Here I am once again dang it. I have a 92 f150 4.9, aut. with od. When i got it it had 80,000 miles, it got 17 mpg on HWY. I was satisfied bud not happy. A year later it stalled out anywhere and anytime. I read codes, none showed up. I checked the fuel filter and it was plugged VERY tight.Replaced it and prob solved,,,,BUT hard to believe but i am now getting 22-23 mpg on hwy with ac on. Checked it over and over and still 22-23 mpg for 1500 miles. Even my wife drove it and she checked mpg,got 22-23 mpg. Tickled pink I was. !500 miles later the same prob, started stalling on HWY at 50 mph or 75 mph it would die out and stop.It may start back up in 1 minute or it may take 5-6 hours to restart,it would run excelet till next time.If you let it set for 1 min. it would run for 1-2 minutes, let it set 20 minutes and it would run 20-45 minutes then stall. When the evenings were cool it may run 1 hour or more before dieing..checked a few things and had auto parts check allso and had to replace the ,map,oxygen sensor.Coil and wire,control mod to.and muffler.Runs ok but loafs a little.Put a plat at the egr with 1/8 hole.I am getting 14 mpg now.I know it will get over 20 mpg as it did before. PLEASE HELP

 

Forgot but allso relaced the air filter and plugs. Checked the tps and it fine. Fuel pressure is right on with engine running and koeo. Allso replaced the fuel pump. Checked the release valve thing on fueline and its good to. Thanks Come on now i know you guys and gals are good,you allways helped before, lets put our thinking caps on,lol.

 

just a thought....the ford pickups use multiple pumps(whatever the hell for)...there is one in the tank(s) and one on the frame...low pressure in tank, high pressure in frame....could be the pump you didnt replace. if it does it on both tanks you may be lookin at the high pressure pump goin out. but good luck and hope some others can shed some light too.
mike

 

ok- you said that you were getting @ 17 mpg, then the filter plugged up- changing that got you @ 23 mpg- this tells me that the filter was restricting the fuel pump. not enough fuel means more throttle pedal equals lower milage. the first place i would look is the fuel filter again. if the filter plugged once, theres more mud in the system. pull the filter out, retain as much fuel in the filter as possible, and whack the filter against the floor- this will dislodge the dirt in the filter. hold the INLET end down and see what comes out. what happens is as your driving, your stirring up all that mud in the filter. as the fuel passes thru, it catches the mud and holds it against the filter. eventually you can choke the filter off and the motor dies. now for the fun part-letting the car sit allows the mud to fall off of the filter media and to the bottom of the filter-now the %$&@# truck starts! lots of true 'automotive gurus' get spanked by this on a regular basis! one other thing- expect to have to change both the fuel pumps. usually, iif the pumps have been laboring against a plugged filter, they will overheat-this beats them up . another area to look at because of this is the electrical system for the pumps-the higher load on the pumps overheats the electrical system for the pumps-check for a relay in the electrical system, as a cooked relay can malfunction intermittently, causing your type of trouble too. check fuel pressure at speed-sometimes a fuel pump will deliver enough pressure at idle, but it will fall off of pressure as engine speed and load increases. and remember, all that mud in the filter allready passed through the pumps' impellers! last thing to look at is the fuel tanks themeselves- if you have mud and such rolling around the bottom of the fuel tanks, it may be choking off the in-tank fuel pump, especially if the pump has an inlet sock- like sucking a milkshake thru a straw! oh, by the way, the in-tank pump is the lift or supply pump, and the other pump is the pressure pump. anyways, hope this helps-sorry for the long post!-dave-

 

Not really - the injectors just stay open a little longer on each pulse. You don't notice it, and you don't have to change the throttle position.

'90-up doesn't have the frame pump - he only has in-tank hi-pressure pumps.

 

Thanks for the input guys. Forgot to say but I replaced the filter again (however the old one was not clogged)Anyway it has a new filter and while putting the pump in, I cleaned the tank, like new now.And yes thats right I only have the one pump. Any more Ideas would be app. Thanks,,