F150 gas engine help

[powerboatr]

Well the ford folks are useless so i am asking the brains here

in february our f150 died on the road and we had to be towed to a real nice ford dealer for repairs.
they changed out a fuel vapor vent valve , that resides at the rear of the intake manifold and is responsible for purging fuel vapors as you drive. this was at 48k miles

prior to its failure we were getting 17.3- 17.8 mpg at 70 ish
this is a 5.4 engine, 3.55 rear end, michellin ltx2 tires 52k on the odo

now we are getting 14.8 - 15.9

first tank i figured it was because we had bad gas and winter blend crap

subsequent tanks, over 10 we have used 92 octane, and every blend in between, plus ethanol removing additives
lucas, chevron tech, etc

but fuel mileage is still horrible, but power is still super just like before.

I have removed all intake plumbing and checked for blockages
new air-filter
i removed all the exhaust and inspected it for blockages
the interior of the exhaust is sooty, like its running rich, but not liquidity, just dry medium soot feeling

i thought the cats were blocked from the raw fuel that poured from the tailpipe at the ford place once they got it to start
but i have run temp sampling after a brisk drive and both cats are running 340-380F on several runs, muffler inlet is 190- 210F
i pulled the muffler and eyeballed the exit and inlet and saw no blockages, but didn't do an airflow test yet

i first thought maybe the ecm thought the truck was new and was running a richer program until break-in is reached....why you ask
the ecm fuses were pulled and the all 12 volt power was off the truck overnight at the ford place.
my dealer at home is clueless, and can find no codes or irregularities
sooooo
where do I go now
trade it off

 

[f100cleveland]

Ford is good at having the dealerships reflash trucks in for any service work with their latest and greatest PCM flashes. Happened to mine and lost mpg. Could of happened to yours.

 

[KRISTOLSON]

Maybe the O2 sensors could be fouled from all the fuel and soot?

 

[powerboatr]

I had my ford guy pull the RO ticket and no reflash was scored
I also took out the maf sensor and gently cleaned the shiny slick air ramp parts, it was less than clean, but not gunky
went for a drive........wholly ****ii

barley touched the throttle and spun the tires, well jammed it like i have been the last month
drove two runs back to back 6 miles, not very long..one was into the 12mph wind at 70mph cruise
mpg climbed up to 18.2, then stabilized at 17.8
return with a 12 mph tail wind i attained 70 in a quick manner and she dropped to 15 then climbed back up in 2 miles to 18.5
then drove at 60 for 3 more miles and it moved up reading to 19.3
sooooooo
going for a long drive on friday
mind you the lie o meter is pretty accurate.
no way to fill and add with the capless neck.
i was looking at new maf sensors, and stumbled upon a tip to clean the shiny parts?

 

[Dogman]

My 6.0 maf would get crap on it and the mileage would tank. I always clean the maf at every oil change. Does not take but a min. on the 6.0 motors. One thing I was always told is if air can pass by it's going to get dirty.

 

[Dieselpwrdredneck]

wow thats good info,my girlfriends truck is gettinfg about 15.3 mpg now, im gunna have to try that might go do it tonite, takin it on a 2.5 hr drive tomarrow

 

[f100cleveland]

Sounds like you found the problem. What did you use to clean it?

 

[powerboatr]

Sounds like you found the problem. What did you use to clean it?

a long soft industrial q-tip dipped in iso alcohol. very gently rubbed the shiny spots, i mean GENTLY
still not sure why the shiny stuff needed to be so clean, as the air simply speeds past and up into the ramp to the detector???
we shall see

i also read the air temp sensor if dirty will read a COLD to the ecm thus creating a rich run ?

 

[JLDickmon]

Umm... CRC makes a MAF cleaner...

 

[Dieselpwrdredneck]

Umm... CRC makes a MAF cleaner...

Got some and tried it friday nite, i suppose if you had oil that needed cleaned off it would work great, but i couldn't tell it doing much good. did the cleaning and installed a new air filter and still the BEST i could get was 15.8 mpg highway