'21 F150 5.0 misfire

[Mwiseman1987]

Good evening everyone.
2021 F150 with 5.0. I bought it a year ago with 25k miles. Currently has 61k on it.
It's always idled rougher than I'd like, but i figured it was the cylinder deactivation.
Last week, CEL started flashing at a stop light at idle.

Checked codes with Forscan

Cylinder 8 misfire
Misfire detected with low fuel
Misfire within first 1000 revolutions.

Moved coil from #8 to #4 - No effect.
Changed all 8 plugs. No effect.
Running scan data, commanded lower injector pressure was at close to 3,000 psi. Commanded was at 799.
If I rev it up to about 2k rpm, the commanded and the actual run in line (I suspect its because the lower injectors don't run at idle?)

Are the upper injectors on these known to have issues?
This is where I'm leaning for the issue to be, but wanted to get other opinions.

Thanks,

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[JExpedition07]

I will attach the PI-DI blending charts for the 5.0L V8 below. The direct injectors do fire at idle if the engine is cold and should command around 40% at the low end. Once the engine is warm correct, they should not fire much at idle until you put load on the engine. I have seen a few isolated cases of leaky direct injectors causing an over-rich condition with misfires on earlier 3rd gen motors.

Cold PI/DI Blending

Warm PI/DI Blending

The more load detected, more direct injection is commanded pretty much across the rev range.

 

[Mwiseman1987]

Thanks.

I will add that the misfire does not appear to be present on a cold engine.

 

[JExpedition07]

Ah, yes. I’d take a close look at the injectors on that cylinder if that’s the case.

 

[Mwiseman1987]

Just thought I would give an update here.
Truck has been at the dealer for about 5 weeks now. Compression on #8 was 10-15% below the rest of the cylinders.
Cylinder head was removed, and leak down test was performed.
It was determined that it needed a new cylinder head on the driver's side.

New head has been delivered twice now. Both times has had the correct part number on the box, but the wrong part has been inside.
Dealer has put a case in with Ford, so we'll see what happens.

 

[Mwiseman1987]

Good evening everyone,
Finally picked my truck back up from the dealer yesterday, and I didn't realize how much I missed it. I will say that 6 weeks at the dealer was too long, but I can't point my fingers at the dealer for this one. Twice, the wrong cylinder head was shipped (Correct part number on the box, wrong part in the box).

Truck runs better than when I bought it. What I always thought was the MDS causing the rough idle must have been something that I've been having an issue with for 30k miles of my ownership.

I was told that this was apparently a "rare" case, so hopefully I'm not replacing the passenger side head anytime soon.

 

[gagliano7]

Just so you know cylinder deactivation doesn’t happen at idle.

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