Bank 1 Misfires, Very Rich
 

I've been working to diagnose bank 1 misfires on a customer's 2018 F150 5.0, and I cannot figure out where to go next with this thing. I started with the obvious stuff (coils, IMRC, injectors, etc.) and nothing has changed the misfire. It's primarily cylinder 1, but based on a power balance test it seems cylinders 2 and 4 are contributing the least. Fuel trims are pretty far negative, around -16- -25. Bank 2 looks perfect, no issues over there.
I pulled the intake manifold to see that the runners are in tact and operating, and everything looks good in there. I pulled the vacuum line for the actuator and manually ran them, and while one bank seems to close faster than the other, they both operate smoothly.
The only codes to set are P0300, 301, (occasionally 302, 303, and 304), and P0316 (misfire at startup, first 1,000 revolutions). Cylinders are getting spark, fuel pressure looks good (although the commanded pressure is occasionally around 100 PSI shy of the actual pressure... is this normal?). Upstream O2S are responding from what I can see, with the bank 1 sensor bouncing around VERY low amperage (-50mA) and coming back up to normal values (closer to zero, with occasional jumps into positives). I'll be honest though, I don't quite understand how to diagnose these wideband AFR sensors like I do with old school narrow band sensors.

Anybody have any idea where to go from here?


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Codes 300 and 316 are of more concern.
All 4 Cylinders on Bank 1 are seeing the effects of the root cause.
Seems injection amounts are way in excess. there may even be Gas in the oil, now.
The up stream Ox Sensor is detecting this and shifting the long term table Lean trying to account for it and should have code 172 set for Bank 1.
The 5 lead Ox Sensor actually is designed to measure Air to Fuel ratio in the exhaust gas directly at the Sensor and report it directly to the PCM to control fuel pressure from the Pump and it's controller Plus injection pulse width control from the Table..
Look at an official Ford DTC list and description of these two codes and their possible causes.
The problem may be where your not expecting
Fuel control, Map Sensor contamination, Pump control module, fuel Pressure sensing Bias, Crank Position-sensing etc.
Good luck.

Which injectors did you change

I swapped the port injector on cylinder 1 to cylinder 5 when I had the manifold off to check the IMRC flaps.

I double checked the fuel pressure actual vs. commanded yesterday, and it looks like it's actually pretty consistent when graphic them. It appears to be the normal delay in data transfer as far as the actual pressure catching up with the commanded pressure.

I'm going to check the crank sensor signal today, along with the O2 sensor. I have a feeling that although I don't see any symptoms of a clogged cat, it may still have one. The customer had replaced the cylinder 4 coil with a Duralast (that was my first assumption of the problem, aftermarket coils are garbage) but I feel that he may have run it for some time like that. With how rich it is, it could very well have done some damage... it certainly smells sulfur-y.
When I measured the cat temps, I had about a 100 degree delta on bank 1, but bank 2 was around 40-50 degrees COOLER post cat. Very strange, especially since bank 2 seems PERFECT based on trims and cylinder contribution. I did a basic vacuum test and vacuum looks good, no restrictions evident based on that.

I also remembered, the ONLY thing I was able to improve by playing with scan tool data was when I commanded the purge valve on. The higher the duty cycle, the more the misfire data calmed down. When I went back to 0%, cylinder 1 started misfiring more again. I have a feeling that's only because it was further leaning out the mixture.

How does it act at part throttle when the direct injectors take over,

This appears to be a BANK 1 ONLY issue - so can ignore things that are associated with Bank 2 stuff or common to 1 and 2..

Yes, it's definitely specific to bank 1. Bank 2 seems to be perfect.
It seems to slightly improve, but not completely.

FWIW my experience has been the rich side will always be cooler especially in an aluminium engine. Ya got quite the issue there, check all your grounds and connection pins for corrosion and battery for stable power. You may have done that but just thought I would add it. Good luck man.

Check and unplug the bank one o2 sensor, before the cat, and see what happens, i just watched a youtube short, where the wires on the bank 1 sensor 1 o2 sensor rub on the insulation.

Will do! That's interesting. Wouldn't surprise me if that's an issue here. It's not pegged in either direction, but it could have a slight short to voltage or ground.