GEN 2 Cylinder 6 misfire

[mtbdad67]

I have a ‘20 with 85,000 miles on it.
It has developed a misfire on cyl 6. We have changed the plugs and coil packs and it is still there. We have done a compression test and checked the Ignition wires going to the coil packs. We can’t find anything. Any ideas? Engine has no mods and is super quiet while running. Oil and coolant look good exhaust smells strongly like raw gas.

 

[isis]

Cat going bad?

 

[CigarPundit]

Bad O2 sensor?

 

[nikhsub1]

Injector?

 

[mtbdad67]

Injector?

We have one ordered. We are going to try that tomorrow.

 

[mtbdad67]

If it was a cat or O2 wouldn’t it affect the whole bank??

 

[thatJeepguy]

If it was a cat or O2 wouldn’t it affect the whole bank??

Scope the intake valves for buildup.

 

[Zeusmotorworks]

Shouldn't be a problem with the port fuel injection, but worth a look. Maintenance and fuel will vary.

 

[Old-Raptor-guy]

We have been seeing a few engines, admittedly mostly 3.5 ecoboost with valves/valve seats that are leaking causing a misfires. Compression will be fairly good, maybe down 5-10psi from other cylinders. Leak down test will show it though.

Last one was about 40 days ago, 2019 F150 3.5 ecoboost, 95,000 miles. Customer is an older guy who used to be a driving instructor 25 years ago. He drives like an old grandpa, always runs Chevron 91 octane (highest octane we have here at 5000 ft elevation). Never let's it idle more than a couple minutes. Clearly not abuse in this case, I have no idea why and so does everyone else.

Removed heads, sent to machine shop, replaced all the one set of valves (all intake or all exhaust cannot remember which) reassembled and 100% golden.

Weird is all I can say.

Looking at the valves they almost looked octagon. Like they are not spinning enough.

 

[Zeusmotorworks]

So an initial manufacturing issue?