2005 5.4L F250 loss of power and moaning on acceleration
 

I'm new to this, so please forgive me for any etiquette issues. I have been struggling with this problem for four years now and am finally getting around to posting it online to try and get some help. I have a 2005 F250 crew cab with the 5.4L Triton engine. Let me tell you what it does and then what I've already done to try and fix it.

When I accelerate relatively lightly, especially after the engine is warm, and usually in warm weather, and when the engine is under load (i.e., the AC is on), the engine loses power and moans for a few seconds until it can regain its composure. It does do it in cold weather but not until it has warmed up. It's almost immediate in hot weather. It usually only happens when shifting from first to second gear, and sometimes from second to third. I now have the P0171 and P0174 codes.

I have searched incessantly online about this and have already tried most of the things I've found. I discovered the trick about weather stripping on the bottom of the air filter carrier. Mine was once gone, but I've gone to great lengths to try and seal it up including screwing the carrier into the air filter box. Usually it fixes the problem for a short time (i.e., maybe a few days) and then the problem comes back again. I've even gone so far as to buy a brand new air box to make sure that there wasn't some crazy leak in it somewhere to no avail. The new one at least has the stock foam on it so I have to think that it's how it should be.

I have replace the MAF twice. That helped initially while the fuel trim readjusted itself, but comes back. I have replaced the fuel filter which also helped initially because it was quite dirty, but the problem resurfaced. I have replaced the throttle position sensor and cleaned the throttle body. I've sprayed the engine with carb cleaner looking for vacuum leaks but didn't find any. I've done the throttle calibration trick with turning the key to "on" and pushing the gas pedal down.

I feel like there's something I'm missing, but at this point the only thing I've read about online and not tried is having Ford flash the PCM. It seems to me that if there was a fuel pump or pressure problem, I'd have an issue at high RPMs too, and that's not the case. It only happens on light acceleration under load. It also seems to me that if there was a vacuum leak or other physical issue, that it wouldn't run well after I reset the computer (i.e., remove power from it for a while), but it does temporarily fix the problem. The problem only comes back after driving it for a few days after the computer is reset.

I should mention that this engine was replaced under warranty by a previous owner at around 115k miles due to the notorious cam phaser problem. Don't ask me how he got Ford to agree to that, but that's what the paperwork shows. The truck has around 176k miles on it now.

Any thoughts or suggestions are greatly appreciated.

I would replace the PCV valve since it's cheap. Then I would replace the O2 sensors if they're original, or test them to make sure they're working. Are you running motorcraft spark plugs?

Thanks for the reply and ideas. I should have mentioned it in my original post, but I replaced all of the spark plugs around 25k miles ago with OEM Ford plugs. Thankfully I didn't have any problems getting the old ones out and they looked decent. I'm guessing that they were probably during the engine replacement.

I thought about the PCV valve too, but everything I can find (and even looking around the engine) says that it's built into the valve covers and isn't replaceable. Maybe it's worth cleaning either end of the PCV tube out with some carb cleaner.

I haven't checked the O2 sensors but that might be worth a shot. I just figured that I'd get a code if one failed, but I guess there could be some minor problem that's causing issues that isn't throwing a code.

I'll check on this stuff and report back.

fix?
 

Hey did you ever get it fixed mine is doing the exact same thing

Fan clutch is sticking, try it, bet you will be all fixed.

Unbelievably, I replaced the fan clutch and that fixed the problem. Thanks much for the suggestion because I wouldn't have ever thought of that. Now I just need to decide if I want to keep the "severe duty" clutch that came from the local auto parts store on there (local stores only sell "severe duty" versions apparently, but the fan spinning harder definitely makes it louder than the stock clutch) or find a quieter standard duty one. This takes me down a completely new rabbit hole of research trying to figure out how much power the SD clutch is costing me, but I'm just happy that my hesitation is gone!

Glad it worked, been down that road before, the SD is a good one to keep on there, doesnt cost you much power really.

So I'm sad to report that after some time, the hesitation issue is back. I don't know why this engine/computer setup is so bent on giving me problems, but I can't tell you how many "fixes" I've done that have improved things for a week and then eventually returned to the "bad" state. It was like that when I replace the fuel filter the first time- it ran excellent for five or six days, and then back to moaning and hesitation. Same with new MAF sensor. Same with new fuel pump. Same with the fan clutch. It was even the same when I replaced the CVT solenoids, which aren't seemingly related to fuel and/or air at all. All I know is that the problem seems to be related to the engine getting too much air for one reason or another. I can't shake the "Bank 1 and Bank 2 lean" codes and check engine light now at all, especially when it's hot outside. Both banks always come on simultaneously so I have to think it's upstream of the throttle. I do know that when I mess with the seal between the filter carrier and the filter tray things can change pretty drastically. It'll run quite well (albeit not perfectly) if I seal the filter tray up tight but'll bog down if there's any air leakage around the bottom of the filter tray at all. This might actually be another symptom (rather than the actual cause), but I keep thinking it'll eventually lead me to the problem.

Any possibility someone put a bad tune on this before I got it and that's causing it to gulp more air than it normally would from a stock tune? I keep thinking that I should maybe take it to Ford to get flashed but don't want to spend the money if it's not a possibility.

So for now, the long, long investigation continues.

Try plugging a good scanner with live streaming data in.(I use a actron scanner but there are other good ones) and watch what is happening as you drive down the road from cold to hot it may give you some insight iinto what is going on.

You may want to pull the IAC "idle air control" off and give it a good cleaning. They are notorious for causing all kinds of issues. I had a 01 F150 with the 5.4 for 7 years. I had to pull the IAC and clean it every couple of years.