My 86 F150 w/ fuel injection w/ 90K miles overnight developed this problem: when accellerating normally in especially 3rd and 4th gear (4 spd automatic) the engine hesitates and bucks. If I floor it it downshifts and will accelerate. Fuel pressure is about 35-40 psi at rail. Fuel filters replaced along with plugs and wires. I am thinking Bad Gas or would a temp sensor cause this problem. It starts OK when cold.

It has dual tanks and does it on both tanks. Not sure how well the valve actually switches tanks but the fuel gauge does change. I did add some gas to the front tank the night before this promblem arose.

 

***********Asking again*******

 

i had the same problem with mine, twice actually the first time i fought it for 3 months trying to figure it out. it would run perfect when it was cold then once it warmed up it felt like there was only 4 of 8 cylinders firing. a tune up (plugs, wires, C&R) and it was running fine the second time was when i ran it out of gas felt like the same problem i would do a complete tune up

 

Ok, so i completely overlooked where you put new plugs and wires on, Even though your fuel pressure is ok (asuming you checked it with engine off) mabey there is a clogged line somewhere where volume is the factor also check all injector connectors i had to replace almost all of the wiring to the injectors where the mice decided engine spagetti was on the menu.

 

id check timing too. it could have advanced slowy enough you didnt notice any change then finally its out so much that when it advances you having that problem

 

Does it do it at idle also? Mine did same thing it would kind of hesitate and "skip". I looked at plug wires and there was one sparkin to the block. So i replaced all wires and plugs. Fixed it and shes runnin fine. Also it musta been more than 1 cylinder on mine cause after the exhaust note was alot louder and not as muffled.