No real mystery. Your OEM plug wires are going bad and/or you have Bosch
plugs and aftermarket plug wires installed. If OEM they're 13 yeaes old.
These cars don't like Bosch plugs and eat aftermarket wires for lunch. A
failing coil pack is a possibility but it is more commonly the plugs or
wires.
=======
hi tom - thanks for the input, but here's the update...

OEM wires were replaced (with ford wires) and have less than 15,000
miles.  doesn't have bosch plugs,  went back the original brand.

the car runs flawlessly for that hour or so, and then the symptom
appears,  if problem were to happen with wires or plugs, it would
usually show up either when they are cold or somewhere during that first
hour of driving or under full load condition sometimes.   i don't even
have a hint of lack of performance during that first hour.

i've not had a coil pack go bad before, so i'm lost on that one.  my
question would be - doesn't a coil pack have one cylinder not firing
correctly?   when the symptom appears, it doesn't have a repeating dead
end, but a sputter type response, similar to a lack of fuel and then, it
might hit on all eight cylinders for a 1/2 mile or so, but the key to
the symptom seems to be that if you try to push the engine down the road
after the symptoms appear, the more you feel like you might be pushing
the car in another mile are so, because the symptoms, just keep getting
worse to where it has no power to pull itself, like up a hill.  for
example,  one event, i was traveling at 75 mph, but by the time, i was
at the top of the hill, it was down to 43 and that was not of cruise
control but feathering the throttle trying to get the every bit of power
i could out of the engine.  

i pulled off to the side of the road within a 1/2 mile of this event and
the running was purring like nothing was wrong.  put it in gear and call
for power and it feels like it wants to stall and will buck and snort.
turn the engine off, wait a few minutes and the engine runs great again
with lots of power.

~ curtis

knowledge is power - growing old is mandatory - growing wise is optional    
"Many more men die with prostate cancer than of it. Growing old is
invariably fatal. Prostate cancer is only sometimes so."
http://community.webtv.net/PALMER_ENT/doc

No codes even when it misses badly?  hmmmm.  15K on the plugs and wires
isn't exactly new. Im with Tom. Have you even looked at the wires,
pulled them out of those deep, water and gunk collector holes they're
in? Its amazing how a 4.6 can kill wires and plugs. Did you use the 32pp
plugs?(iirc) Start with the basics :)Someone mentioned a crank sensor.
I've seen them cause a no start but not a miss on a cv but you never
know....Try to get it to set a miss code....or some code :)

probably the easiest way to answer these responses is in one message....

======

From: gerald2003r@yahoo.com (gerald2003r)
Just a thought but you could have a faulty EGR or related plumbing.
Gerald
-------
hi gerald - had typical EGR problem long time ago.  fixed it, not had
problem since.  on related plumbing - all rubber tubing that collapses
for ford's poor design over time, (for example - the "t" connector and
the driver's side hose behind engine have all been replaced.
========

From: mush-hed@privacy.org (Shel-hed)
I only have guesses...
In old cars, this sounds like a pickup coil or ballast resistor. It also
sounds like the symptoms in my neighbors 91 bronco, his ignition module
died. It's mounted on his distributor, which gets hotter as the car
runs.

----------
hi shel-hed - on the 4.6L, it doesn't have a distributor, or ballast
resistor -  so that rules out the common problem that ford had on what
you described.  but that would have been one of the things i would have
jumped on had the engine had a distributor.

==========
From: pettyfog@yaywho.com (Backyard Mechanic)
Have the codes read out.   Then come back with them. Codes, not
definitions

hi backyard - no codes are coming out - that's the problem.  that's the
head scratcher......

Here's another thought:
1. Get a can of 'circuit cooler', locate all suspect modules, then when
it happens.. spray them (heat sink not the plastic) and see what one
affects and what one doesnt
-----> i hadn't done that yet and had gave it some thought, but i will
probably have to carry it in the car and perform road side
troubleshooting when this happens.  was hoping that someone had ran into
this problem from the symptoms i was describing.

2. When it happens, go back and vent the gas tank.. tighten it back and
try immediately

------> tried that the first, second, and third time it happened.  made
no difference.

thanks for all the input so far.  i really do appreciate it.  

i've had some real hair pullers in my time and they usually end up one
of two ways.  
1.  the "wow!" i could have had a V-8.  so simple and it's one of those
slam yourself on the forehead type solutions.

2.  the bastard case.   you happen to just catch it at the right time
and were standing at the right place.  any other time, it doesn't show
up.

~ curtis

knowledge is power - growing old is mandatory - growing wise is optional    
"Many more men die with prostate cancer than of it. Growing old is
invariably fatal. Prostate cancer is only sometimes so."
http://community.webtv.net/PALMER_ENT/doc

bob wrote - If you haven't replaced the fuel filter lately do it now and
let us know what happens.

---------> fuel pump and filter both replaced about six months ago.  

before fuel pump and filter were replaced - the engine did have one
episode similar to what i'm describing about 9 months after about 2
hours of interstate driving, but i was close to home when it was acting
up   and was going to work on it later that day but problem went away,
so didn't give much thought.  now, it seems to be back and a lot more
frequently, and with a new pump and filter in place.

========
From: pettyfog@yaywho.com (Backyard Mechanic)
PALMER_ENT@webtv.net (c palmer) wrote:
    at first, one will think it is the fuel system, but this has
been ruled out already.

IOW, you are saying you KNOW you have proper fuel pressure AT THE TIME
the Engine is running badly.
Hate to be a poopy-head.... but you DONT call a consultant into your
business to solve a problem and tell him the obvious has been ruled out
without reviewing it.

