Alright folks, this is my first post on any of these forums; i'm looking for a little diagnostic help on my truck. I've got a 1996 F150 4x4 regular cab short bed with the 4.9L (300) and 3.55 gears and a 5-speed. I've got 31" tires on it. I bought it about 2.5 years ago and i've enjoyed it. i read that the 4.9 was a great engine-super durable and plenty strong. The whole time i've had it, it's been pretty gutless. I am no mechanic, but i am trying to learn as i go (that's what i bought the truck for, a project and learning to work on stuff). It accelerates alright, it doesnt feel like it would if the oxygen sensors were disconnected (done that), but it's still pretty weak, especially at higher speeds. I've towed a medium size trailer with it with a couple thousand pounds when i was moving one time and it took revving up really high to move it at all. Even with nothing in it except me, i've got to rev it up really good if i want to get it off the line with any speed at all. Since i've read that it's so strong, i'm thinking there must be something wrong with it, but not something that's a huge problem since it runs really smooth and never misfires. It runs best when i first fire it up in the morning and pulls pretty good for about a minute before it starts getting more sluggish. It is very slow to accelerate at highway speeds (again, with nothing in it except me). the only times it ever runs rough is sometimes when it's really hot outside it'll run really slow at idle and sound like it's gonna die (goes down to 500-600 rpm). I bought a bluedriver diagnostics tool that i've been trying to diagnose my issues with.

oh yeah, and when i first bought it, it didnt have any of the AIR stuff, which i had to get put back on so i could pass emissions in TX. only a couple more years before i dont have to worry about that stuff...

so i'm trying to diagnose what could be the reason that this thing is not very strong. It's got to be an issue that is less problematic right when it starts up, so that takes fuel pressure/injector issues away, which would be a problem all the time. also, my fuel trim readings show that at idle i've got a very high LTFT-2 (greater than 20%) which goes down when i open the throttle, which tells me i have a vacuum leak. And the trim has been steadily rising. I recently found a vacuum leak at my EGR valve and replaced the gasket. that knocked the LTFT down to about 12% at idle and its been rising back up over the last few weeks until my CEL came on again... my LTFT-1 shows normal readings, and drops to about -10% to -15% when i open the throttle. So i've got a rich condition at bank one at open throttle, and i've got a lean condition at bank 2 when idling. doesnt make sense. my bluedriver thing shows that the oxygen sensors are going back and forth between 1 volt like they should...

any help would be greatly appreciated. i can upload a plot of the scan data or a table with the data if that would be helpful. thanks guys.

PS, i thought about maybe checking the timing, but i can't see the timing marks. Seriously i dont know how anybody gets down in there and sees it, i've seen other pictures of these things and it looks like my truck has more sensors and other garbage in the line of sight between where you're supposed to look/shine the light and the harmonic balancer. i'll snap a picture sometime soon... They say these old trucks have plenty of room to work, but man some of these things are so hard to get to. I am also needing to check and probably replace my engine coolant sending unit and can't even see it. i know where it's supposed to be, but can't see it for the life of me. tried to do a fuel pressure test and that shrader valve is so hard to get to. took me 5 minutes to get the plastic cap off. and somehow, the threads don't match the tool i bought. same diameter, just different threads, so fuel was dripping all over the place...I want to check/replace the fuel pressure regulator as well, but it's under the intake manifold and looks impossible to get to.... man.

 

 

only code i've got right now is P0174 which is bank 2 system lean, which is triggered when LTFT is over 20%. at idle it's sitting about 22% right now.

 

I'm guessing that 96 was OBD 2? If you cannot track down a vacuum leak and the OBD2 trucks are running MAF, unplug the MAF sensor to let the fuel tables go to default values and see what the fuel trims do.

If its a MAP system, check out this video:

 

It is. To the OP: I have an identical truck to yours. Maybe I can offer a real-world opinion. When I got my truck I had never driven an I-6 Ford. I read forums that all said "oh yea 300's got great power" n all kinds of stuff. So I decided to fix it up. I've got the same code: both bank 1 and 2 lean (I think due to bad O2 sensors and leaking upper AIR) My thoughts:

The 300 is no powerhouse. Yeah it's got adequate power but my truck is slow. I can do 70 on the interstate but she really prefers 60-65. I can pick up to 75 to pass people but I don't find myself doing that much. Stop and go traffic is where I have issues, but then I remember - I'm trying to keep pace with brand new technology that puts out a lot more than the 145 HP I'm pushing. So I keep to the right lane and when they honk at me I give em a smile and the finger.

Realistically, you might have a legitimate problem, just don't expect too much out of the BBS - it is like 40 year old technology. I really wanted to swap a V8 into my truck, only thing stopping me is laziness and a (maybe misplaced) sense of pride that I'm driving a truck with the last great inline six truck motor in it.