96 F150 4.9 5speed 2wd

I've been having this problem with my truck for a couple months. So it seems to happen more when it's hot out. I step on the gas and it barely moves feels like I'm driving a semi-truck!! 1st gear..... 2nd.... 3rd... Finally starts to actually go... Now heres the catch! If I'm at a red light, I'll turn off the truck. Once its green ill start it up! And it goes like she was a brand new truck off the lot!! Then couple miles down she'll go back to the problem.. Now usually at night, weather cools down a bit and SOMETIMES she'll run fine. But you can seriously tell the difference! Help guys! Could it be a bad sensor? Fuel problem? Anything is helpful.

 

xBUMPx

Update:
So I've changed a few things on this truck trying to figure out why it's so sluggish.
TPS
ICM
ACT
Ignition Coil
Plugs .46
Plug wires
Cap n Rotor
So far.. Still the same problem. But at least all these parts are new, right? Well finally I checked my fuel pressure on the rail. At idle it was reading at 45psi. And if I gave it gas it would jump to 49/50psi and back down to 45psi. What pressure should I be getting on my 96 4.9 I6??

 

Just dealt with some of this myself recently. 4.9 needs 50-60 psi, so you're low. Change the fuel filter if you haven't. If that doesn't help, I'd check the fuel pressure regulator next. After that... Fuel pump. I had to replace myrear tank & pump recently.

 

I've already changed my fuel filter. Yeah I've heard that 4.9s should be at 50-60psi. I just wanted to make sure. Now, it sits at 45psi at idle what about when it's running.. Like actually going on the road. Should it stay at 50-60psi or drop?

 

I just found this at this websitehttp://troubleshootmyvehicle.com/ford/4.9L-5.0L-5.8L/how-to-test-the-fuel-pump-2:

"With the key on, engine off (KOEO), the factory manual says fuel pump pressure should be between 30 to 45 PSI for the 5.0L and 5.8L V-8 engines. The KOEO fuel pressure for the 4.9L 6 cylinder is 45 to 60 PSI."

My rear pump had zero pressure no matter what, so I'm not sure what it should be when driving down the road.

 

You don't want pressure to drop under load. In fact, it should go up as you accelerate because intake vacuum is reduced during acceleration, and the pressure regulator applies more pressure to the fuel without as much vacuum to it. Makes sense bc your engine obviously consumes more fuel under load.

Your issue sounds like a weak pump that is slowly dying. A friend's truck did the same. Low on fuel, warm day, truck fell on its face under load. Add fuel (cools the fuel pump) and it was markedly better, same with driving at night (cooler pump). It was easier to diagnose on that truck because it had an air fuel gauge, and it pegged lean (over 18:1 AFR) under load. To confirm, I drove with a fuel pressure gauge on it. I saw pressure go from 40 psi at startup (cold pump, in specification) to 18psi under load when it feel on its face. I put a new pump in, and she's driven thousands of miles without issue.

 

That sounds just like my truck. But it does it on both tanks. Could both pumps be just as bad? I've also heard that fuel pumps "either work or don't" but what you're saying about your friends truck is what mine does. Hot summer days it runs like complete crap! As of now it's cooled down so at night's it'll run okay till it warms up after 15-20mins of driving... And Uphills! Forget it! I'm lucky if I make it up without starting to over heat.. I love this truck but..

 

xUPDATEx

So I rechecked my fuel pressure and mess with the Fuel Pressure Regulator this time, since I didnt last time. I unhooked the vacuum hose from the FPR and from 45psi it went up to 52-53psi. Turned off the truck and pressure still at 52psi. So this means my FPR is working good, right? I shouldn't replace it? Also switched tanks while running and psi stayed the same, 45psi with vacuum on. And 52-53psi with vacuum off.

 

UPDATE * PROBLEM FIXED *It ended up being the Timing. It was at 4° when it should be at 10° but we ended up bumping it to 12° cause I guess thats the sweet spot on these trucks. I have the 1996 4.9 Inline 6. Not sure if it's the same degree on the 5.0 or 5.8 but it is super easy to do. Check out some YouTube vids. I also changed out the Oxygen Sensors, my truck had 3. My truck had no power on the highway at higher speeds, it would overheat pretty bad, needle guage would sit between M-A (on NORMAL) once it would get that hot, there was no power, I'll floor it and nothing. Almost like it would go on Limp Mode. It would want to stall. If I had the AC on it would get even worse. Fixing the Timing fixed the power, speed issue and it doesn't get hot anymore. With the AC on it runs just as good. Hopefully this helps someone.