We have a 2004 F350 Powerstroke, 6 liter engine with 126,000 miles. We haul trailers, 5th wheels and travel trailers, all over the country, some as heavy as 19,000 lbs.
Recently we started having an issue of loss of power while hauling the heavy trailers. We will be motoring along just fine, then any slight incline and the speed will drop from 65 down to 35 and not go back up unless we go down hill or pull off the highway. We can get right back on, speed is back to normal, then drops down to nothing again!
We have changed both fuel filters. Now while NOT pulling, you can feel the truck 'chug' even at 60 mph. We don't get a loss of power like we do when pulling, but it starts to chug a bit almost like it's not getting enough fuel.
Any insights before taking it in would be greatly appreciated!!

 

What fuel filtets are you using? 6.0 are real picky about filter brands. I think these guys reccomend ford or Baldwin

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Got them at O'Reilly's....I think they were Fram but not sure

 

Well may not be whole issue but id go get some motorcraft filters. Do you have access to a good scanner? not the ones at oreilys. One that can read icp, ipr, etc and buzz test your injectors. Anything done to It? Chip, gauges, deletes? Etc.

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Our mechanic scanned it with a scanner from the Ford dealer and told us that 1 injector was bad but not bad enough to replace just yet since it seems to work fine after it warms up. Had a code come up for a bad gas pedal, replaced it but nothing changed.

Could the fuel pump be acting up? Or fuel pressure?

 

Sounds like it. Do you know if he tested FICM?

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Not sure...I don't even know what FICM is! LOL

 

Wouldn't hurt to test fuel pressure, but I doubt it's your issue.

What mods are done to the truck? Stock?

Has the EGR valve ever been pulled and cleaned? I'm sure if it's stock with no mods it needs to be done. An EGR delete would be even better for you.

 

It's stock and the EGR valve is disconnected.

Any other ideas?

 

Yeah, disconnecting the EGR valve doesn't fix it, it can still blow open. Pull it out and check it. If it's partially stuck it would kill your power pretty good.

Check fuel pressure anyways.

Like 1999stroker said, have your mechanic hook his "scanner" back up and monitor ICP actual vs ICP desired, and check IPR % duty cycle too. Let us know what it's doing. You should ideally do this at idle and while driving. ICP should go up to 4000psi ideally, both actual and desired, they should be very close to each other. If desired goes up to 4000psi under WOT, and actual is not, there's a leak in the high pressure oil system.

Has the FICM been tested??? Test procedure at the top of the page in the 6.0 section...