1997 F150 4X4 4.6 engine with 285,000 miles

Truck was running perfect down the road, then suddenly it lost power and started missing at all RPM ranges. So i keep driving another 6 miles and then POOF the miss is gone and truck runs perfect. Couple hours later i hop back in it and its running good and then suddenly it starts missing and loosing power again except this time it never started running good again. Never did throw a CEL.

I hooked up my SCT Tuner (for my F250) to check for codes and came up with P0171 which indicated one of the banks was running lean, but no missfire codes. Did a search on here and learned the common problems(vacum leak) of that code.

Found the vacum leak at the PVC elbow, so i replaced both ends of the plastic tube.
Pulled the throttle body elbow and cleaned out the clogged up EGR ports.
Put a new air filter in and took the MAF out and cleaned it with MAF cleaner.
Put it back together and it idled way better but still ran like crap with the bad miss/sputter. Ran it down the road a few miles and came back thinking of the catalytic converter, i crawled underneath and it was glowing red. It does run and feel like the converter is stopped up but if i have a dead miss and dumping fuel wouldnt that make it glow red to or no? Still no CEL and now no codes.
Also i held the engine at about 1000 rpms where i could here the miss good and unplugged the fuel injectors one at a time to see if that made a difference. Each one i unplugged made it miss worse, so wouldnt that tell me that all 8 cylinders are firing?
Oh and i changed the spark plugs (motorcraft) 250 miles ago.

So it still cranks and runs smooth after a cold soak overnight and then after a mile of driving or less it starts the dead miss/sputter and loss of power. Hoping someone has had this situation, i hate to start throwing parts at it.

 

seem like you're doing well trying to run this down.

did you clear the codes after vacuum leak fix?
Did you change the fuel filter??
have tested the fuel pressure? give that a whirl after the new fuel filter.

If this still persists after fuel filter and pressure has been checked ...then it might be down to the a weak COP or two?

 

Yes i did clear the codes after i fixed the vacum leak.
I wanted to try the fuel filter today but it doesnt look like i will have the time to work on it.
Also this year model doesnt have COPs, it has plug wires and 2 coil packs. I dont think its spark related because i had it running as i unplugged each fuel injector one at a time listening and each one made it run worse. Seems more like some kind of sensor that quits after its been running for a few minutes and only when the motor is cold.
Anyone had this problem?

 

If you had/saw a red cat 'cover' not the actual cat housing, in day-light the Cat is melted, and likely plugged the flow a huge amount and needs to be replaced.
From this you should have a code 420 set at some point indicating the cats are no longer performing within limits and the sensors cannot even detect it..
The front and possibly the rear OX sensors could be melted as well and cannot control the fuel, and power is way down from the plugged exhaust and missing cylinders..
This all happened from one or more cylinders on that banks missfire and allowing raw fuel to pass on to the the cats where it burned at such high temps it melted the front cat at more than 1200 degrees, it is not meant to work at.
Fix the missfire before replacing any cat assemblies or it will all happen again.
This is a high expense all due to missing cylinders.
When ever anyone sees a flashing CEL lamp, stop. The above damage and expense can happen.
Good luck.

 

i have never had a CEL nor a flashing CEL. I had a miss fire code last year but i replaced the plugs and that went away. I dont have any miss fire codes now though.
It was night time when i looked underneath and seen the Cat starting to glow. So if you think its the Cat, would it run perfect when you crank it cold and then after about 2 minutes it starts missing?

 

Sure it's possible given you know what happened to the cat.
That bank may not be able to exhaust 'breath' from the high back pressure.
Look at the PCM with a Scanner on mode 6 and it will show you the missfire storage info for each cylinder.
Also look at the front and rear OX sensor switching rates for indication of cat damage. The rear cat sensors should have almost not movement.
If zero is seen, the PCM has suspended looking at them because there is no control value if they are not working and a code should be set.
If they are all on the same bank it a pretty good indication about the cat health.
This is no mistery if diagnosed properly using the right tools.
I don't know what you have but this is the way to look at it.
Good luck.

 

oh ok, yea i dont have a scanner like that. I am just using my SCT tuner (from my f250) to scan for codes. I wish i did have a good scanner, looks like i need to get one when i get some extra money.

 

When you crank from a cold soak the engine is running is open loop that is why it is running ok, as sone as it chanes to closed loop you start having the misfire. i would start by checking cats, and o2 sensors.