Following up to my prior post as replacing the alternator did not seem to work. 2011 5.0 SC with ~65k miles

I feel misfires (not enough to trigger CEL) on both startup, when revs drop to idle, and when braking hard, and the transmission downshift. Sometimes this lights up my dashboard with MIL and Battery icons and stalls.

My LTFT on both banks is 7% at idle, and around 3-4% at both 1500 and 2500 rpm. At some point this obviously triggered the CEL for too rich.

Any recommendations on what to do next?

 

Recent related services include new spark plugs at 59k, new air filters at 61k, valvoline fuel system cleaning at 62k, brand new fuel injectors (for 1, 3, 5, 7) at 62k, metal intake replacement at 65k. Car has a brand new battery and new alternator.

 

I don't know and you have certainly done a good bit of work on this already!
But on my old S Type R those two codes were always related to vacuum leaks in the intake system. It looks like you replaced the factory plastic intake with an aftermarket metal one?

Can you monitor the fuel trims in real time and use Propane or carb cleaner to spray around the engine looking for any leaks? Maybe focus on that metal intake?
Since the fuel trims get better at higher RPM's this indicated the vacuum leak is fixed and does not get worse with higher engine RPM's.

Any work been done where the intake manifold has been removed?
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I think it would be P0171/P0174 for vac leaks.

Too rich might include bad MAF, wrong injectors when changed.

 

This ended up being something stupid. I had replaced my intake with an aluminum intake. One of the connectors slipped off and was likely restricting airflow. Replaced, made sure everything was nice and tight, and after a drive cycle or two, fuel trims are back to normal, and not one sign of a misfire.

 

Hey that's a easy and cheap fix so you won that one!
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Thanks for the follow up.