Engine will start fine but begin to run rough once it reaches operating temp. Seems to stumble and lose power when you get on the accelerator hard. Then takes awhile to re-gain a smooth idle once you back down. Has had the fuel filter replaced already. Ideas? Thank you

 

What year 7.3?

 

2001, in and F-250. Sorry.

Could it bethe injector wiring under the valve cover? or the fuel pressure regulator valve? Justlooking for a general area to start

 

Ever any 'check engine light'.. How many miles on the clock?

Does it ever stall on/after a hard accell? It does 'completely' smooth after some idle time? even on a heated engine since you stated it runs roughonce it's at operating temp.. First off,, I'd check the fuel pressure for spec pressure 'AND' volume.. Possibly a failing fuel pump, but inside the fuel tank module there is not only a pickup screen, but the module body itself comes apart and inside are cylinder shaped micro screens.. They like to plug over time, or less than quality fuels used, and can restrict the fuel pressure/volume and can cause a flat throttle, stumble/misfire, stall, and can set DTC's.. Generally the performance will be poor at the higher fuel demands, but can stall or cause unstable low end conditions.. Could be a high pressure oil problems , or possibly bad injector orings causing a pressure bleed when the oil heats and thins.. Being that the perfomance dies off at high fuel demands, I'd check for good fuel supply first.. Then move on if it provesbe good.. UVC harness/s usually will set a code/CEL if bad/burned/corroded ect., or sometimes the holding clips will 'relax' over time and let the harness release and move out/off causing a misfire condition, but generally won't smooth as it has a chance to recover on an idle..

Can you simulate the stumble and loss of power reving it up in place, or power braking slightly? How long does it take under a hard accell. to get it to occur?

 

Have you ever had the fuel pump checked? I had a 02 that had a fuel pump that had good pressure but poor volume. It ran good at idle but under load it wasn't getting enough fuel.