Here is the story, I bought this truck for my wife as a mommy truck. Originally I thought it had a slight misfire, just needed a tune up. No check engine and I had test driven it for at least an hour. So I bought the truck and brought it home. The next day, she gets going down the road and the engine shuts down in the turning lane. The symptoms at the time were as follows:

Check engine code p0720
Blinking overdrive light on the shifter
slight misfire (feels like) in park and neutral
In gear it has an extremely rough idle unless it’s under a load
In gear if you sit for more than 10-20 seconds it just shuts down

So I changed the output shaft speed sensor, it didn’t fix this issue and still showed the same code. I read somewhere that an alternator can cause RFI (Radio Frequency Interference) and cause a malfunction, so I unplugged the alternator and it seemed to have fixed the issue. The next day I replaced the alternator and that fixed three things (temporarily).

1. The check engine light was gone
2. The blinking overdrive light was gone
3. It wouldn’t shut off anymore

But even then, still rough idle in gear and slight misfire feel in park/neutral. It was like this for several days, so I put a can of sea foam in the gas tank to see if maybe it was just bad gas or something gunked in the fuel. Now several days of no check engine light or shut downs, IT HAS COME BACK. What do I do?

Similar threads with some ideas

https://www.ford-trucks.com/forums/1...y-voltage.html


https://www.ford-trucks.com/forums/8...need-help.html

thanks Seville, it seems like I need to do the tune up and see what happens. I’ll let you know how it goes

Need more info - how many miles, any maint records, what's the fuel pressure look like at the fuel rail test port ....
You may just have several different issues from lack of maintenance.
First, fix the misfires before your cats get clogged.
It will take a lot of misfires to set a code so you need to look at the raw mode 6 data to see which cylinder/s are misfiring.
If it has a lot of miles you may just need a new set of boots for the plugs, the coils are probably fine.
Hopefully the OEM plugs have been changed if it has 100k or more and torqued to 25-28ft/lbs.
Have you checked all the vacuum lines for cracks, deterioration, soft spots, particularly the PCV hose where is connects to the throttle body.