JonMarkTX

The only symptom I’ve experienced is an annoying misfire that occurs around 42-45 MPH of sustained speed (never misfires on acceleration). But recently it’s started to misfire at idle very sporadically (like once a month) while I’m waiting at a red light. Tonight, I pull into a restaurant to pick up a to go order, put it in park, and my truck starts to shudder (similar, but a bit more pronounced than a misfire), and then it just shuts off on its own. I restart the truck, still sitting in park waiting for our order, and every 30 seconds or so the truck will shudder rumble again (it hasn’t turned off again yet). But it’s definitely never misfired/shuddered this often. Not throwing a code/CEL yet.

Things I’ve done about 10K miles ago to address earlier misfire: replaced spark plugs, coil boots, and cleaned fuel injectors.

2016 King Ranch 4x4 V8 with 105K miles.

Any thoughts?

Rolling Thunder

Take it to a professional instead of throwing parts on it.

FordGate

Have you replaced the COPs?

William Maxfield

VCT issue. either solenoids or phasers. it will eventually throw a code in the range of P0011/12 P0021/22

adaycj

I'd say it needed plugs and boots at 100k anyway. Plus it is awful hard to diagnose engine driveability problems with worn out ignition parts on the truck.
A scan tool with real live PID data is your friend here. Looking at fuel trims, misfire data, and other things will seriously narrow down the culprits. That may require that you visit a shop if you can't make the investment in your own. If you will actually get a pro that can diagnose the problems when you get there is anyone's guess. Most shops near me just throw parts at it. And that may be after a month wait to get in. Sad but true.
As a next step, if you can get your hands on wiring diagrams with ground numbers and a component locator that shows the ground locations; I'd inspect and clean every ground you can find, especially any that might be stressed when you go from P to R or D. It's pretty much free and will eliminate another potential problem source.

SpencerPJ

For dummies like me, COP stands for coil over plugs. My first thought is a dirty throttle body.

dodgeman1

How exactly did you clean the fuel injectors?

JonMarkTX

yes, COP’s were replaced when I replaced spark plugs, however it wouldn’t be the first time that a coil pack was faulty when brand new, so I’m kinda just waiting for a code to tell me which one it might be … and I cleaned the throttle body at the same time as well (but maybe the throttle body is just failing?).

Bluegrass

Your describing a classic Coil failure.
Use a Scanner to look in Mode 6 and test numbers in the low 80 area for the misfire records and see if one cylinder is the cause.
If yes, replace that coil no matter if you already did do.
The failure type does not set code because it comes and goes which causes cancellation of the code.
Good luck.

JonMarkTX

UPDATE RESOLVED: I was very, very hesitant to update this thread with the fact that the misfire issue has been resolved because it seemed way too good to be true from a very, very simple (and free) fix. To recap, I've been experiencing a misfire at coasting between 37-42 mph while maintaining speed - NEVER while accelerating. I would also experience misfiring at idle, and once the truck shut off on me. This had been going on for almost a year, and it had been driving me crazy trying to track it down. Finally, when speaking to a friend of mine he said that since it never happens while accelerating that maybe it doesn't have to do with the fuel side of misfire, but more so on the air side of misfires and asked about the throttle body. I told him I had cleaned it early on (around the time this misfire started), so I hadn't touched it since. He then asked if I recalibrated the throttle body after cleaning ... to which I replied with a deer in the headlight stare.

He told me that it's always good to recalibrate the sensor of the throttle body anytime it's serviced or replaced, otherwise the timing could be off and the wrong mixture of airflow would possibly be going to the engine, thus causing a misfire/stuttering. I thought it was too simple (and simply, quite dumb) to try. But I did it. I did the recalibration procedure (slowly depressing accelerator then releasing, turning off key, then repeating three times). Lo and behold the misfire has totally disappeared. Of course, I thought this was coincidence, but it's been a little over two weeks since doing that, and I've been coasting a lot in that MPH range to try to force it, and it's been as smooth as can be.

I had no idea that this could actually have been the cause. And I feel quite ignorant for not knowing to do that recalibration. So, hopefully my ignorance can help someone else in the same boat.