-------> don't worry about being a poopy -head, i'll take any ideas and
leads.  :))

you are right, i didn't have a fuel gauge with me at the time it was
acting up.  but, what puts a spin on this problem is that i have been
able to put it in neutral, kill the engine and coast almost a mile on a
down grade. (thinking that the passing air would cool down the part or
module)  when the speed drops down to where traffic is passing me, i can
start the engine and it runs great.  have even taken on the next steep
hill under full throttle delivery figuring that if it is a fuel delivery
problem, holding the engine's feet to the fire for a longer duration
than what one takes to pass, should show up something  - if it was fuel
related, but the engine hung in there and kept delivering the power with
no miss or stubble.

=============

From: gerald2003r@yahoo.com (gerald2003r)

Is vapor lock unheard of in fuel injected engines?

------->i, personally, haven't heard of a fuel injected engine vapor
locking.
=======

If it were me I would go for the coil pack, BUT before I did that I
would disconnect the battery for 10 minutes or so to lose anything
stored in the computer. Maybe look at the coil pack electrical feed
connections? I don't know the design of the coil pack enough and it
would be interesting if someone here could speak about it to say if the
1993 series coil packs are one as a unit of if they will fail separately
per cylinder? When it comes to engine management I think computer...
Disconect that Battery and see what happens first... The computer is
also going to tell the injectors when to fire. I understand the heat
failure idea but I'm thinking the computer forgot what to do idea is
also plausible. Worth a shot...

==========

-------> the coil pack design are four to a side - up front.  they don't
get the heat as they would if they were installed on the back side of
the engine or in the case of the 1998 and up with the coil over plug
design, where heat is a common problem in killing the module.

the check engine light does comes on, but it is a soft core error, and
the computer resets itself,  when the key is turned off.

i haven't been able to get to anywhere to pull the codes when the check
engine light comes on.  just seems that i'm at the wrong place at that
particular time.   along with the can of "quick kool", i should bring my
x-ray hook up unit too.

---------
From: newton5@remove.comcast.net (Tom Adkins)

    With the extra info, Yep, that's a head scratcher. That hour
of good performance throws me. There's 2 things that come to mind for
your symptoms, but they don't seem the fit the conditions that you
describe exactly. First, pull the plug wires and apply a liberal amount
of dielectric grease to the boots then drive it to see if there is any
change. Then, clean the element on the MAF sensor with a non residual
solvent, see if that changes anything. Obviously check the fuel pressure
when the symptoms occur, but I wouldn't expect to see a large drop in
fuel economy if the engine is not getting enough fuel to start with.
    I recall hearing something about flaky Crank Position Sensor
connections being common on these motors but I don't remember the
details.

============

--------> anything is possible when it comes to mechanics, that's for
sure.  but the plug wires are fairly new.  i just pulled them after i
read your post and the boots are still good and soft, with no evidence
of carbon tracking.

the reason i replaced them was because it did have a repeated misfiring
(common for plugs and wires) and it did fix the problem right away and
it was permanent.

with the MAF sensor, i don't think would keep resetting itself.  by
that, i'm referring to where the engine, goes right back up to the 23 -
25 mpg range after the problem resolves itself.  that is, until, the
symptoms show it and then, the computer's overall mileage - after reset
- will show 12 - 13 mpg while the engine is acting up.

i'm not aware of how the flaky crankshaft sensors are suppose to behave
when they are going out.   unless my thinking is off, i'm thinking that
when the engine doesn't get the crankshaft sensor input, it just doesn't
fire.  this engine fires, but sputters-like and i have to keep in mind
that it still idles great when these symptoms are going on, just can't
call for power from the engine when it is in this state.   another head
scratcher.

---------------
maybe, i'm just getting too old for this stuff and they can just hook it
up to another computer and let the two computers talk to each other.  i
know in time, the part will fail and then it's easy to find, but i don't
want to be miles from home.  wife has had two heart attacks, plus two
partly stopped up stents and i've got two different cancers chewing on
me and bum knees.  so neither one of us don't need be walking on the
interstate, especially, if you know that something is not quite right
under the hood.   i use the car a lot to go the VA hospital in the next
state over for treatments and follow up visits.  that might explain why
a lot of interstate driving.

~ curtis

knowledge is power - growing old is mandatory - growing wise is optional    
"Many more men die with prostate cancer than of it. Growing old is
invariably fatal. Prostate cancer is only sometimes so."
http://community.webtv.net/PALMER_ENT/doc

look to see if the last person to do an oil change missed the fill hole in
the valve cover and dumped oil down the intake. if he did, the oil will fill
the plug holes, and short out the wires, causing a noncode  miss on
acceleration.  i have seen this 3 times now.

That reference to CC keeps coming up .  Had a problem with my 95 taurus
about 3 years ago, where it seemed to fall on it's face for about half a
second just after I switch CC on; then recovered and worked okay.

Next trip, it ran fine till I switched CC on... few seconds later it died
completely and wouldnt restart till a few minutes went by.
I avoided switching on CC again till I replaced the servo unit.  Havent had
that  problem since.

Dunno if that's your problem but sounds a little similar.  Note the effect
lingered after key was off-then on. a headscratcher.

 This is true... but, the 4.6 doesn't have an ignition module per se. The ignition is
controlled by the PCM. It could be the problem but that would be the first time I've
seen or heard of it on one of these cars.
 Curtis, If you have definately ruled out the ignition system, move on to the fuel
pressure. Use a gauge with a long hose taped to the outside of the windshield.

Good idea!

Gerald