At wits end. Persistent Misfire Only Under Load

[Bobmbx]

Getting a misfire on Cyl 2 only. Misfire only occurs under load; idle and cruise are perfect.

Changed all plugs and coil on Cyl 2, no change in behavior.

I'm stumped.

 

[Mbrooks420]

Did the number 2 plug look any different? Injector would be my next move. Which motor? Ecoboost? Miles?

 

[Bobmbx]

Did the number 2 plug look any different? Injector would be my next move. Which motor? Ecoboost? Miles?

Plug looked good (no different than the other 5).

3.5L EB, 110k miles.

 

[Exploder321]

The coil may be failing. With Coil On Plug (COP) it should be easier to isolate. Swap the coil with another cylinder and see if the problem moves with it. Check your spark plug gap which could be causing the failure. Also, if the spark plug has a crack in the porcelain it can misfire under load. I'm working through similar issues.

 

[tele2win]

Greetings! First post here...

A bit more on the coil and plugs... I see where you say you replaced it. Hopefully you did so with an OEM coil. I was formerly an ASE certified master auto tech in another life (work in IT now) and nearly every vehicle I ran across did *the best* with OEM tune-up parts. Here is an example of someone else still in the field who states the same: FordTechMakuloco - Don't Fall for the Marketing Hype: Aftermarket Ignition Coils are Absolute Junk!

Don't forget to put on a new spark plug boot on the coil while you are in there, and use a dab of silicone dielectric grease in the boot where it slips over the spark plug. If you can afford doing so, it might be worth replacing all of the coils and spark plug boots. When looking at boots check for wear (cracking, inflexibility, carbon tracks, crumbling) and replace if you see anything like that.

Also: FordTechMakuloco - 2011-2017 Ford 3.5L & 3.7 Duratec V6 Engines: Spark Plug Replacement

Consider the fact that the engine in your vehicle runs a bit warmer and under higher pressures in the cylinders due to the twin-turbo 3.5L EB v6. Those higher pressures and temps are going to cause more stress on the primary and secondary ignition system components. And the spark going to your plugs, like any other type of electricity, will seek out the path of least resistance. So if the coil(s), boot(s), or plug(s) have a weak spot from temperature/stress, the spark may not make it to the plug if it can find an easier path to ground due to component wear.

Hope this helps! Tele

 

[Bobmbx]

SOLVED.

One of the new plugs was cracked. New plug installed, misfire cured.

 

[The D]