2021 3.5L Powerboost Cylinder 6 Misfire Detected

[rack04]

While on a 6 hour road trip my truck would randomly misfire. It wasn't consistent and sometimes lasted ~1 min and ~10 min before returning to normal operations. The check engine light would flash during the short events and would stay lit during the longer events. The code was P0306. I topped off the fuel with 93 octane and on the return trip it only happened twice and that was 5:30 hours into the trip, so the majority of the time it was operating correctly. I initially assumed it was bad fuel and also thinking it was a coil pack or plug issue. Any history of this with these trucks?

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[FaaWrenchBndr]

I would pull the plug and take a look

 

[randc42460]

Just saw this video show up this morning which seemed somewhat pertinent.

 

[JoeRedFly]

I'd just replace the plugs with good ones (not fakes from amazon). I had the previous gen 3.5 eat plugs a couple of times like that.

 

[My 2ND Ford]

Just saw this video show up this morning which seemed somewhat pertinent.

He puts out a good video, but a lot of 2021 3.5 still have the tapered seat plugs. The op should pull a plug to confirm what he has.

 

[My 2ND Ford]

While on a 6 hour road trip my truck would randomly misfire. It wasn't consistent and sometimes lasted ~1 min and ~10 min before returning to normal operations. The check engine light would flash during the short events and would stay lit during the longer events. The code was P0306. I topped off the fuel with 93 octane and on the return trip it only happened twice and that was 5:30 hours into the trip, so the majority of the time it was operating correctly. I initially assumed it was bad fuel and also thinking it was a coil pack or plug issue. Any history of this with these trucks?

It could be a failed plug, pull one and take a look. It could also be a failing coil which would explain the intermittent misfire. You didn't say how many miles on your truck! I believe the Powerboost has plugs scheduled to change at 60,000 miles.

 

[rack04]

It could be a failed plug, pull one and take a look. It could also be a failing coil which would explain the intermittent misfire. You didn't say how many miles on your truck! I believe the Powerboost has plugs scheduled to change at 60,000 miles.

Good point. I have 76K miles on it.

 

[bajaleo]

While not a PB, my 2021 EB truck had a similar misfire situation. I posted about here.

https://www.f150forum.com/f129/2021-3-5-eb-misfire-mystery-560848/

 

[rack04]

Just to update this thread. I tried to replace one part at a time to identify the issue. Replaced the Cylinder 5 spark plug and the issue still persisted. Replaced all 6 spark plugs while waiting for the coil pack and the problem still persisted. Replaced the Cylinder 5 coil pack and drove 250 miles without issue, so I'm confident the coil pack was the culprit. Now I need to decide to replace the other coil packs or just keep on keeping on.

 

[bajaleo]

I've considered buying a spare coil pack and carrying it in the truck with the tools to change it if necessary.

 

[rack04]

Well, unfortunate update. Took the truck for a 2-hour road trip and it's still misfiring on cylinder 6 according to my cheapy ODBII scanner. I have already made an appointment at the dealership so hopefully they find the culprit.

 

[DadBald]

Why would replacing the ignition coil on cylinder 5 fix the misfire on cylinder 6? Or typo?

 

[Calson]

The first step should have been to check the spark plug wires with a VOM. There are specifications for the Ohm reading from plug wires and if a wire is out of spec then the decision is whether to replace the single wire or all the plug wires.

When cars were introduced with Cat converters and ran at higher temperatures to reduce fuel emissions, overheating was a common problem and this extended to baking the insulation of the plug wires. Testing the plug wires used to be commonplace but this has been forgotten.

If a coil is not producing sufficient voltage it would affect all the cylinders and not just one. It would be most noticeable when accelerating where a weak spark will cause the engine to "stumble".

We have so few mechanics that are able to diagnose auto problems and so they replace part after part until the problem seems to be fixed. They cost their customers a great deal of money in the process.

 

[dochawk]

If a coil is not producing sufficient voltage it would affect all the cylinders and not just one

Not doubting you, but curious: since the coil is generating that voltage, how does that carry over to the others, which generate their own? Firing late or weak, causing others to fire wrong based on the actual rotation rather than what the computer expected?
?

 

[bajaleo]

This is for the previous gen but the diagnostic method still applies.

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