Lower power after WOT under load

[mikeywrench]

My 2004 F-350 6.0 has low power after full load or close to full load. I. E. Pulling a hill or passing or heavy accel. When it has low power it sounds as if it has no manifold Pressure (Boost). until you put your foot back in it far enough to downshift and wind up above around 2750rpm. Truck also has very poor fuel economy. drove like grandpa for 3 tanks purposely driving economiclly and still had just under 13 mpg. Been to ford 3 times for this and still no luck getting tired of thier polish rebuild 3 days at a time. So far they have changed EGR valve and Exhaust Backpressure sensor. 25K miles on truck

 

[powerboatr]

welcome to the place
we got a monte sano mountain here in alabama to..
do you have any hissy noises like air escaping or weird phart whoopy cushion sounds.
do you have gauges?
how many miles
last airfiler change
oil change

 

[mikeywrench]

25K miles Yes it has the sound after letting of the throtlle. sound like a wastegate openeing and closing?

 

[mikeywrench]

Oil and filters changed every 5k with baldwin filters and delo 400 15-40 or 76 gaurdal 15-40

 

[powerboatr]

dropping the throttle whosh is normal its boost bleeding off through the vvt. a
gauge (boost) would help us here. to see if its boouncing or making correct amounts
any other maintenance recently

 

[mikeywrench]

no other maintinence.

 

[mikeywrench]

What is VVT?

 

[powerboatr]

vvt variable vane turbo
a neat addition to teh modern world
we use oil pressure to cahnge the angle of attack of vanes on the exhaust side of the turbo they are directed to open or close and controls teh amount of bost we get. a great thing we had in early versions was almost instant boost when we touch the throttle
but now in later programming to meet epa requirements they have changed the software to let the engine start turning up and then regulate boost then add fuel to limit black puffs and give us a cleaner enviroment. and qualify us an ULEV at least for 06 and some 05's

i am still curious as to info we dont have..
i assume you have no gauges
so lets start with the simply things first
air filter condition? clean, new or dirty
fuel filters changed when and what did they look like
to me and withoput knowing more i would lean towards a plugged or very dirty air filter

oh is the exhaust plugged or crimped some where, factory muffler is very restrictive, is it blue at the inlet from excessive heat?
do you have the catalytic converter still installed?

 

[mikeywrench]

no intake or exhaust restriction that is excessive. Problem is also interment doesent always do it then sometimes will do itjust cruising down the highway. but will almost always do it after WOT. No gauges yet. just purchased. I was leaning towards a VGT problem myself because after transmission downshifts and engine winds back up you hear it pulling boost and then have power again. Both fuel filters were clean when changed. No water in fuel water seperator which was suprising.

 

[powerboatr]

no intake or exhaust restriction that is excessive. Problem is also interment doesent always do it then sometimes will do itjust cruising down the highway. but will almost always do it after WOT. No gauges yet. just purchased. I was leaning towards a VGT problem myself because after transmission downshifts and engine winds back up you hear it pulling boost and then have power again. Both fuel filters were clean when changed. No water in fuel water seperator which was suprising.

as in pulling boost. do you mean you can hear teh turbine spinning up? or you hear a HISSSing noise.
Without gauges we could shooting in the barrel.
do you get a CEL check engine light? periodically ?
how long have you owned it and does it have a warranty remaining, may be worth a diagnostic run to see if anything is amiss.

you did check all the boots on the intercooler right, not just to see if the clamps are tight but physically pull on em to see if they POP off. or for evidence of Blow by, a nice clean area like what a high pressure stream of air would create?
sorry not to be of more help

could be one is letting off under driving conditions. this is a common and easy to fix deal.