I bought a 78 F 350 and disconnected rear fuel tank and ran a straight line to the new fuel pump that I installed, for some reason, there not enough engine pressure to get fuel from gas tank to the line going into the carburetor, could someone assist me with the problem?
Thank you

 

Hi Hunter
Welcome to FTE
First off, tell us about the truck (ex. what engine) and why you disconnected the tank in the first place.
No way we can help without some details.

 

,
Its a 1978 F 350 with 400 engine, I disconnected the rear fuel tank because the sending units that were installed where bad and the owner had cut the wires, the fuel gauge isn't working, there no switch to hop from front tank to back tank...therefore I decided to just run a line from the front tank straight to the mechanical fuel pump. When I posted back 3 month ago, alot of replies said I could run a straight line in instead, so tthat's what I did and now I'm not getting enough pressure from fuel pump when I crank the engine over

 

Ok, if I understand you correctly, you have a dual tank truck in which the switching system does not work. The sending unit for the fuel gauge in the rear tank does not work either.
So you have gone around all your problems and connected the rear tank directly to your mechanical fuel pump.
You say that "now" it is not working. Did it work at one time?

 

No, when I bought it, the guy told me his father in law had problems with the fuel pump, hence the box of fuel pumps that came along with the truck..lol. He thought also that it was the sending unit that wasn't working either, therefore the reasoning of by passing the problem.

 

Ok
More new info
I'm thinking that you should start at the root of the problems.
Pull the fuel tank and check to see how much crud is in it.
If it's going through pumps it could be sucking up crap from the tank.
These things get pretty damn dirty over time. Even the screens decompose and float around only to be sucked up.
Even if it's clean (which it won't be) you still need to verify your fuel system is clean start to finish.
Start at the tank and work your way to the carb.
The fuel lines from the back to the front can also become caked with rosin and garbage. They at the very least need to be blown out.
It's a time consuming job but needs to be done.
Have fun.

 

Hunter, If you just put on a new fuel pump and installed a new line to the tank, you can only have 3 problems. 1. fuel pump installed incorrectly, 2. gas tank very dirty plugging fuel line, 3. air getting in around hoses connecting at fuel lines. First thing unplug the coil wire at coil, get a empty milk carton put some gas into it then connect a hose from the inlet side of pump to carton, disconnect fuel line at carb. and put another container on the end of that line. Have someone turn engine over with key and see if gas is coming out of fuel line to carb., if not bad fuel pump, installed wrong or sucking air. Check these 2 things first. If still no fuel no alternative but to pull the tank. all mechanical fuel pumps do 2 things. 1. suck fuel from tank 2. push it to the carb. good luck bill Also just read about the box of fuel pumps that came with truck. make sure it's the right pump. It could also be the fuel pump eccentric is loose or broken. if that's the case the front of engine will have to come apart. nothing else put an electrical pump on.

 

How are you quantifying this observation? Are you actually measuring the fuel pressure delivered by the pump, and comparing it against a specification in the shop manual?

Or are you not even measuring fuel pressure at all? If you're not, then you actually have no idea what the fuel pressure is, or where it stands relative to something else. In that case, what is the actual problem? What do you expect the truck to do, and how does its current state differ from your expectations?

 

I'm not measuring with a gauge, I'm not a mechanic or have the capability of getting my hands and one..second I expect the truck to run after being fixed...

 

Will it not supply fuel at all? Or is it starving at higher speeds/acceleration?

Try the fuel into the container method to see how much fuel is actually being pumped in.

 

I'm not measuring with a gauge, I'm not a mechanic or have the capability of getting my hands and one..second I expect the truck to run after being fixed...everything was observation and feeling the pressure from the outflow line during cranking the engine

 

Wont pump fuel at all...I will try using a container again since I install the new pump this weekend

 

1. If you disconnect the fuel lines from the tank does fuel drain out?
2. Is the mechanical fuel pump the correct one and is it seated correctly?
3. Is the fuel filter new? Not clogged?
4. Disconnect the fuel line at the carb. Disconnect the coil wire(to keep the truck from starting). Collect the fuel in a container. Have someone help you by turning it over. About every two revolutions you should get a good squirt of fuel.

If it's not pumping at all and not cranking then you can't really test fuel pressure or actual volume.

No fuel pumping at all sounds to me like the following.
1. Clogged fuel inlet at/in the tank.
2. Fuel filter completely clogged.
3. Damaged line (metal line bent closing it off in line)
4. Corroded line and possibly internally blocked.
5. If fuel is getting to the fuel pump then maybe the fuel pump is not seated correctly. Make sure the fuel pump rocker arm is positioned correctly on the camshaft eccentric. You can turn the motor over to help in getting this at the low spot on the camshaft.
6. Did the front tank work? Maybe the switching valve is shot and not allowing the fuel to be pulled from the other tank.

If you try to clean out the lines just some advice do not use compressed air to blow them out. It can make for a bad day and possible fire or explosion. I have seen folks use compressed air to blow out fuel lines.

Look into these things and maybe that will help.

 

I would agree with billgrant's #1 problem indication - incorrect install - especially since it appears that you haven't had the "hands on training" you would like.

The fuel pump doesn't go in easily - takes a bit of beef to get the pump arm under the cam eccentric. If it went in as easily as closing a door, it's not right.

 

The engine should be at TDC any time a fuel pump is installed or removed. This places the eccentric at its lowest point, relieving all pressure on the fuel pump arm. The fuel pump will slide right in and out with no difficulty at all if the procedure is performed in this manner.

Otherwise, then yes, it can be extremely difficult to get a new pump to go in.