Mustang71

I would fix the misfires first, then look at fuel trims

bmdubya1198

They're going hand in hand in this case. All cylinders on bank 1 are misfiring based on codes, power balance, and misfire tests.

bmdubya1198

I've isolated the actual misfire (or primary misfire) to cylinder 4. The plug is very black and fuel-y. I cleaned it, swapped it to another cylinder, and the new plug for cyl 4 is already black again. Definitely the problem cylinder.
I swapped the port injector to a bank 2 cylinder today, no change. I did some more testing on the scan tool with killing injectors, running it on DI only and PFI only, actuating the IMRC (fuel trims on both banks went negative when activated, leads me to believe they are working properly on both banks), raising and lowering the fuel pressure, and nothing made any difference.
I'm starting to think that there is an intermittent drop out in the coil driver in the PCM, or something of that sort. I cannot find any mechanical issue with cylinder 4, or any of them for that matter.

Mustang71

Have you checked compression on that cylinder

bmdubya1198

I have, it was around 215 PSI or so.Very healthy.

After searching around some more, I saw someone that had an upsteam O2 sensor wire rub through on the heat shield and cause these issues. I'm thinking that may be a possibility, as when I removed that sensor to do a cat back pressure test, it ran much better. I'm going to unplug it and check it out today, fingers crossed I finally find something.

bmdubya1198

I unplugged the upstream O2S on bank 1, and now looking at the power balance, cylinder 4 is certainly the culprit. I then logged the cylinder 1 and 4 coils on my oscilloscope, and the graphs looked nearly identical. I had also previously checked for spark with a spark tester, and it looked very good and consistent on cylinder 4.
The only thing I can find that looks out of sorts is the fuel pressure. It's a bit higher than the commanded pressure. What I'm thinking is that maybe the direct injector is sticking open a little bit? It usually starts misfiring at idle after revving, so maybe the DI sticks open even after it switches back to PFI?
As I said, I've already done a compression test, so I don't believe there are any issues with the valves or anything mechanical.Spark is good, and I already swapped around the port injectors. So at this point, it's really looking like it's down to the direct injector.
I'm gaining confidence in this theory the more I think about it, let me know what you all think. I'd tear into it and swap it to another cylinder to check it, but I'll have to run it by the customer first before I do way more work that I'm already probably undercharging for.

ModularFord

Are you sure the direct injector isn’t getting stuck open and flooding the cylinder at low rpm? The port injectors don’t do a majority of fueling, they are more a supplement to the direct injectors. Port injection is only primary at low load, every increase in rpm is more and more direct injection engagement. If the direct injector is stuck or dribbling fuel at low revs where it should not be you will foul plugs.

bmdubya1198

That's exactly what I think is happening. I think that it may be sticking, especially after coming back to idle and over-fueling the cylinder.
That video looks like he had a very severe case of this. I think this may be only occasionally sticking. Cylinder 4 plug is very fouled, and smells of raw fuel every time I pull it out to check it, even after swapping plugs around.
I think what I'll do next is stick my borescope in there and run the fuel pump to see if it's leaking. I didn't notice any pooled fuel the last time I checked, unless I'm forgetting.

bmdubya1198

I'm happy to report that the truck is now running great! 8 new Motorcraft direct injectors is all it took... fortunately the owner opted to replace all 8 rather than just the one to hopefully avoid this in the future.
As far as diagnosing it, after running the truck, I had pulled the cylinder 4 plug out and stuck my borescope in there. Sure enough, the injector was dripping fuel, and within a minute or so, it was pooling on the top of the piston. That'll certainly cause a rich misfire. Test drove it, idled it, revved it, and it's silky smooth now.

Bluegrass

This is why I run Regain fuel cleaner with P.E.A. in it as the cleaner of choice about every other tank fill.
When I let it go too long, idle begins to show some small ripple, at times.
Idle is so smooth, a look at the Tach to tell if the engine is running.
2018 5L with over 86k miles and it passed oil at one time up to 45k miles until I found out why and what to do about it. No oil passage for more than 50k miles on 5w20 MC Blend at 5k mile change intervals. No dealer intervention of any kind, on the past oil usage issue.
Good luck.