My 2003 V10 Excursion is surging under hard acceleration. I don't usually drive it hard so there's no telling how long it has had this issue. It starts easily, runs smooth, and drives just fine under normal conditions which is me never pressing the gas more than about 60%. I've Googled this issue and searched it here. Evidently there are a lot of people who have problems with their Ford V10 surging at idle/low rpm but not many of us having the issue at full throttle. I noticed it a couple of months ago when I had to pull out into traffic on a busy 4 lane and was trying not to be that guy who everyone hates because he pulls out in front of you and doesn't freaking go. Oddly, I have not noticed any surge or other bad manners when pulling my 10.5k camper in the N Ga mountains. It'll sit there smooth as can be at 4000 rpm on a steep hill and pull like an old John Deere.
What I've done since finding the issue...I secured the MAF plug in the bottom of the air filter housing with a bungee cord. Mine tends to fall out. Cleaned the MAF with a can of MAF cleaner from AutoZone. It's had plugs and boots in the last 20k miles. FWIW, this doesn't feel like an ignition miss although I suppose it could be. It does skip and chug for a couple of days after a heavy rain because I haven't fixed that stupid hood gasket yet and the COP's get wet. They always dry out though. New air filter. No codes...pending or stored. I'm running a 5 Star 87 octane performance tune. I did replace the fuel pump with a Delphi from Autozone a while back and I thought maybe that was the issue...or the pressure regulator. Today I attached a fuel pressure gauge and drove it. Pressure never drops below 30 psi and goes immediately to 40 psi under hard acceleration so, even though it's not a Motocraft pump, I don't see that being the issue. I also replaced the fuel filter since I got a double handful of sand out of the gas tank when I installed the new pump. WTH? My long term fuel trim stays in the .95 to 1.01 range all the time on both banks. Seems like if I had a bad air leak, I'd see bad numbers there as the engine computer tried to compensate. This truck has almost 299,000 miles on it. Could it be worn out injectors? I did not see a drop in fuel pressure after shutting the engine off so I don't think any of them are leaking down. I'm open to ideas at this point.
Truck specs are as follows: 2003 Ex Limited, 6.8, 4.88 gears, 33" tires, Livewire with 5 Star tunes.

 

sounds like fuel starvation, fuel pump cant keep up at wide open high RPM, its probably just a bit weak, and only has trouble at peak, ive seen this before im my mustangs.

4000 RPM part throttle is not the same fuel demand as lower RPM but wide open, put a fuel pressure gauge on and go do some WOT pulls, i get you see the pressure bounce with the surge.

EDIT: somehow my eyes skipped the pressure gauge line of your post, i just re-read and this time saw it, but it does sound like a fuel issue. Unless its slipping in the TC or Trans, which makes it feel like a surge.

 

It feels like a fuel issue. If it was an older carbureted engine, I'd be looking at fuel pump and float levels. I did a couple of full throttle from a dead stop runs yesterday, and the fuel pressure gauge stayed on 40 psi...never faltered. That's why I was wondering about the injectors. Is it possible for them to cause this? I did not observe any leak down after I shut the engine off although I only left the gauge on for about 5 minutes after which I managed to spray gas all over myself letting the pressure off the stupid gauge
Trans slipping is not something I'd thought about. Wouldn't rpm increase slightly when it was slipping? I'm seeing a slight drop in rpm on the Livewire when this happens. It also doesn't do it on a hard pull in the mountains. It's really only when it's at probably 90% or better throttle.
I don't want to start throwing parts at it but I'm almost at that point.

 

When I am that tempted to just throw parts at it, that's when it's time to spend the hundo on an hour of diagnostic time at a good shop.

 

Sounds stupid but have you tried running a can or two of Seafoam through it?

I had a miss in my cop car. Replaced the plug, cop and injector in the offending cylinder (#2), no joy. This is really stupid... Happened to leave the hood open in the sun... Next time I drove it, no issues. Crazy.

 

A can of Seafoam or especially BG44k should be part of regular maintenance.

 

Well...I would have bet my next paycheck that the hard acceleration surge was a fuel starvation issue. I would have lost. Since the original post, it developed a miss that I could tell was ignition. The heavier the engine load, the more pronounced the miss was. It never stored a code. By now I'm frustrated with the whole thing so I replaced all 10 cops. Miss is gone. Surge is gone. It pulls smoothly all the way to the WOT shift point. So my V-8 3/4 is back to being a V-10 again. I will try the Seafoam as well...can't hurt. I don't see how these injectors are still working correctly after 299000 miles although I don't know that they weren't replaced by a previous owner. I guess if it ain't broke, don't fix it.

 

Great news that you got it fixed. In your case I don't disagree with you replacing all the COPs, since it gives you a maintenance baseline for those items. Does your Livewire give you the ability to live monitor for misfires at each cylinder? That could help you diagnose in the future while driving around. I've done that with my set-up, but I don't have the Livewire.