Hey guys. First off, sorry for the long post but I figured it's better to give all the details right off. I have a 96 f150 ext cab 4x4 with the 5.8l engine and E4OD tranny. I bought the truck with 125,000 miles a few months back. the truck now has 138,000 miles. Ever since I bought the truck I have had an acceleration problem/ hesitation you can say. The truck runs perfect at idle with just a slight miss. However, under a load, (driving) I have poor power (slow acceleration) almost the full length of the pedal. However, when I am almost to the end of the pedal, (right before it downshifts) there is a sweet spot. When I hit that specific spot, the power presents itself and bout pushes me back into the seat. I can repeat this even if I manually shift the truck. Each gear does the same thing. 1st, 2nd, 3rd, and so forth. I don't even bother to put the truck into overdrive anymore because it constantly downshifts. It has this problem on both tanks. I have absolutely no gas mileage. I replaced the fuel filter, which was disgusting. Replaced the plugs, wires, cap, and rotor button. I put a custom exhaust in and removed the second cat and gutted the first. Of course this threw a lean code and o2 sensor code. I bought a simulator which took care of my o2 sensor code. However I still had the bank 1 and 2 lean codes. I replaced all my vacuum lines because they were brittle. I check my fuel pressure which read fine at 32 idle and low 40s driving. (both tanks) it was a cheaper gauge keep in mind. I also pulled the vacuum line off of regulator and saw no fuel come out or any dampness. This whole problem pointed me in the direction of the TPS sensor so I replaced via napa part. Still no change. So I was told the Lower intake gasket might have an internal leak (because there was no change in engine tone when I sprayed starting fluid anywhere air could get through) so I replaced the intake gaskets and upper plenum gasket, followed by replacing EGR gasket and throttle body gasket. Also cleaned everything before replacing. While I had it apart I put a Motorcraft TPS sensor in. I also cleaned the injectors. After I got everything back together I cleared the codes and took it for a spin. The truck had so much more power for about 5 miles and started doing the same thing. I took the truck to several mechanics and the following has been replaced: ignition control module, ignition coil, distributer (including PIP sensor), another cap, rotor, and wires. I've gained a little more power but all that has done is pronounce the problem even more. They each have told me that they have no idea what's going on. I have my lean bank codes back on as well. I'm running out of options and its very irritating so if anyone has had this problem or something similar, any advice is greatly appreciated. Side note, my alternator puts out 14 volts when I check it but going down the road sometimes I watch the meter and it drops significantly. Thinking maybe the regulator inside is going bad but not completely sure if that would cause this problem.

 

 

Fuel trims were: bank 1 around 22 and bank 2 around 15 before I replaced intake gasket. After I replaced it: bank 1 was -3 and bank 2 was -1.

 

I had similar problems on a previous truck. I changed fuel injectors and turned the distributor by hand very small turn, problems went away.. fuel injectors I believe were the main cause.