I have a 2016 3.5 Ecoboost with 208,000km on it now. Cold morning starts recently have sounded less than rhythmic and I threw a P0300 code with some cylinder misfires. Runs fine after warming up but it may be time for some maintenance. I replaced plugs and boots at 100K I believe so I'm wondering what might be the first and best step to fixing the problem now. Plugs again? Other things? Trip to the dealership for something more involved?

 

Could be a bad coil pack (COP). You'd need some diagnostics to determine which one, or you could just replace all 6 for about $200. But that's just my opinion, and I tend to throw parts at things before I'll break down and go to a dealer for help.

 

Yea, first I was planning to do the plugs and boots, coil pack makes sense as well. Maybe swap out the fuel filter. I should check what the realistic maintenance list is for my truck at this milage, just do that before things actually break.

 

The fuel filter is not serviceable. It's a lifetime filter, inside the gas tank.

 

Check for individual misfire codes. P0300 is typically multiple cylinder misfires. The individual codes will give you a starting place to look.

Have you ever cleaned the throttle body and MAP sensors? It's fairly easy and doesn't cost much except time.

 

Noted some hesitation/stumble under load pulling my 7000# trailer. Had the tranny serviced (3rd) time. Took it back out stomped on it. Got a flashing "check engine" light (tell-tale cylinder misfire indication). Had a code for cylinder #3. Ran my truck to 117,000 on the original plugs before this. Replaced the plugs and the coil packs. Stomped on it a bunch after that. No codes and it is back to driving like a rocket ship...Buy online at Autozone. Saved 20% over going in the store. Next day free delivery.

Tranny service was needed anyway, so I'm happy!

 

I had cylinder misfires on my 2015 3.5 EB. Mine were caused by a bad O2 sensor. There are O2 sensors on both sides of the exhaust manifold. My misfires were all coming on the same side. Got the 02 sensor replaced on that side by the dealer (after they argued with me about it). No similar problems until I let the spark plugs get too old!!!

 

I'm having some issues. I replaced the passenger side valve cover to one of those aluminum ones. Haven't done the other side yet but this side was the one with the really bad oil leaks. After I was done it was fine until that Monday when I went to work. On the way home half way through my 36 miles back, it began kicking like a mule whenever I needed to floor it a little. This truck I bought second hand after I lost mine in a car accident back in march. So some things have never been serviced on this 16 3.5 ecoboost. I wasn't seeing an engine light come on so I floored it for a minute or two before my exit and that's when I saw the engine light pop up but flashing. After some flashes it went away. Got home and scanned the code. Brought up that cylinder two was misfiring. I scanned via the torque app and the cylinder had misfired over 60 times. I swapped coils between one and two. It got better but the next day still some misfires I could feel. Worried something on cylinder two was killing the coils, I replaced the coil at #1. Drove smooth enough I could wait till the weekend. I then pulled the spark plug at #2 and even though I saw nothing cracked or broken, I could tell the original owner had never changed them. The truck has 141k miles. Anyway, I changed them and went ahead and replaced all the coils. While the truck is much better, I was still feeling some hesitation and the torque app was showing a small amount of misfires here and there. I played with the gaps on the spark plugs. They came at .28 so I opened a few to .30 but no more than .33. Cylinder number two showed 17 misfires within a minute or two. Brought it back down to .28. The truck is much better although I can swear at 1600 rpms on cruise it's not feeling as smooth. Am I asking for too much to see zero misfires on all cylinders or is it normal to see 1 or 2 during my commute?

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