My 86 f150 xl longbed hasnt been used for about 2 years and we recently decided to fix it up. When i started driving i realized when i pushed the gas it would buck and jump violently. the fastest i can get it up to is about 30 mph without it bucking. We changed the spark plugs and wires put new filters and all new fluids, and recently drained the gas because it was 2 years old. Now weve developed a new problem. We put new gas in it and couldnt start it after trying for about 30 minutes with starter fluid we decided the fuel pump was gone so we bought a new one and installed it and the fuel line running from the gas tank to the fuel pump wasnt putting any gas out when it was unhooked from the fuel pump and my dad took a air hose and ran air through it to see if it was clogged but it wasnt and no fuel would come out..Any ideas?

 

If it won't run on ether than it's a spark problem. It's 3 times for flammable than gasoline. Take the line off where it hooks to the carb and crank it over. If you're getting fuel u'll know it!!

Evan

 

If your truck has EFI then it has two fuel pumps. A low pressure pump in the tank and a high pressure pump on the frame. If you only replaced one of these, then you may want to check to see if the other one is working. If you are not getting fuel out of the tank, the pump in the tank isn't working. It could be the pump or something electrical going to the pump(s). Remember most electric pumps are used to "push" the fuel, not "pull". Just something to think about.

Kyfordman

 

Jason, I read your post again and figured you have carb. since you were using starting fluid to try to get it started. I looked in my Haynes manual and it gave some ideas. The same symptoms of a faulty fuel pump could also be a clogged carburetor float bowl filter, a clogged intake filter in the gas tank, kinked lines, or faulty electrical system. The manual also says that some of 7.5L trucks had a "Hot Fuel" option where the fuel system used a carb. as well as a low pressure pump in the tank. I don't deal with carbs. that often but I just figured I would give you some ideas. If you specify wether your truck is carbed or fuel injected I'm sure you will get some help here.

Kyfordman

 

its fuel injected

 

Your in-tank pump is definatley not working. I'd almost bet that it's dead... My F250 has the hot-fuel setup(carb with in tank pumps,) it had only sat for 3 months before I got it and both pumps were dead.
Evan
86 F250 HD XLT Lariat Explorer 4x4 ex. Extended Cab: 460/T19(syncroed granny low)/BW 1345/3.55 geared Full Floater 10.25 and Dana 50 TTB/ 265/75R16 Hankook FR04's on 16x8 Whitespokes(street tires... Need mudders)
78 F150, 351M/C6, eventually to be repowered with a 400

 

Any ideas what might be causeing my truck to buck and only go 35 mph??

 

Jason, un-reliable fuel pressure will cause it to buck. at 30 mph your probably needing more power due to wind drag and rpm, and thus more fuel. you can have aclogged fuel filter or one of the pumps may be bad, or even, your fuel return line may be clogged, though i highly doubt it, it's get a fuel pressure guage and hook it to the schrader valve.

instructions for "cheap *** fuel pressure guage"

go to home depot and get a air pressure guage from the air compressor section (try to get the lower one if you can (100 psi) but it don't matter which really) now go to the auto shop and get about 5-10 feet of FUEL INJECTION HOSE (rememebr we're no longer talking 6 psi with fuel injection) use hose clamps and connect one end of the hose to the guage and duct tape it to your windshield and use then take the valve out of hte schrader valve and then clamp the other end of the hose to the "valve" now go for a ride and see what the fuel pressure does when it bucks. I know that it'll be difficult to get hte hood to close without pinching the line (the cars i do this to dont' have the trucks hood line) perhaps you may need longer hose so you could rout it some way other than out the cowl, but this is how i test fuel pressure on my turbo cars.