My 2000 V10 Excursion misses under load. It has done it for a year, since I got it. Climbing a hill with a trailer is when I first noticed it, when the tranny downshifts so the rpm goes up, under full throttle. Feels like it is runing out of gas. I have 36 tires on it, it had stock hearing then. I regeared it, now the problem is much more pronounced, probably because the rpms are higher when the trrans downshifts under load. It was so bad that coming back last trip, the truck got weaker and weaker until it wouldn't go 35mph on the level road. I pulled it off, it was missing like crazy when I hit the gas in neutral, but idled great. I shut it off, popped the hood, couldn't see anything obvious. For grins, I started it back up and it was fine. Problem gone. 10 miles later, it started doing it again, gradually worse until undriveable. Pulled over, shut it off for 3 seconds, started up and fine again. I did this three or 4 times to get home, shut it off, restart, problem gone.
What I noticed is that on the straight roads, it wasn't as bad. In the twisty mountains it happened quicker. The other thing that changed between road trips where I notice it is that I put a lot of questionable gas in it. Gas I pulled out of old watercraft I was parting out, smelled fine but I noticed that some of it was cloudy after I had poured a bunch in.
My thoughts were that my tank is full of crap, the truck has 207K on it. It acts like the fuel filter or pump pickup gets clogged, as soon as I shut off the truck the crap falls back off the pickup and it runs fine until it collects again. That would explain why turns and sloshing make it worse.
Buddy told me today that his used to do that, sort of similar, it was coil packs than weren't throwing codes but causing misfires. Seems to me that if that were the case, it wouldn't get worse and worse like it does, but I don't know. I have a new filter for it, was going to drop the tank to clean it and look around a bit, but anyone have any ideas?
Chris

 

Start with the bad gas. Remove tank and clean the tank out. Put fresh gas in and change the fuel filter

 

Yah, it is on the list. Installing a x-over steering knuckle now. I was pretty confident that it was the problem, until my buddy said it sounded like coils.

 

Find someone with a DTC reader that reads pending codes. If that states a misfire then i could lean towards bad coils.

When i first got my V10 i had a very rough idle and a slight hesitation in the pedal. And sometimes the truck would stall when put in reverse. I cleaned the throttle body, MAF, and
replaced the fuel filter. Made a total difference! Start with the cheap repair first, and work your way up

 

Yah, that is how buddy found his problem, drove it with a code reader attached. I don't think the cheapy one I have will read codes unless they are actually thrown, as in check engine light?
Mine idles great, great throttle response. A VERY slight occasional rough idle, but I attribute that to the fact that the plugs have probably never been changed, and I am not about to risk doing it, lol.
Spent all day on that crossover steering knuckle and making a steering rod and welding a custom track bar mount on the axle. Hopefully get it going tomorrow and look at fuel issues after.

 

also check the pcv hose under throttle body, these sometimes split and create vacuum leak.

 

I used Torque Pro and monitored for misfires, they never showed in report. Purchased 2 coils, all new plugs and boots. Replaces 2 coils at a time starting with #1&2. Finally got to #9&10 and the misfire went away. Swapped out the coils 1 at a time till the misfire came back and found the bad coil. It went in the trash and the other coil is now a spare. At almost 150k miles, some of the plugs I pulled were worn to a .090 gap.

 

I hope after 8 years he has found and fixed the problem

 

Yea, it pays to do a little research before replying to some threads, like I did not do. :-)