2012 F-150 Super-Crew 5.0 Automatic, 2WD
90,000 miles I'm NOT a hot rodder. I'm mostly on the freeway, I roll fast but I get there slowly and smoothly. I don't believe the gas pedal has ever hit the floor, as I don't drive like that.

The saga:

Zero problems until....
200 mile drive
Sat overnight
Started the next morning and there was a lot of noise, tinny sounding like a heat shield rattling, that grew quieter and stopped after about 10-15 seconds
Drove it locally, parked and when I returned all was well - no noise
Parked again for the night and the following day the same rattling that cleared as before
Following day same thing. Returned 200 mile drive and parked.
Following day, same again. Put it in the garage for the night.
Next day got under it and poked around, rubber mallet looking for the heat shield or whatever else. NOTHING out of the ordinary.
I should note that I found the noise to be coming from around the transmission area, but couldn't isolate it further. It did not appear to be coming from the engine itself.
Following day same thing, except the rattling would recur and stay between 1500 and 2000 RPMs. Constant in that range.
Following day, drove to work. Same noise on startup, but didn't clear. Got to work and noise was constant at all RPMs, and seemed a bit louder. Enough that it was embarrassing to drive through the parking lot.
On the way from work I ran over a pothole and jarred the truck as potholes do. The rattle stopped immediately. Completely gone at all RPMs.
Either very good or very bad. (Spoiler alert - BAD)
Drove about 10 miles, met a friend, dropped off a part he needed for a project. Truck was idling fine, started fine, smooth and quiet as it has been since new.
Parted ways, pulled from the parking lot, and all seemed well.
Suddenly, a marked loss of power. Could barely accelerate to 60 MPH, and was getting progressively worse. The engine light flashed, and cleared based on RPMs.
Limped along and took an exit, slowed of course, and it wouldn't re-accelerate beyond 30 MPH with the engine light coming off and on as RPMs raised and lowered.
Limped into a parking lot and called for a tow.
The dealer pulled the codes and found nothing at all other than misfiring 5,6,7,8. Compression is great. Plugs are great. Etc. They're completely stumped.
Disclaimer - I know nothing of modern vehicles.
They called me to the dealership to discuss, and the tech suggested new plugs, despite his own assertion that they looked like new. As a matter of fact, they thought that I'd had them replaced recently, but no one has ever worked on this truck other than oil changes.
Next was the offer to swap the coils from 1,2,3,4 to 5,6,7,8. In my ignorance of modern vehicles, I didn't realize that each cylinder has a coil. Oops. From what I can glean, the likelihood that all 4 are bad is nil and none. Do they cascade in series? If 5 quits, does it take 6,7,&8 with it? I've no idea.
Anyway, that's where I am with it. Hopefully, someone has some additional insight to help me suggest things to these guys.

 

Now there's a pet peeve of mine, a shop that overcharges for incompetent technicians. Your problem is the driver's side catalytic converter needs to be replaced. When a CC breaks internally the honeycomb moves around, rattles, and eventually clogs the exhaust flow. The clog is what's causing the loss of power and misfiring on that bank.

 

Not a 6 speed..... there is no other transmission from 2009-2014....so what is your transmission?

 

I suggested that EXACT thing, and they said no, it's not throwing any cat codes. I even told them about the old potato in the exhaust pipe prank from back in the old days. Apparently, if there's not a code, they're stumped. As you said, incompetence. Honestly, it seems to be a trend, at least with Ford techs. I took a Focus in because the clutch pedal return spring up under the dash had broken and fallen on the floor, so the pedal wouldn't return to the top. I took it in to the dealership, but didn't tell them about the spring. They diagnosed it as needing a new clutch, as mine was trashed from a valve cover oil leak (small) which had ran down the engine into the transmission and ruined it. I asked about running through puddles or on wet roads and water getting in the same holes, and they told me it does, but the rust it causes is good rust. THAT is the honest truth. I raised hell many levels up the chain, and it did me no good whatsoever. I didn't get the clutch, didn't want the clutch, didn't need the clutch, but I got a $3 spring instead of an $1100 clutch.

 

If that's the case, it's a 6-speed. Thank you. Another forum differentiated the 6-speed as being atypical. I don't know, nor do I care, as I don't work on these over-engineered nightmares. In my estimation, if it was made after about 1971-1972, it's disposable junk anyway. Truck today, soda cans tomorrow, and truck again in 6 months.

 

-MISINFORMATION- The 4-speed transmission (4R75W) was available for the 2009-2010 4.6L 2V engine combination.
.

 

ok... now I know

 

Just to close out the post, it was indeed the catalytic converter internals had collapsed. I had to make them stop their bumbling diagnostic attempts and insist that they check it immediately. At the end of the day, it was $1157.00 out the door. Ridiculous, but after nearly 3 weeks I just needed it back.