2011 f-150 3.5l GTDI misfire under load

Hi guys. I need some direction with this one. The truck is setting p0302 and p0305 under heavy acceleration. data shows primarily cylinder five misfiring. Only history I have is the truck has had all six ignition coils replaced and all six spark plugs for these same two codes. I`v inspected spark plugs and coils for carbon tracking cracks gap etc. I performed the fuel injector flow test with scan tool and it is 158 normal is 160 +/- 15 Engine cranks like it has good compression and also performed ford`s relative compression scan tool function and found no problems there. Im really not sure where to go next. I`v tried the wiggle test on the wiring harness and found no issues. I need some direction. The only way I can duplicate it is to drive it and heavily accelerate once already going about 25 and i can feel it misfiring badly. Not sure what to do If I should run wires through the hood to scope injector or secondary ignition under load... three wire coil so cant look at primary side. only related technical service bulletins I can find dont REALLY apply. I`m in Arizona and the one bulletin says if its not humid / damp then the bulletin does not apply. But it also addresses the misfire under load symptom... TSB 13-08-01 - Effective Aug 5 2013
2011-2012 F-150, 3.5L GTDI - Intermittent Stumble/Misfire On Acceleration From Highway Cruise In Humid Or Damp Conditions, Possible P0304,P0305,P0306,or P0430

Hey ptebo1! I've seen that TSB before... Has something to do with replacing the charge air cooler with an updated version, correct? I always consider it when I have one of these misfiring, but have yet to see it genuinely apply.

I'd suggest a few things. First off, use the scanner to perform the crankshaft variance relearn. It's under Functional Tests, and will have you snap the throttle several times in Park. Then, clear the codes and go for another test drive. See if the same codes come back. It's been my experience on the 3.5L EcoBoost that the misfire monitor will easily flag the wrong cylinder, which gets resolved with a relearn. Chased my tail with this before. :silly:

Second, depending on which codes you get back after the crankshaft relearn, I'd suggest moving plugs and coils around. I see that they've been replaced, but the high cylinder pressures made these very sensitive to ignition problems. Plus, the 168% Engine Load at the time of the misfire says there was some boost at work.

I also saw that you inspected plug gap. I really don't mean to nitpick, but did you actually measure the gap with a gauge? Been there before, too. :lol:

I didnt actually measure the gap. Today I had the guy come to where i work and i updated the ecm with ids per tsb and i stuck a piece of cardboard over the bottom eight coils of the intercooler with double-sided tape instead of buying fords foam piece to cover it. Im going back to his house when i get out of work. first thing ill do is swap coils, plugs and check gap per mfg spec. if that doesent work im going to take the intercooler off and see if there is any condensation inside of it. did i mention it is throwing the same 2 codes as before the plugs and coils were changed? Ill post an update later tonight when i get home in about 3.5 to four hours. I havent heard from him since i updated the pcm about 3 hours ago. im hoping its fixed... Thank you Tyler for responding.

Ok you were right Tyler. I went over tonight and the first thing I did was remove the intercooler expecting to dump out a bunch of water from it. I was thinking that under load the turbos put enough boost to push enough water to cause the air/fuel mixture not to ignite. Not even a drop of water came out of it. I looked up the spark plug gap with ford tech info spec is .028 - .037 - I pulled cylinder 5 spark plug to check the gap and found that it was gapped at .050.. (( The guy also told me that the auto zone guy looked up spec. and gapped them all for him )) almost double factory spec. So I re-gapped all of the plugs to .028. I re-installed everything. swapped #4 and #5 ignition coil - performed the misfire monitor neutral profile or whatever ford calls it procedure. test drove the vehicle under the same condition which I was able to duplicate the misfire before and it is completely gone!! I cant reference them off the top of my head but I know scanner danner has some great secondary ignition videos where he explains higher cylinder pressures making it harder for the spark to jump the gap. That explains why this engine has such a small gap size at .028. Honestly I dont even think I would have brought my spark plug gapper had you not responded to my post. Thank you very much Tyler. What a co-incidence that the same two codes popped up before and after plug and coil change though right?

Hey, great to hear it's fixed! You're right - VERY misleading to get the same codes back after the coils and plugs. I think just about anyone would be thrown off when they saw that. Honestly, I was kinda hoping you'd find an intercooler problem? :lol: I think it's a really interesting phenomenon that's being described in that TSB, but still haven't seen it happen.

To be honest, the only reason I went towards spark plug gap was because I had a comeback due to the same thing. :blush: Been told for too long not to check gap on platinum/iridium plugs, so I slapped a set in a 3.5L EcoBoost and immediately had problems. Now I know better. :silly:

You're right on about what Paul said regarding cylinder pressures and the misfire. I honestly think if this was a normally aspirated engine, it wouldn't have noticed the inconsistent gap at all. But it's boosted, which means it puts a lot more stress on the ignition system, and exposes any weaknesses much sooner.

Hey guys, just wanted to thank you for this info.
I’ve been all over trying to solve this issue for about 3 months. I was inclined on a vacuum leak before I saw this.

First thing I did was changing the plugs, so I never imagined the problem would still be there.
Everyone I’ve asked says they would’ve never imagined that the gap for a truck this size would be so small.

Thanks again!

Thanks for the reply! For our info, what brand of plug was installed in yours?

I had (and still have but with the correct gap) the NGK LTR6BP with .04 - .05 gap.

I went to a local workshop (I’m from Chile) for an oil change and asked them to change the spark plugs because I was having random misfires under load.

I’m planning on going later today to ask them why they installed those without asking first, and why didn’t they check on the gap tech specs since I told them I was having a combustion issue.

Usually I do this kind of work by myself, but I tried to save some time since it’s a rather simple job.

Gotcha, thanks sir. Every NGK plug I've seen for this engine isn't gapped correctly out of the box. Motorcraft is always correct the first time. Now I just recommend Motorcraft from the beginning. :lol: