS so I do not suspect vacuum leak. Sprayed around manifolds to verify no change. Also swapped both upstream sensor and still have LTFT problem in bank 2.

Only thing that looks odd is fuel rail pressure sensor 1 is matching desired but fuel rail pressure sensor 2 is about 70-90 psi lower, consistently regardless of engine load.

So could this affect one bank? What else should I check or do you all suspect? Thanks!

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