To start, 2004 F150 Supercrew 2WD 5.4, 175000 miles...I got this truck about a year ago and was not expecting a tire burning monster, but I feel like I should be able to merge onto the highway without worrying about getting smashed by traffic. Essentially, this thing cannot get out of its own way at WOT, or part throttle for that matter. MPGs have declined from about 12 to 9.5 over a year.

I have cleaned the top end, throttle body, MAF (recently just replaced), replaced plugs/coil packs, cleaned injectors, replaced fuel filter and FPDM, tested vacuum, and resealed the air filter tray. I'm about to do my next oil change and will be doing trans fluid with filter as well.

I've been scouring these pages and have found similar fixes for my acceleration issues, but nothing has worked out quite yet. After paying closer attention I have discovered a very specific point during operation that my truck begins to develop poor acceleration throughout RPM/Shift ranges.

Acceleration is pretty normal from cold start until normal operating temps...once the temp gauge reads halfway, part throttle and WOT make the noise, but have no go. The truck begins odd shifting patterns (won't downshift, or shifts earlier than expected). I do not have access to a live data stream at this time, and my code reader only displays basic monitors (and no codes).

I was just trying to see if anyone else has experienced this and if I may be missing something.

Thank you.

 

That’s horrible mileage.

is it lifted?

Are wheels stock?

what size tires?

if not stock size, had pcm been adjusted for them?

what oil ?

have you ever checked oil pressure, hot and cold?

 

It's got a 1.5 to 2" level kit, 20" wheels (I can't remember the tire size right now, but they measure about 2" total taller than OEM).

These came with the truck so I have no idea if the computer has been flashed for the size, that was going to be a future purchase.

I use the standard 5w-20 synthetic and motorcraft oil filter.

I have not checked oil pressure other than what factory gauge displays, but I can add that to the list.

Another thing I forgot to mention, the truck is totally stock other than the wheels and tires...except for the exhaust. The previous owner chopped the exhaust at the end of the y-pipe and welded on a pipe the dumps to the ground...another thing I was going to replace. I have noticed quite a bit of black soot at the pipe which leads me to believe it's been running rich.

 

Lots of stuff working against you by the sounds of it.

the wheels/tires/lift are hurting. Uncorrected odometer for tires make it seem/calculate even worse than it actually is. Cant be helping your acceleration issues either.

too bad exhaust is hacked

oil is semi controversial, but the consensus among the people I choose to trust/listen to is that it’s much better to run 5w30.

 

Unfortunately I like the way the wheels/tires/lift looks...I have been thinking about either getting a tuner or finding a tire size closer to OEM height. I used to work for Toyota and I remember the second gen Tundra's would throw a fit if the tires were even just slightly taller than stock.

I'll be re-doing the exhaust completely once I get a chance.

 

wonder what gears you are up against.

 

For comparison, my 2005 5.4 4X4 has 2.5" Rough Country level in the front and a 3" shackle lift in the rear to restore the factory rake. I'm running 35X20" tires and just upgraded from the factory 373 gears to 456. I get about 14-15 mpg hwy and 13 city. I know yours is 2WD, but wanted to give you a bit of a reference.

 

not bad. Is that hand calculated? And was it reprogrammed after new gears and tires ?

 

Hand calculated using 5 different sets of data a week apart each and using the median. Also updated for gears and tires using Edge Evo. I'm still 3% slower than GPS reports at 100 km/h so I might mess with tire size a bit more. But 3% isn't bad.

 

At first I was going to say maybe your cats are clogged, but I think that would exhibit all the time, not just after warmed up.

Perhaps you have a brake that starts dragging after driving around for a certain amount of time, or is it related to engine temperature only? For example if you let it warm up by idling until at temp is the issue immediate, it does it happen after 5 minutes of driving down the road?